Category: Anthropology and Geoarchaeology

A biface, Acheulean hand axe is more than object of beauty produced by exquisite skill, this industrial genre was invented by African Homo ergaster around 1.6 Ma ago, became a central feature of Palaeolithic archaeology, and lasted until the last few hundred thousand years. Nobody doubts that production of these objects implies a brain that fashioned able to visualise a complex shape within a shapeless lump of rock and to devise a way of achieving it. Moreover, its longevity spanning several species of Homo to our own shows that skills were efficiently passed down through hundreds of thousand generations: possible evidence for linguistic skills in the makers and teachers. But what was it for? Experts have been at a loss to agree on a function: too heavy for hafting to a spear; more awkward for cutting than earlier Oldowan pebble fragments; produced with careful three-dimensional symmetry when a hand tool needs none; time consuming to make yet often found in great abundance and apparently hardly used. One idea is that they were in fact for throwing, in the manner of a discus, yet broken biface axes are rare. A more appealing hypothesis is that they were made for ‘show’ as an element in human sexual selection (Kohn, M. & Mithen, S. 1999. Hand axes: products of sexual selection? Antiquity, v. 73, p. 518-526). Kohn and Mithen argued that the primary function of hand axes was to advertise a maker’s “good genes”: an indicator of the knap­per’s geographic knowledge of suitable resources; his ability to execute a plan; his dexterity and patience; and his so­cial awareness. Those are all attractive qualities in a potential mate. They also suggested that the axes’ often near-pristine quality and occurrence in great numbers at some sites indicate that once their purpose was served, they were thrown away: ‘That man is so cool, he must be good at surviving’. Ten years after Kohn and Mithen first mooted the hypothesis it has come under criticism by April Nowell and Melanie Lee Chang, of the universities of Victoria, Canada and Oregon USA, respectively  (Nowell, A. & Chang M.L. 2009.The case against sexual selection as an explanation of handaxe morphology. Paleoanthropology, v. 2009, p. 77-88).

The critique begins by examining Kohn and Mithen’s interest in symmetry as an element in attractiveness, that Nowell and Chang concede, but consider to have arisen not in a sexual context but in development of vision, despite vision being an evolutionary ‘given’ vastly older than hominins. After a discussion of how fully modern human females base their sexual choices on non-physical attributes of potential mates, such as “niceness,” intelligence, sense of humour, compatibility, willingness to work hard and evidence that the partner in question is attracted to them, Nowell and Chang examine available archaeological evidence. Much of this concerns the ‘absence of evidence’. For instance, there is no evidence to suggest that females did not make hand axes and living females in gatherer-hunter societies do make tools. Other criticisms include: the absence of hand axes from Asia until migration there by H. sapiens [but the biface axe had not been invented when H. ergaster migrated there from Africa around 1.8 Ma]; not all biface axes are symmetrical [but they are nonetheless impressive]; and axes in large numbers generally occur where prey has been butchered, as at Boxgrove, and may have accumulated by hundreds of years of use and loss at such sites by seasonal hunting. The most serious criticism is that some hand axes do show minute patterns that indicate that they were used; although most axes have never been examined for wear patterns. My own conclusion is that the critique is based on absence of evidence for biface axes as ritual objects in sexual selection, but that is not evidence of absence, and I wonder if the 10 years taken to bring together contrary evidence has a bit to do with casting doubt on a not quite ‘PC’ idea. There are many intriguing facets of the fossil and archaeological records of hominins, none more so than those which may have a cultural connotation, like ochre caches (see Deeper roots of culture in EPN of March 2009) and the tear-shaped Acheulean axe. For most we may never know their true context, but can be sure that any curiosity and imagination we apply are reflections of imaginative and curious forebears.

Homo erectus in a cold climate

The famous Zhoukoudian Cave where Peking Man, now known to have been Homo erectus, was first found in 1929 is a lugubrious place. It seems the hominin fossil remains of at least 40 individuals were dragged there and eaten, hopefully by predators. They are by no means the oldest Asian hominins at less than 1 Ma, and their ancestors, probably African H. ergaster, migrated that far around 1.6 to 1.8 Ma ago. Until this year, decent ages from Zhoukoudian were a problem: the errors on estimates of around 500 ka were too large (the likely time lies in a ‘datability gap’ between the capabilities of Ar-Ar and ¹⁴C dating methods) to see if the hominins were living at such a high latitude (40ºN) in warm or cold conditions. The latter would be of great interest as it suggests both the use of fire and clothing, and probably adaptation to cooked tubers. In fact, even in the current interglacial episode Beijing gets mighty cold in winter. However, cosmic-ray bombardment can produce unstable isotopes that are suited to dating in that gap, provided materials have been exposed to them. The fossil-containing sediments in Zhoukoudian Cave contain quartz that was exposed at the surface and washed in at the same time as H. erectus individuals were dragged in. Decay of cosmogenic ²⁶Al to ¹⁰Be and measurement of parent and daughter isotopes in quartz grains have yielded ages of 770±80 ka, somewhat older than earlier estimates (Shen, G. et al. 2009. Age of Zhoukoudian Homo erectus determined with ²⁶Al/¹⁰Be dating. Nature, v. 458, p. 198-200). This age roughly correlates with layers in the western Chinese windblown loess deposits that were deposited during the dry conditions of a minor glacial episode.

See also: Ciochon, R.L. & Bettis, E.A. 2009. Asian Homo erectus converges in time. Nature, v. 458, p.153-154. Gibbo0ns, A. 2009. Ice age no barrier to ‘Peking Man’. Science, v.  323, p. 1419.

 

Walking with the ancestors

From time to time the most evocative hominin trace fossils come to light, such as the Australopithecus afarensis footprints fount by Mary Leakey at Laetoli in Tanzania. A recent one is of footprints of a probable H. ergaster dating back to 1.5 Ma near Lake Turkana in Kenya, not far from the site of the famous ‘Turkana Boy’ skeleton of the same species (Bennett, M.R. and 11 others 2009. Early hominin foot morphology based on 1.5-million-year old footprints from Ileret, Kenya. Science, v. 323, p. 1197-1201). Not only does the trackway reveal details of flesh, skin and bones of the feet, but careful analysis of 3-D scans of the prints, in the context of the mechanical properties of the material walked upon, allows the authors to show that the person who left them moved in essentially the same way as do we when walking through soft mud. They are distinctly different from the Laetoli prints, showing arches and very distinct big toes that are so necessary for ‘springiness’ and bipedal balance respectively.

See also: Crompton, R.W. & Pataky, T.C. 2009. Stepping out. Science, v. 323, p. 1174-1175.

There has long been a pervasive aroma of eurocentrism in cultural palaeoanthropology, encouraged by the spectacular cave paintings in southern France and northern Spain that are no more than 40 ka in age and the first to be discovered. This undoubted flowering of art as we appreciate it today has been linked to much more than figurative expression. Some have argued that Homo sapiens only became fully human after Europe was colonised. Thankfully, the archaeological record is rapidly being set straight by more and more discoveries of symbolic representation from elsewhere (Balter, M. 2009. On the origin of art and symbolism. Science, v. 323, p. 709-711). Blomberg Cave In South Africa is a repository for 100 ka old inscribed ochre artefacts (Balter, M. 2009. Early start for human art? Ochre may revise timeline. Science, v. 323, p. 569), which represent symbolism of some kind and the imagined uses to which the ochre was put – ritual or cosmetic body painting? But there are tantalising objects that push art back even further. In 1999 a cache of stone tools at Tan-Tan in Morocco was found to include a 6 cm quartzite chunk that looks like a rough version of the ‘Aurignacian Venuses’ of later times, yet the find dates back to 300 to 500 ka. Something similar turned up in the 250 ka site of Berekhat Ram in the Israeli-occupied Golan Heights of Syria. Both predate the evolution of fully modern humans. And what of the tear-drop shaped biface ‘axes’ associated with H. erectus and H. ergaster as far back as 1.6 Ma? These are extremely odd objects, for several reasons: it is hard to visualise their use; many finds are in pristine condition, as if never used; to make one demands a mental model of what potentially lies within a rock; they are more difficult to make than later blade tools that are more utilitarian. Arguably, the ‘Acheulean hand axe’ may be more of a symbol than a tool.

The reason for renewed discussion in print of these matters is, of course, the bicentenary of Charles Darwin’s birth and the 150th anniversary of publication of his Origin of Species. Darwin drew a link between tool making and language in his Descent of Man. He would have been delightedly surprised to learn details of the emergence of new tool-making skills in Africa, from where he insisted we all came (Morgan, L.E. & Renne, P.R. 2009. Diachronous dawn of Africa’s Middle Stone Age: New 40Ar/39Ar ages from the Ethiopian Rift. Geology, v. 36, p. 967-970). Morgan and Renne, of the University of California at Berkeley, discovered that the oldest sites in the Main Ethiopian Rift that contain the novel tools that mark the onset of the Middle Stone Age (MSA) span a much greater interval than assumed hitherto. In one site such tools date to 276 ka, whereas at another such objects appear only at 183 ka. The more delicate work to make MSA points and blades, and a much diversified ‘tool kit’ has been called the Levallois technique, thought to have been associated with a cognitive leap from the Lower Palaeolithic Oldowan and Acheulean techniques. For some it came to signify more: the appearance of fully modern humans. But the new ages do not tally with the fossil record of H. sapiens or with estimates from mitochondrial DNA molecular clocks. All in all, culture, whether art or technology, seems to be characteristic of the genus Homo. Given a push bike, could H. ergaster have ridden it and, more important, had fun? What would a Neanderthal, male or female, have done with a tube of lipstick?

The Neanderthal genome is coming!
Some computer owners take part in the search for extraterrestrial intelligence, allowing SETI to combine their processing power with that of hundreds of others, on the off chance that the meaning of  (pi) pops up in a systematic burst of non-static microwaves. Personally I would far rather wait for a message from a relative than from some seriously weird being whose motives we might never guess. A Neanderthal lady – more precisely her leg bone –from Croatia is very close to speaking volumes about our own history. Two teams of DNA sequencers are putting the finishing touches to her genome. That it would ever happen was a fevered dream not so long ago. That it will opens up a revolution in understanding our origins. To keep in touch, read Elizabeth Pennisi’s account of the pending revelations (Pennisi, E. 2009. Tales of a prehistoric human genome. Science, v. 323, p. 866-871). Svante Paabo gave a glimpse of his team’s rough draft of the genome at the AAAS annual meeting in February 2009. When analyses are finished palaeoanthropology will explode onto the news channels, blogs, and among the twittering classes. Should SETI get a result, I would first eat my trousers and then prepare to be eaten myself. As for Darwin, maybe you have noticed his prominent brow ridges…

The period between 300 and 30 ka was critical for the evolution of modern humans. Our mitochondrial DNA indicates that fully modern humans emerged around 200 ka. Projectile weapons that help define the epoch first appeared. Clear signs of self-adornment and symbolism also turn up during the Middle Palaeolithic. All of these developments took place in Africa, and the last two are reflections of the increased efforts by archaeologists in the continent from which we all originated. There is a long way to go to match the density of sites from which later periods in human history have been outlined in Europe, but progress is accelerating. One great hindrance has been dating sites, for the Middle Palaeolithic lies in a time zone where the Ar-Ar and ¹⁴C methods are ineffective. A developing chronological ‘workhorse’ for this difficult period depends on the way in which exposure of sand grains to sunlight ‘heals’ the defects in their molecular structure formed when radioactive isotopes in soils emit ionising radiation. Artificial illumination of sand grains containing these defects causes them to luminesce. The degree of luminescence is related to the time over which the defects have built up. Optical dating relies on grains having been exposed at the surface for a time to ‘reset’ the luminescence clock, and then being buried so that new defects can accumulate. Having lots of sunlight and a superabundance of bare sand, Australia has become a hotbed of research into optical dating of events associated with its peopling during the last ice age. Expertise developed there has been applied to many Middle Palaeolithic sites in Southern Africa (Jacobs, Z. et al. 2008. Ages for the Middle Stone Age of Southern Africa: Implications for human behaviour and dispersal. Science, v. 322, p. 733-735).

Archaeological work in South Africa and Namibia has revealed two distinct stone industries in the Middle Palaeolithic, both of which made hafted weapons that would have made hunting more efficient than the whatever weapons were used in earlier times – the most distinctive of the preceding Lower Palaeolithic tools was the bifacial hand axe, whose use is obscure. Both cultures involved the earliest recognisable ornamentation, such as shell beads and materials engraved with symbols, together with indirect evidence for the use of hematite and goethite pigments for body painting (see When and where ‘culture’ began in EPN of November 2007). Genetic evidence famously places modern human origins and their global migration out of Africa within this time frame. So, dating the archaeological sites as accurately as possible is a crucial importance, and a tremendous start has been made by the multinational team lead by Zenobia Jacobs of the University of Woolangong in Australia. Optical ages span 90 to 30 ka, with clusters between 71.9 to 71 ka and 64.8 to 59.5 ka, with a statistically significant gap of about 6.7 thousand years between them. When compared with climatic-change indicators from the Antarctic ice record the developmental episodes do not seem to correlate clearly with any specific warm of cool periods, though the earlier spans the time of the Toba super-eruption in Indonesia and the later one was a period of warming. So any environmental cause for the technological and cultural changes is unclear. However, both fall within the estimated time span of the genetic ‘bottleneck’ between 80 and 60 ka, and the most likely times for the initial ‘Out of Africa’ migrations, probably across the Straits of Bab el Mandab linking Eritrea and Arabia across the Red Sea shallowed by ice-cap linked falls in global sea level.

Childhood and families

Human females are unlikely to break 10 seconds for the 100 metres because of their sashaying gait. It can’t be helped, being due to the evolution of the pelvic girdle of bipedal females to deal with birthing of infants with increasingly large heads. Supposedly, the human female pelvis is now close to the limit that will permit walking on two legs. Such problems do not plague other living primates partly because their young have small heads relative to their bulk, and pelvic anatomy is not constrained by an habitually upright gait. It seems not to have been an ‘issue’ for australopithecines either: they did not possess ‘child-bearing hips’. The intermediate species, Homo erectus, despite having a 1 Ma fossil record (maybe as long as 1.8 Ma for the Asian form) only recently provided substantial pelvic remains (Simpson, S.W. et al. 2008. A female Homo erectus pelvis from Gona, Ethiopia. Science, v. 322, p. 1088-11092). In the words of the authors, this pelvis is ‘obstetrically capacious’ and demonstrates that female skeletal evolution responded to increasing foetal brain size: it would have permitted infants with heads 30 to 50% of the adult size to have been born. Homo erectus has been widely supposed to have had a tall willowy frame analogous to that of fully modern human inhabitants of tropical savannahs, yet the Gona woman was stocky. So, environmental influences seem to have had less of an evolutionary role than the advantages of greater brain development before birth. That places H. erectus even more firmly on the human line; indeed greater in utero brain development seems to have taken place than in modern humans.

The Gona pelvis demands re-evaluation of how foetal and childhood development has progressed over the last two million years (Gibbons, A. 2008. The birth of childhood. Science, v. 322, p. 1040-1043), the unique attributes having appeared during the evolution of our own genus. Among chimpanzees, infants can fend for themselves, with a little help from elders, after 3 years old. Street children from Asia and South America need to be 6 before they can survive without parental care. Growth lines on teeth that appear week by week reveal that previous age estimates for a number of immature australopithecines whose first adult molars had erupted were large overestimates: instead of 6 they point to 4 years old. Another signal feature of human development is the lengthy period to full development (marked by the eruption of the 3^rd molar as well as the end of significant growth in stature). The average age when human child bearing begins is around 19, while chimpanzees start at about 11. A fresh examination of the famous Turkana Boy’s skeleton, an H. erectus, that uses tooth microstructure reduces his age at death from 13 to 8, suggesting an earlier onset of independence than in modern children. He grew much more quickly too, and would have reached adulthood somewhat earlier: around 14.5 years old. The picture with Neanderthals is not completely clear, some tooth studies suggest that their children grew significantly more quickly than modern ones, other studies point to the same rates or even longer development if adult brain sizes of Neanderthals are taken into account (larger on average than those of modern humans). Using average life expectancy of gatherer-hunter humans and chimps who survive dependent childhood – 45 and 70 years respectively – along with evidence for child development, suggests that australopithecines could have reached 45 while H. erectus adults could have expected to reach 60 years old.

There are other differences that begin to slot into space with the new data. Both human and chimpanzee females have a similar child-bearing period of around 20-25 years. The difference is that, on average, the natural interval between births is about half as long for human mothers as for chimpanzees. The greater number of human offspring gives a greater chance of the survival of some to reproduce themselves. On the other hand, slower child development places a greater burden on mothers, even after weaning. So there is quite a contradiction between the evolutionary effects, if only child-mother relationships are taken into account. This contradiction was resolved, to some extent, by a seminal paper in the late 20^th century by a group of anthropologists from the Universities of Utah and California (see O’Connell, J.F., Hawkes, K. & Blurton Jones, N.G. 1999. Grandmothering and the evolution of Homo erectus. Journal of Human Evolution, v. 36, p. 461-485). They focussed on the potentialities of the early onset of infertility or the menopause among women relative to its appearance among female chimpanzees, which gives, on average, a 30 year non-child-bearing period to older women. This approximately coincides not only with child-rearing periods for their daughters, but for their granddaughters as well. The ‘grandmothering’ hypothesis for human development centres on the great evolutionary advantages of post menopausal women assisting with child rearing. O’Connell et al. suggested that this arose among H. erectus, as far back as 1.8 Ma, and the Gona pelvis together with other new views of H. erectus development add considerable weight to that concept. As well as freeing younger women for food gathering, the cultural significance of older women caring for children adds another dimension that may link to the advantages of delayed post-weaning development that we see today, albeit in many annoying contexts!

Which human species first controlled and used fire has been debated for as long as archaeologists began to realise we had a long and complex ancestry. Because sites can easily be contaminated by charcoal from natural fires it has been difficult to present convincing evidence. But there is a way to get believable data. Stone tools and fragments from their manufacture may have fallen in fires set by hominins, and show changes caused by intense heating. One such example comes from a long-occupied site in Israel (Alperson-Afil, N. 2008. Continual fire-making by Hominins at Gesher Benot Ya‘aqov, Israel. Quaternary Science Reviews, v. 27, p. 1733–1739). Nira Alperson-Afil of the Hebrew University of Jerusalem investigated small flint artefacts, probably flaked off during tool making, from eight levels excavated at the site. In all of them some flint shards showed signs of extreme heating, such as discoloration, crazing and tiny bowl-shaped pits (‘potlids’) resulting from exfoliation of hot flint surfaces. The features are reproduced by experimental heating of flint shards, and do not occur in those that have not been heated above 300ºC.

Gesher Benot Ya‘aqov was first occupied around 790 ka, by Homo antecessor, and the excavation levels may span around 100 ka. The site is the earliest to provide convincing evidence not only for the use of fire, but that it was a continuous part of the hominins’ culture: they could make it at will. Alperson-Afil suggests that fire making may have been an integral part of the Acheulean culture, well known for finely crafted biface axes, since its inception around 1.6 Ma ago. Ambiguous evidence for hominin fire use, such as burnt bones and reddened sediments, has been found at several sites in Africa dated between 1 and 1.5 Ma. Alperson-Afil’s meticulous micro-forensics should help African archaeologists and those working at very old sites left by migrating hominins in Georgia and Asia to check whether fire has such a long-lived place in our evolutionary history.

 

Because sea levels rose world-wide after the last glacial maximum, archaeologists have been largely stymied as regards exactly where migrating people lived and what they did. Much migration since fully modern humans left Africa around 70-80 ka is likely to have been ‘strandloping’ along coastal lowlands exposed as sea level fell as the last glacial period developed. Of course, this vast area is now drowned. It takes both a lot of work and a degree of good fortune to make anything of this landscape for ancient humans. Luck definitely played its part in getting some clue about one of the last of the migrations: from continental Europe to the British Isles, in the aftermath of the last glacial maximum. Trawlers have dredged not only animal bones from what was a great plain where the North Sea now sits, but also a superb bone harpoon point recovered in 1931. It has been a while in coming, but researchers at Birmingham University, UK have finally defined and mapped that drowned land area – Doggerland (see: Spinney, L. 2008. The lost world. Nature, v. 454, p. 151-153).

The hominin genus Paranthropus rarely hits the front page by comparison with the related australopithecines, despite their having had jaw and cheek bones that would put Sandy Shaw and a variety of 60s catwalkers to shame. (It is only polite to observe that there the vague similarity ends, for paranthropoids have a bizarre skull crest for attachment of jaw muscles and brow ridges that were probably better than a baseball cap at preventing glare.) The first (P. boisei) to be unearthed at Olduvai, Tanzania in 1959, was dubbed ‘Nutcracker Man’ by its finder Philip Tobias. Despite having formidable chewing tackle to drive its massive flat, thickly enameled cheek teeth, wear on their surfaces is little different from that on the teeth of ‘gracile’ australopithecines. (Ungar, P.S. et al. 2008. Dental Microwear and Diet of the Plio-Pleistocene Hominin Paranthropus boisei. PLoS ONE, v. 3, on-line e2044 (www.plosone.org) doi:10.1371/journal.pone.0002044). They show no sign of the microscopic pitting that characterises teeth of living primates that eat hard, brittle foods, such as nuts or woody stems.  Similar studies of the teeth of P. robustus show insufficient wear to suggest an habitual diet of that kind, although it may have eaten such foods when others were in short supply. Chances are that huge jaws and big teeth evolved to give paranthropoids a wider choice of diet and hence greater fitness in a climatically fluctuating terrain. It seems they chose to eat soft foods when available, as do gorillas today. In any event, they were remarkably successful creatures, and the two species cohabited the East African savannah with several human species, including H. erectus, for around a million years from 2.2 Ma when they appeared. Carbon-isotope data obtained from 20 paranthropoid and 25 australopithecine teeth by other researchers reveal a broad but similar diet for both, i.e. a mix of grasses and fruits, suggesting both had eating habits that could shift from apes to those of baboons. However, such C-isotope data cannot distinguish between exclusive vegetarianism and eating the flesh of herbivores. Low dental wear is also associated with meat eating…

See also: Gibbons, A. 2008. Australopithecus not much of a nutcracker. Science, v.  320, p. 608-609; part of a report on the April 2008 meeting of the American Association of Physical Anthropologists

For decades palaeoanthropology of the Americas has been dominated by a single idea; that nobody entered the continents before those people who used the elegant fluted spear blades first found near Clovis, New Mexico in the 1930s. These were eventually dated at a maximum age of around 13 ka before the present. One reason for accepting the Clovis people as the first Americans, apart from the lack of conclusive evidence for any earlier occupation, was the fact that glaciers blocked the route from the Bering land bridge of the last Ice age until about 13 ka. Increasing evidence has suggested earlier penetration by people who did not use Clovis tools from Asia, which reached Chile by around the same time and possibly as early as 33 ka. However, none of the evidence is definitive and the Clovis First hypothesis has been stoutly defended against this growing body of contrary evidence.

The ‘traditional’ idea of American occupation by humans after 13ka has taken a double whammy from an unusual set of fossils – of human excrement – discovered in a cave in Oregon. These have been dated at up to 15 ka and are unmistakably human, containing human mtDNA with genetic signatures typical of Native Americans (Waters, M.R. & Stafford, T.W., Jr. 2007. Redefining the Age of Clovis: Implications for the Peopling of the Americas. Science v. 315, p. 1122-1126; Gilbert, M.T.P et al. 2008. DNA from pre-Clovis human coprolites in Oregon, North America. Science, DOI:10.1126/science.1154116).

Ideas of how and when the Americas were colonised are changing rapidly after decades of ossification. A fascinating article in the 14 March 2008 issue of Science magazine reviews the issues and prospects (Goebel, E. et al. 2008. The late Pleistocene dispersal of modern humans in the Americas. Science, v. 319, p. 1497-1502). Genetic studies of living native Americans suggest their common ancestry in a Siberian population no earlier than 30 ka, and perhaps as late as 22 ka. The Beringia land bridge had repeatedly created a possible migration route during every major glaciation followed by many of the Pleistocene mammals that inhabited the Americas, but not by humans until the late stages of the last glaciation. Dating of archaeological sites and remains, including the human coprolites found by Waters and Stafford, is slowly pushing back the earliest evidence for a human presence to around 15 ka, several trhosand years before the Clovis culture appeared. Sometime before that, the first Americans had arrived and begun to spread. Ice barred their way through the interior of Alaska and NW Canada, and they must therefore have travelled along the coast, where the way was open from Beringia to Cape Horn; perhaps they used boats to move along the flat, but frigid shores of Beringia and the rugged western seaboard of North America. Early populations subsisting on shoreline resources would not have needed the heavy projectiles of the Clovis culture that are more attuned to ‘big-game’ hunting on plains. That may explain the sudden appearance of Clovis artefacts once access to plains was possible around 13.5 ka and its equally sudden disappearance at the start of the Younger Dryas around 12.8 ka when survival on icy plains would have become very difficult. Interestingly, the period of occupation of Siberia around 30 ka, would have presented the Beringia route to migration to North America when climate was similar to that following the last glacial maximum. So far, no tangible evidence

Homo floresiensis had big feet

Controversy has raged about her identity since the skull of a minute female hominin was unearthed from the Liang Bua cave on the Indonesian island of Flores. On the one hand are authorities who believe the fossil is that of a distinct human species, while on the other are sceptics convinced that the diminutive stature and chimp-like brain capacity reflect some pathological issue in a population of ordinary humans. The 12 April meeting of the American Association of Physical Anthropology in Columbus, Ohio (see Culotta, E. 2008. When hobbits (slowly) walked the Earth. Science, v. 320, p. 433-435) were treated to an anatomical exposition of the rest of the Liang Bua skeleton. A great deal more turns out to be different from human characteristics, including the legs and feet. Amusingly, for J.R.R. Tolkien’s Hobbit had them, the feet of H. floresiensis were disproportionately large. Also, her gait was quite different from ours – a kind of careful, high-stepping plod. Although not all agree, the post-cranial bones of H. floresiensis appear to bear close resemblance to those of early Homo species. Those favouring a separate species from our own suggest either that it arose through allopatric speciation from SE Asian H. erectus  after isolation of a population on Flores, or perhaps even that it is a relic of an early migration of H. habilis from Africa almost 2 Ma ago. Whatever, it is now going to be even more difficult not to speak of hobbits.

Orrorin walked the walk

Orrorin tugenensis is one of those fossils over which palaeontologists tend get heated. It is a hominin, old (~6 Ma) and fragmentary, so it just might be the daddy of us all. That possibility takes a significant step forward with statistical evidence that Orrorin walked upright in a similar manner to the much later australopithecines and paranthropoids (Richmond, B.G. & Junggers, W.L. 2008. Orrorin tugenensis femoral morphology and the evolution of hominin bipedalism. Science, v, 319, p. 1662-1665). The study was made independently of the original discoverers, who claim that the femur has especially human-like features. Whichever, one of the original suggestions that Orrorin  was on the ancestral line to gorillas has become improbable. The creature clearly displays the oldest known example of a bipedal gait (the older Sahelanthropus (~7 Ma) is known only from skull fragments and teeth, although its skull’s foramen magnum hints at bipedalism). In itself, Orrorin’s walking biomechanics is remarkable, as molecular evidence suggests that the branching that led to chimpanzees and to hominins is not much older than 6 Ma. It does seem as if that phylogenetic split may well have centred first on adaptation for traversing open ground from a forest common ancestor.

Colonisation of Europe pushed further back

Europe is so close to Africa that in recent years repeated waves of immigrants have crossed the Straits of Gibraltar, often on frighteningly flimsy craft. Their driving force is simply the search for a better life in the booming economies of Spain and Italy. Far more intense pressure from deteriorating climate and vanishing game drove Africans of many earlier times to escape their home continent, reaching back almost 2 million years. So how come the European hominin record is so short? At last count it went to H. antecessor around 750 ka, albeit a species that was sufficiently adventurous to reach British shores (see Earliest tourism in Northern Europe in EPN of January 2006). The famous Sierra de Atapuerca cave systems in northern Spain have now yielded clear evidence of much earlier occupants from around 1.1 to 1.2 Ma ago in the form of a lower jaw fragment in association with tools and bones showing signs of butchery (Carbonell, E. and 29 others 2008. The first hominin of Europe. Nature, v. 452, p. 465-469). Provisionally, the person has been assigned to H. antecessor, and there are two possible interpretations: either (s)he was a new immigrant from Africa, or represents a new speciation in northern Spain from an earlier population of African colonists. The paper’s title may prove to be premature.

 

Sébastien Chabal, the gigantic and hairy back-row forward in the 2007 French World Cup rugby team, was nicknamed ‘The Caveman’ by French fans. Indeed he is an awesome spectacle, at almost 2 m tall and weighing over a tenth of a tonne, with great black beard and locks. But is seems that Neanderthals were redheads and probably prone to sunburn (Lalueza-Fox, C. and 16 others. 2007. A melanocortin 1 receptor allele suggests varying pigmentation among Neanderthals. Science, v.  318, p, 1453-1455). The team analysed DNA extracted from Neanderthal bones from Spain and Italy, and identified the mc1r gene that regulates pigmentation in many mammals. In both specimens it turned out to be a variant that is associated with fair skin and red hair. An artist has rendered a French Neanderthal man’s physiognomy from his skull, by combining this information with modern facial reconstruction techniques (in Culotta, E. 2007. Ancient DNA reveals Neandertals with red hair, fair complexions. Science, v. 318, p. 546-547). He seems set to become a pin-up among those ladies who favour the larger gentleman, even having a nose far larger than that of Gerard Depardieu. Although proof of the growing power of genetic analysis of ancient tissue, that Neanderthals were probably pale-skinned is not really surprising. They inhabited high latitudes for at least 200 ka longer than modern Europeans have, and the pale variant of mc1r is advantageous where sunlight is at a premium for creating vitamin D. Like modern Europeans, their immediate ancestors who migrated northwards were almost certainly dark-skinned.

Yet by far the most scientifically exciting outcome of the team’s work is the extraction from the Spanish Neanderthal bones of the FOXP2 gene, which is implicated in the development of speech and language (Krause, J. and 12 others 2007. The derived FOXP2 variant of modern humans was shared with Neandertals. Current Biology, v. 17, p. 1908-1912). It shares two mutations with FOXP2 in modern humans, that had previously been suggested only to have developed in the last 100 ka, so must have been present in the last common ancestor of fully modern humans and Neanderthals, around 300 to 400 ka. Although this discovery cannot prove that Neanderthals spoke, taken along with emerging evidence that symbolic skills were used by even earlier hominins (see When and where ‘culture’ began in November 2007 issue of EPN) it does suggest they were capable of as much sophistication as the earliest fully modern humans.

Is human evolution speeding up?

Another outcome of the acceleration in genetic analysis is an ability to scan vast numbers of differences in DNA from many individuals.  Highly productive are single nucleotide polymorphisms or SNPs (‘snips’) that are available from the international HapMap project. From analysing almost 4 million SNPs from 270 individuals has emerged an intriguing parallel between human population explosion since about 40 ka and an increasing rate at which new genetic traits have been incorporated into the human genome (Hawks, J. et al. 2007. Recent acceleration of human adaptive evolution. Proceedings of the National Academy of Sciences, v. 104, p. 20753-20758). The link is not entirely surprising, for the exposure of more individuals to mutagenic factors will result in more mutations entering the total gene pool. Yet ‘weeding-out’ of unfavourable mutations also operates over time, so the fact that around 7 % of human genes seem to have changed over the last 40 ka, indicates the overall rate of human evolution must have speeded up remarkably. The analysis suggests that the rate rose to a peak between 5000 and 8000 years ago, for Europeans and West Africans respectively. ‘Received wisdom’ has for a long while been that fully modern humans went through a phenomenal spurt in evolution around 50 to 40 ka (but see When and where ‘culture’ began in November 2007 issue of EPN), and that somewhat Eurocentric view is overturned by the SNP evidence. Selection pressures must have risen to a peak around the time of the spread of agriculture and the rise of large social communities – big changes in diet and in exposure to communicable disease would be associated with those shifts.

In some respects the findings are cause for optimism. Global warming and rapid transformation of climate belts will expose billions of people to new experiences. Hundreds of millions, or more, may perish, yet our species’ evolution may speed up again. Let’s hope it leads to some improvement in avoiding self-induced misfortune.

See also: Holzman, D. 2007. How we adapted to a modern world. New Scientist, v. 196, 15 Dec 2007 issue, p. 8-9.

The Afar Depression of Ethiopia, especially the middle reaches of the Awash River, has become world renowned as the cradle for early humanity. After the revolutionising discovery in 1974 in the Hadar area of the 3.3 Ma old Australopithecus afarensis remains that became known as ‘Lucy’, other finds – Ardepithecus, Orrorin and Sahelanthropus hit the headlines, pushing back the age of possible human ancestors to almost 7 Ma. None of these had Lucy’s degree of preservation, and the vital issue for the origin of humanity – bipedalism – could only be addressed by scanty evidence about the position of attachment of the cranium to the spine. Much else had to be inferred from teeth and facial shape, and odd bits of long limb bones. Lucy and remains of other A. afarensis individuals that rain progressively washes from the badlands of Hadar provide an embarrassment of riches by comparison. There is little doubt that could walk upright, but a question that has lingered is whether or not it also clambered habitually in trees. The other missing information is the vital one of development, for one big difference between apes and us is the grossly extended infancy of modern humans during which the attributes of consciousness, language and much else that is unique arise. To get a grip on developmental issues demands near-complete juvenile remains. The oldest infant fossils that come close are those of a Neanderthal child from 100 ka ago. A dramatic paper (Alemseged, Z. et al. 2006. A juvenile early hominin skeleton from Dikika, Ethiopia. Nature, v. 443, p. 296-301) brings the spotlight back to Middle Awash and to A. afarensis.

The drama has been long in the making. Zeresenay Alemseged, an Ethiopian working in Germany, made the initial find in 2000, collecting more material and painstakingly exposing bones from their sandstone matrix, grain by grain, over the last 5 years. The skull and dentition are complete, and bar the pelvis, lower spine and some limb bones, so is the rest of the skeleton. Morphology points unerringly to A. afarensis, and the stratigraphic position is the same as that entombing ‘Lucy’. Even without the inferences that can be drawn from it, preservation of a complete body is a near-miracle that ranks with that of the ‘Turkana Boy’ (H. ergaster) and ‘Lucy’. The entombing sediments are those of a small stream, which discharged to a large lake that occupied parts of the Middle Awash area during the Pliocene, so that the body was quickly enclosed in fine sands, possibly after the child was washed away in a flash flood. The jaws contain adult teeth waiting to erupt and, by comparison with chimpanzees, they suggest an age at death of about three years, although comparison with human children would probably give an older estimate. The shape of the adult teeth is similar to those of female, so the infant is a ‘she’. Much more work needs to be done on ‘Selam’ (Peace in Amharic), but that reported so far bears strongly on the issue of bipedalism. The shoulder blades and semi-circular canals of the ear, on which balance depends, are ape-like, and a finger bone is curved like that of a chimpanzee. ‘Selam’ was equipped for climbing, but she has leg and foot bones with more human affinities, which would enable upright walking as well. Being a near-complete individual, ‘Selam’ can be compared with whole adult A. afarensis specimens, notably ‘Lucy’, and with modern apes and humans, to assess the crucial issue of development that should throw light on just how close the species was to a transition to the human species that arose about a million years later.

Interestingly, the same issue of Nature includes a mini-biography of the Tunisian-born geologist Maurice Taib. He was the first to work on the terrestrial Pliocene sediments of the middle reaches of the Awash River, thereby opening to road to palaeoanthropolical fame for the likes of Don Johanson, Tim White and two generations of Ethiopian scientists, whom Taib played a major role in training and encouraging (Dalton, R. 2006. The history man. Nature, v. 443, p. 268-269).

See also: Wood, B. 2006. A precious little bundle. Nature, v. 443, p. 278-281. Wynn, J.G. et al. 2006. Geological and palaeontological context of a Pliocene juvenile hominin at Dikika, Ethiopia. Nature, v. 443, p. 332-336.

Drying East Africa

The 7 Ma recorded history of humans and their hominin ancestors was almost exclusively East African, until early members of the genus Homo began to migrate in pulses after about 1.8 Ma. Exodus from Africa on several occasions has been linked with climate change or the opening of routes by falls in sea level during periods of massive ice accumulation at high northern latitudes. Likewise, the evolutionary adoption of a bipedal gait by formerly forest-dwelling apes was probably driven by climate change that saw the spread of more open savannah ecosystems. Records from fossil assemblages in river and lake-bed sediments of East Africa, and from pollen in nearby sea-floor sediments do show a reduction in woodland cover and a spread of grasslands since the Upper Miocene (6 to 8 Ma) – the period of hominin adaptive radiation. Most workers on African climate change in the Neogene attribute the shift to cooling, either through a fall in atmospheric CO₂ or the onset of Northern Hemisphere glaciation. Yet East Africa has its own engine for climate and ecosystem change: the formation of the great Rift system and the uplift associated with it. While recognised as a climatic influence tectonics in the region has been downplayed by comparison with global shifts. That is surprising, since in the last 20 Ma, and perhaps more recently, what was an area of low relief has been transformed while rift shoulders rose to more than 3 km, from Eritrea in the north to Malawi 6000 km to the south.

Before rifting began, flood volcanism poured out a basaltic veneer in the late Eocene to mid-Oligocene, to achieve a thickness of more than 2 km in Ethiopia. Rather than creating high ground the flood basalts, being denser than continental crust, probably caused subsidence that roughly maintained low surface elevations. The achieved their present high elevations in the Ethiopian Plateau no earlier than the late Miocene. Large plateaux deflect low altitude winds and seem certain to have influenced climate on a regional scale, as did the Tibetan Plateau. The timing and pace of East African uplift remains poorly constrained, partly because geological evidence shows highly episodic tectonics, with periods of seeming quiescence between episodes of extensive and profound faulting and uplift, and partly because many of the rocks involved are sparsely dated. Yet the present topography and geological infrastructure are sufficiently well known that modelling any morphological influence on climate is possible.  By considering several plausible tectonic scenarios, a team of French palaeoclimatologists have modelled the possibilities (Sepulchre, P. et al. 2006. Tectonic uplift and eastern Africa aridification. Science, v. 313, p. 1419-1423). Their models show that uplift may have shifted atmospheric circulation drastically to establish the strong seasonality that dominates the region nowadays. Applying their results to likely ecosystems results in a pattern of decreased tree-cover.

While convincing, Sepulchre and colleagues’ work demands more precise timing for the establishment of sufficient tectonic topography. Nevertheless, it shows that events, arguably beginning at the core-mantle boundary, that triggered East Africa’s dominant tectonic influence, the Afar plume, probably conditioned our own eventual emergence.

A lot closer in time is an analysis of climate change in the Eastern Sahara desert since the end of the Younger Dryas (<12 ka) that devotees of the ‘English Patient’ will find revealing (Kuper, K. & Kröpelin, S. 2006. Climate-controlled Holocene occupation in the Sahara: motor of Africa’s evolution. Science, v. 313, p. 803-807. Being based on 150 archaeological excavations, the account of sudden humidity after 8.5 ka and then slow aridification since 5.3 ka is persuasive background to the rise of the pharaonic kingdoms of the Nile once nomadic Saharan pastoralism slowly became impossible.

Asian migrations reviewed

Sometime between 100 and 60 ka, fully modern humans found their way from Africa to the Far East and beyond. The timing and the issue of how many migrations were involved are topics in turmoil, now that genetic analyses help trace linkages among modern people. That was semi-popularised by Steven Oppenheimer’s The Peopling of the World (2003, Constable, London), which remains the genetically based ‘straw man’ of human migrations. Like Oppenheimer, Paul Mellars also of the Dept of Archaeology at Cambridge University, argues for single exodus and rapid eastward dispersal, but leaves open the route either via the Straits of Bab el Mandab or through Mesopotamia (Mellars, P. 2006. Going East: new genetic and archaeological perspectives on the modern human colonization of Eurasia. Science, v. 313, p. 796-800). While genetic lines of descent are a most powerful tool, any conclusions need confirmation through ‘hard’ evidence from excavations, and both Arabia and the India subcontinent are irritatingly blank in that regard.  However, there are a few coastal sites that whet the appetite.  As Jonathan Kingdon first suggested, in Self-made Man and His Undoing (1993, Simon and Schuster, London), the most likely routes for migrants would have been along the shoreline. ‘Strandlopers’ would have had easy pickings from littoral food sources, even during periods of aridity related to global cold spells. But there is the problem: with sea levels well below the present ones, most truly ancient sites will now be hidden below the sea. As regards the route taken, much depends on what the Nile valley has to offer archaeologically, for that is the natural way to the eastern Mediterranean and access to the Arab Gulf either across Syria or skirting the mountains of Kurdistan. The route across the Red Sea already has excellent support by the discovery by the Gulf of Zula in Eritrea of abundant evidence for habitation by ‘strandlopers’ around 100 ka.

Humans left Africa with a meagre tool kits at a remarkably early date, possibly around 1.9 Ma from finds of primitive stone tools in Pakistan and Central China, and certainly before 1.7 Ma in the case of the now celebrated human remains at Dmanisi in Georgia and in Java. Around 1.7 Ma sites with evidence for human occupation extend from southern to north-western Africa and over 2/3 of the width of southern Eurasia. Despite the increased chances of preservation in later times, such a wide-ranging expansion seems not to have recurred until the fully modern human diaspora from Africa that began around 70 to 100 ka. Fossil evidence suggests that descendants of these earliest known migrants thrived until as recently as 20 ka in south-east Asia, and perhaps longer, if tiny Homo floresiensis prove to be other than symptomatic of congenital dwarfism. They represent a puzzle, and absence of evidence has deterred palaeoanthropologists from sticking out their necks, until a recent review of possibilities (Dennell, R. & Roebroeks, W. 2005. An Asian perspective on early human dispersal from Africa. Nature, v. 438, p. 1099-1104).

For a long time all human remains dated between 1 and 1.9 Ma were ascribed to H. erectus, whose type specimen hails from Java, not Africa. Anatomical re-evaluation of specimens from Africa, notably the famous, 1.6 Ma old Turkana Boy from Kenya, shows that they are sufficiently different from Eugéne Dubois’s Javan H. erectus type specimen to warrant a different species name – ‘Action Man’ or H. ergaster. The Dmanisi humans have close affinities, but are older. Therein lies one puzzle: apart from the very much more primitive (and very rare) H. habilis of east Africa, there is no obvious African candidate as an ancestor for H. ergaster there. Dennell and Roebroeks speculate that they migrated back to Africa after evolving there from some unknown earlier species. Another puzzle centres on the tools carried by the early migrants from Africa.

Simple chopper and rough flake tools first appear in north-east Ethiopia at 2.6 Ma, but with no clear sign of who made them. The first discovery of the earliest known tool kit was at Olduvai Gorge in Tanzania – hence their name, Oldowan. They are associated with remains of the earliest known human species H. habilis, but date only to 1.8 Ma. Since Oldowan tool use is now known to have extended over a huge range of Africa and Eurasia at that time, the original emigrants must have carried the culture with them sometime after its first appearance in Ethiopia at 2.6 Ma. The emblematic artefact of ‘H. erectus’ is the beautiful pear-shaped biface axe, yet it first appeared at 1.5 Ma in Africa, and did not make an appearance outside the continent until about 700 ka and never made it to east Asia until carried their by fully modern humans: it was an African invention. Oddly, these highly crafted tools are often found with little sign of wear, and indeed opinion about what they were for is divided.

The great problem in palaeoanthropology is absence of fossils, which is hardly surprising. Dennell and Roebroeks comment that most Late Pliocene to Early Pleistocene terrestrial faunas are nearly always of large, robust animals, and even they are uncommon. The ravages of erosion and transportation also make it difficult to date finds of stone tools, as they may have been mixed with younger dateable materials. With confidence, they rely on the old adage (not well liked by the Popperian school of scientific methodology) that, ‘Absence of evidence is not evidence of absence’, and also that the earliest evidence for a new migrant is bound to be younger than its first presence. They look to the palaeoecological record of the period, which suggests a vast extent of open savannah covering much of Africa and southern Asia in the period when the climatic effects of glacial-interglacial cycles had not gripped low latitudes to create the desert barriers of later Pleistocene times. For species adapted to savannah life there was little to prevent their very wide migration, indeed simple diffusion would have moved them across the entire savannah range. Once thought to be confined to the East African Rift, australopithecines have turned up as far afield as modern Chad, 2500 km away, and as long ago as 3.5 Ma. If such diminutive creatures with no tools could diffuse so far, then what might have been the geographic limitation to the earliest tool users? Moreover, diffusion has no direction in the area that presents its possibility: movement could have been back and forth. An intriguing point made by Dennell and Roebroeks is that climatic instability first appeared around 2.6 Ma in Central China, so any emigrants moving north would have been subject to greater evolutionary-selective pressures for longer. Homo ergaster might have evolved in Asia and returned to Africa in the face of worsening conditions. This approach raises as many plausible hypotheses as a stick can be poked at, and should re-vitalise palaeoanthropological research outside Africa as a means of testing them.

Dee also: Kohn, M. 2006. Made in Savannahstan. New Scientist, v. 191 (1 July 2006 issue), p. 34-39.

Finds in Kenya, Ethiopia and Chad during the first few years of the 21^st century suggest that bipedal hominins, perhaps on the human clade, emerged as long ago as 7 Ma. Even using the previously accepted molecular-clock age for separation of chimpanzees and hominins, this is dangerously close to the time of the last common ancestor of both (5-10 Ma). Results from comparison of more detailed chimp and human genomics (Paterson, N. et al. 2006. Genetic evidence for complex speciation of humans and chimpanzees. Nature, doi:10.1038/nature04789, online) throw up a bewildering series of possibilities. On Patterson et al’s reckoning, our descent split from that of our nearest relatives no more than 6.3 Ma ago and perhaps as recently as 5.4 Ma, implying an overlap between tangible evidence and that based on DNA. Of even greater concern is the fact that human and chimp X-chromosomes are more similar than the rest, and seem to have diverged even later. One way in which this greater similarity could have arisen is if natural selection had been operating more strongly on X-chromosome genes, which studies of other related species show to have stemmed from hybridisation. Genes found on X-chromosomes that make hybrids less fertile can create strong selection pressures on this chromosome. An explanation that takes into account the young date of apparent splitting and strong selection operating on X-chromosomes is that the actual speciation(s) did take place before the time when the oldest hominin fossils were preserved, but that there was common interbreeding between the two closely related lines. 

Understandably, palaeoanthropologists and geneticists are arguing heatedly, but failing to recognise the great differences between fossils and extant genetic evidence: each is bound to tell a different part of the story. Yet another is the ecology connected to either lineage, the end point being a regional separation into creatures of forest and open savannah, separated by considerable distances in Africa – basically west and east of the East African Rift system. Before that climatic and vegetation-cover schism what would there have been to stop a great many branchings from either lineage of very closely related animals? The rarity of fossils from either may leave the true relationships early in the history of both clades completely impenetrable. One thing is for sure, although chimps and humans today do make close friendships, that is as far as it goes…

See also: Holmes, B. 2006. Did humans and chimps once merge?. New Scientist, v. 190 20 May 2006, p. 14. Pennisi, E. 2006. Genomes throw kinks in timing of chimp-human split. Science, v. 312, p. 985-986.

Hobbit matters

Debate about the significance of the tiny hominid fossils from the Indonesian island of Flores (H. floresiensis) continues to escalate. The remains are sufficiently complete for analysis of other things than size and morphology of skull and brain. It seems that the shoulder structure is different from that of modern humans, but more similar to that of full-sized H. erectus (see Culotta, E. 2006. How the hobbit shrugged: tiny hominid’s story take a new turn. Science, v. 312, p. 983-984). In ourselves, when standing straight, our inner elbows face slightly forwards so that we can work with both hands in front of the body. The necessary twist in the humerus is somewhat less in H. floresiensis, and by itself that would inhibit being able to make tools. However, the shoulder bones of the fossil articulate differently with the hobbit humerus so that a hunched posture would allow intricate work, but not an overarm throwing action. Much the same features characterise the well-preserved upper bodies of H. erectus fossils from Africa and Georgia. Incidentally, like J.R.R Tolkien’s fictional Hobbit, H. floresiensis also had disproportionately large feet.

It seems inescapable that H. floresiensis did make tools. As well as the 90-12 ka artefacts found in the Liang Bua cave with the hominid remains, which some have reckoned to be too complex for the small people to have made the, large numbers of similarly sophisticated stone tools have been found at other sites in Flores. These occur with similar prey species, but not hominid remains, from as long ago as 800 ka; a time at which only H. erectus was present in the Indonesian archipelago (Brumm, A. et al. 2006. Early stone technology on Flores and its implications for Homo floresiensis. Nature. V. 441, p. 624-628).

The minute size of H. floresiensis, with a brain capacity of a mere 400 cm³, continues to cause some researchers to doubts that the fossils – in fact 9 sets of remains from Luing Bua – were other than congenitally deformed modern humans: microcephalics. Anatomist Robert Martin of the Chicago Field Museum of Natural History (see www.sciencemag.org/cgi/content/full/312/5776/999b) used scaling factors of other dwarfed mammals from island faunas to model the body versus brain size to be expected for similarly dwarfed hominids that might arise from isolated H. erectus. He calculated that the 400 cm³ brain of H. floresiensis should be associated with a creature with around 11 kg body mass: about the size of small monkey. But that conflicts with the fact that the famous skull shows no signs of other deformities associated with microcephaly (See Culotta, E. 2006. How the hobbit shrugged: tiny hominid’s story take a new turn. Science, v. 312, p. 983-984).

From the late 19^th century it has been clear that two species of our genus Homo inhabited Europe and the Middle East: modern humans and Neanderthals. Recent partial sequences of Neanderthal genetic material, compared with the human genome, confirm that the two did not interbreed; at least, no trace of Neanderthal genetics remains in that of modern humans. The discovery in Indonesia that fully modern immigrants occupied the same territory as Homo erectus from 70 to 20 thousand years ago adds more weight to the hypothesis of multiple occupancy of the world by different kinds of humans until recent times. The astonishing discovery in 2003 of the remains of tiny hominids (Homo floresiensis) on Flores whose occupancy lasted from at least 840 ka to as recent as 12 ka (see The little people of Flores, Indonesia, November 2004 issue of EPN) confirms mixed occupancy late in hominid evolution. That includes several different representatives of Homo – habilis, eragster and erectus – and also paranthropoids in Africa around 2 Ma years ago. As regards Homo, this cohabitation, especially that in Africa, supports two hypotheses: that our lineage was bush-like and involved separate extinctions and sudden appearances of new species (cladogenesis), or that the great variability in physiognomy (polymorphy) of modern humans extended back for a considerable time. The second is the view of Jonathan Kingdon, who believes insufficient hominid fossils have been collected to rule out polymorphism among tool-using and tool-creating beings. The idea of a single lineage since the first appearance of bipedal apes that led unerringly through gradual changes to modern humans (phyletic evolution) has been largely discarded. For at least part of the 6-7 Ma hominid record, that abandonment of phyletic evolution may have to be reconsidered, following a report of remarkably productive excavations in the Awash Valley of NE Ethiopia (White, T.D. and 21 others 2006. Asa Issie, Aramis and the origin of Australopithecus. Nature, v. 440, p. 883-889).

The Middle Awash is the single most productive area for hominid remains and other fossils that help establish changes in their environment. That is so because of consistent collecting for more than two decades by a multinational team, co-led by Ethiopian and US palaeoanthropologists, from a sequence of flood plain sediments over 1 km thick, liberally interlayered with dateable volcanic horizons. Its middle parts record three species, Ardepithecus ramidus, Australopithecus anamensis and Australopithecus afarensis (of which ‘Lucy’ was a member), in an age range from 4.42 to 3.88 Ma. White and the other members of the team have unearthed 30 new fossils of all three species, but, so far, no examples of more than one in a particular thickness of sediments. Of course, ‘absence of evidence is not evidence of absence’, but this massive addition to the Pliocene hominid record is a challenge to the prevailing hypothesis of cladogenesis – Steven J. Gould’s idea of punctuated equilibrium, in which species arise by sudden appearance of new characteristics from earlier ancestors. Its test is whether or not ancestral species co-exist with new species for a time. In the Middle Awash, it seems that they do not, even though the critical 300 m of sediments represents only 200 thousand years.

The three species, and their predecessor Ardepithecus ramidus kadabba (5.5-5.8 Ma), show variations in their teeth, with Ar. r. kadabba and Ar. ramidus sharing some similarities, and Au. anamensis and Au. afarensis others. The shift between the two sets of common dentition can be explained by either gradual changes in a single lineage over about 2.5 to 3.0 Ma, or a sudden speciation event, perhaps around 4.5 Ma. The lack of overlap favours the first hypothesis. Complicating factors are rife, however, for there may have been migrations (Ar. Ramidus is known from far to the south in Kenya), and yet more evidence will undubtedly be found from the vast amount of sediment of this age in the Afar Depression.

See also: Dalton, R. 2006. Feel it in your bones. Nature, v. 440, p. 1100-1101.

Palaeodentistry

Those of a nervous disposition should not read this item.

A 7500 to 9000 year-old Neolithic graveyard in Pakistan has yielded remains of about 300 people who cultivated wheat, barley and cotton, and herded cattle. There is nothing remarkable in that, except that nine individuals have teeth that have clearly been drilled neatly (Coppa, A. et al. 2006. Nature, v. 440, p. 755). The holes are between 1-3 mm in diameter and up to 3.5 mm deep, and would have exposed sensitive parts of the tooth. In excavations of the nearby village of Merhgarh are found tiny flint drill heads associated with beads of various ornamental materials. The drills are of the same size as the tooth holes. Quite probably, miniature bow-drills tipped with flint would have been used by Neolithic dentists for at least 1500 years – there is no evidence for tooth drilling from younger cemeteries in the area, despite abundant evidence of dental decay. Experiments show that such drills would take less than a minute to produce the neat holes, probably wielded by jewellers rather than dentists.

Asian Homo erectus skilled in tool making

The 1.8 Ma emigrants from Africa who first populated the Far East have not been regarded as having been especially inventive. While their ‘cousins’ in Africa developed the aesthetically stunning bi-face axe about 1.6 to 1.4 Ma ago (the first instance of visualising a finished object within a rough piece of raw material), H. erectus in East Asia is associated with the most primitive stone tools made by simply breaking flinty stones. That seemed to have been the extent of their stone-using skills up to their final demise about 20 thousand years ago –not a lot of progress in 1.8 million years. A report in March at the Indo-Pacific Prehistory Association Congress (Manila) of yet to be published work by Harry Widianto of Indonesia’s National centre of Archaeology may force a revision of this less than charitable view of early Asians (Stone, R. 2006. Java Man’s first tools. Science, v. 312, p. 361). In the Solo district of Java, made famous by Renée Dubois who found the first fossils of H. erectus there, a wealth of finely worked flake tools has been discovered in sediments that are about 1.6 Ma old. Most are small and made from blood-red to beige, translucent chalcedony. It seems that necessity was the mother of invention in this case, because suitable materials for sharp tools are very scarce in Java.

About 4200 years ago early civilisations of the Old World underwent decline and collapse. Examples are the Akkadian civilisation in the upper Tigris and Euphrates basins, famed for Hammurabi’s Hanging Gardens of Babylon, the Harappan of the Indus Valley (Mohenjodaro), the phaoronic Old Kingdom and the Minoan of Crete. This period of the Bronze Age has been thought by some to have experienced either massive volcanism – the explosion of Santorini – or even a comet strike. Others have correlated collapses of city states with Biblical events. Whatever happened, its outcome spanned a vast area of western Asia and north-eastern Africa, so another candidate is climatic drying leading to drought and famine. That is perhaps not such a spectacular fate as near-instant environmental upheavals, but probably just as effective for societies dependant on regular agriculture production or, in the case of Crete, on wide-ranging trade.

Detecting climate change is now well established on proxy records of one kind or another, such as those based on isotopes and sedimentation changes from sea-floor sediments and flowstone (speleothem) in caves, and dust records in ice cores. Such time-series from the mid- to late Holocene are increasing in number, with particular interest growing in records from speleothem now that precise age sequences are possible using uranium-series dating. A flowstone record from a cave in northern Italy, has helped link other time series ranging from the North Atlantic floor, in the Middle East and East Africa (Drysdale, R. et al. 2006. Late Holocene drought responsible for the collapse of Old World civilizations is recorded in an Italian cave flowstone. Geology, v. 34, p. 101-104). A team of geochemists ad environmental scientists from Australia, Italy and the UK has shown a remarkable coincidence among these widely different records, centred on 3900-4200 b.p.. From the North Atlantic at high latitudes is an upsurge in fragments deposited by ice rafting, while mean sea-surface temperatures swung downwards. Kilimanjaro ice shows a marked peak in atmospheric dustiness. Carbonate deposition peaked in the Gulf of Oman. Finally, the Italian flowstone shows peaks in d¹⁸O, d¹³C and the magnesium:calcium ratio of its carbonates. The conclusion is a period of climatic cooling and drying that spanned 40 degrees of latitude over a period of several hundred years. This is not the signature likely to have been associated with instantaneous catastrophes. Yet nor is it typical of the episodic climate shifts of the order of a few thousand years, which were now well known features of the last glacial period and the current interglacial. It was certainly sufficiently prolonged and large enough to have wrought havoc on early civilisations, and throughout the Old World it clearly did.

Culture in the most general sense that encompasses tools, clothing, habitation and fire has increasingly set humans and their ancestors apart from the rest of the natural world. It might therefore seem that becoming more ‘human’ cushions our line from Darwinian natural selection since we have created our own ‘nature’ and carry it with us. Setting fully modern humans adrift in the environment, without that culture, would undoubtedly result in rapidly extinguishing the species. In that hypothetical context we are far from ‘fit’, in Darwin’s sense. However, the development of humanity’s cultural milieu has itself provided a continually changing, increasingly pervasive artificial set of conditions for natural selection. Culturally, the most dramatic step in human evolution, for which we have tangible evidence, emerged with the explosive appearance of graphic art and a complex ‘toolkit’ around 35 thousand years ago in Europe. That huge advance will undoubtedly be traced back maybe tens of millennia when archaeological finds in Africa and Australia, for instance, are more precisely dated.  Evidence from the DNA in male-carried Y chromosomes indicates that a profound genetic shift occurred around 70 ka, perhaps resulting from a decline in global human numbers to a very small population after the climatic disaster wrought by the explosive eruption of the Toba volcano in Indonesia. That too was a time when fully modern humanity distributed itself more thinly by a decisive exodus from Africa. Some specialists have speculated that the cultural explosion stemmed from that evolutionary ‘bottleneck’.  There are genetic signs of adaptation to cultural practices and selective pressures that accompanied them after the rise of agriculture and settlement (See Has human evolution stopped?, September 2005 issue of EPN). Recent work on the whole human genome gives an inkling that even more pervasive evolutionary changes took place in the last 50 thousand years (Wang, E.T. et al., 2005. Global landscape of recent inferred Darwinian selection for Homo sapiens. Proceedings of the National Academy of Science, www.pnas.org/cgi/doi/10.1073/pnas.0509691102).

Wang and colleagues from the University of California studied the occurrence of single-letter differences in the genetic code (single-nucleotide polymorphisms – SNPs). Scattered across all human chromosomes are about 1.6 million of these SNPs. They appear not to do anything, but can be linked to nearby genes. When natural selection favours a particular mutated variant of a gene, the associated SNPs can be selected as well. The approach used by Wang et al. is a statistical search for pairs of SNPs that occur together more often than could be possible by chance ‘reshuffling’ that occurs from generation to generation. Their analysis suggests that around 1800 genes, a remarkable 7% of the whole genome, have changed over the last 50 thousand years. Interestingly, that is similar to the degree of genetic change in maize since its domestication from its wild ancestor. As well as genes connected to protein metabolism that could have changed as new diets followed the rise of agriculture, some that are involved in brain function have been selected as well.

Although at an early stage, this kind of research confirms that we are indeed still evolving along Darwinian lines, perhaps unwittingly domesticating ourselves. It is easy to assume that ideas, skills and artistic sensibilities are passed on through language and learning and thereby grow and diversify, but in order for any of these to stimulate the deep feelings that they foster suggests that some aspects have become ‘hard-wired’ in all of us. Everyone unconsciously taps their feet to rhythm, can be moved to a vast range of emotions by music, words and visual stimuli, and can ‘sense’ an environment captured, even in abstraction, by a talented artist. They inspire further development. Until around 50 ka human culture, insofar as we can see evidence for it, remained fixed for more than a million years through several species and subspecies of the genus Homo. Appearing between 1.6 and 1.4 Ma ago the bi-face stone axe endured as humanity’s highest known achievement until those very recent times.

See also: Holmes, R. 2005. Civilisation left its mark on our genes. New Scientist, 24/31 December 2005 issue, p. 8.

Earliest tourism in northern Europe

Some years ago British palaeoanthropologists were in a state of high excitement about finds of stone tools, evidence of prolonged human habitation and fragmentary skeletal remains from a sandpit at Boxgrove on England’s southern coast.  They showed the earliest human presence at high latitudes around 400-500 ka. The date of early colonisation has now been pushed back more than half as long before that to 700 ka by finds in a shoreline exposure of riverine sediments on the coast of Suffolk on England’s east coat.  The Cromer Forest Bed of Middle Pleistocene age has been know since Victorian times as a rich source of the flora and fauna from one of the earliest interglacials of the current period of 100 ka climate cyclicity. At that time the North Sea had yet to establish a connection that would eventually separate the British Isles from Europe, and the site at Pakefield would have been the estuary of a now-vanished river system draining the Midlands and Wales.  So far no human bones have turned up in the excavations, which have to be conducted at low tide. But many flint tools pepper the organic-rich sediments (Parrfitt, S.A. et al., 2005. The earliest record of human activity in northern Europe. Nature, v. 438, p. 1008-1012). As with most terrestrial deposits, establishing the age of human occupation posed the greatest difficulty. A careful documentation of magnetic polarity combined with fossils – including distinct voles – and a new technique that relies on assessing the degree of protein degradation in bivalve shells helped tie-down the age precisely.

Around 800 ka human occupation had begun in Spain and the Pakefield site shows that migration northwards of flora and fauna following a glacial epoch was swift, to establish conditions considerable warmer than in the Holocene. It seems that this Mediterranean climate encouraged such northward penetration by humans, most likely during a short period of particular warmth. Long eyed by archaeologists as a potential source of human remains, patience has paid off in the Cromer Forest Beds.  Yet around the world there are many other, equally promising strata or Pleistocene age that have not had such undivided attention for so long, A glance at the distribution of keynote sites for palaeoanthropology shows how narrow the search for human origins and migratory destination has been up to now. Though it is understandable that once finds have been made, funds and scientists cluster where progress is best guaranteed. Very rarely, either a ‘shot in the dark’ pays off or something surprising turns up at a site being excavated for other purposes. Broadening the search may well have high financial and career risks, yet the more discoveries are made at well-trodden sites the greater the likelihood that the full story of human evolution and migration will be revealed by breaking new ground,

See also: Roebroeks, E. 2005. Life on the Costa del Cromer. Nature, v. 438, p.921-922.

Biogeochemical evidence for vegetation change when hominins evolved

A long-held theory that concerns the background to hominin evolution, is that the freeing of hands by bipedalism was triggered by a shift in the ecology of East Africa from forest to more open grassland.  That might well have happened as the Neogene uplift associated with development of the East African Rift transformed the regional wind and rainfall patterns to the way they are today, thereby creating the conditions for the modern savannahs and semi-deserts in the area long associated with human origins.  The lakes of East Africa are ephemeral in the context of Neogene climate change, and so their sediments are not much use in charting long-term shifts in flora.  However, the modern wind systems shift dust and organic particles consistently towards the Gulf of Aden, so sediment cores there potentially provide a continuous record of vegetation change.  That is, if they contain ‘biomarkers’ that distinguish the debris of trees from that of grasses. The first biomarker records from the Gulf of Aden seabed powerfully confirm the notion of vegetation change as a possible driver for hominin evolution (Feakins, S.J. et al., 2005. Biomarker records of late Neogene changes in northeast African vegetation. Geology, v. 33, p. 977-980).

Up to about 3.5 Ma the cores contain plant-derived waxes that are characteristic of trees that use C3 metabolic processes, but thereafter evidence for increasing C4 grasses predominates.  Coinciding with that broad trend is an increase in ¹³C in soil carbonates on land, which probably reflects increased grassland too.  Although records of hominin diversity before about 3 Ma are scanty, later times saw the rise of several bipedal species, grouped as the powerfully jawed parathropoids and the more daintily chewing members of the lineage that led to modern humans. Detail in those sections of marine core that were used – presumably costs prevented continuous measurements – shows that the carbon-isotopic signals in the waxes varied in harmony with evidence for climate change, so the proportions of savannah and woodland probably shifted quite rapidly.  However, because cold-dry periods have tended to be longer than those which were warm and more humid, savannah would have had more influence over faunas than ephemeral woodland. Fascinating as this empirical relationship between hominin evolution and vegetation change is, what Africa lacks – as indeed does most of the planet – is data that chart accurately how topography has changed with time. Cosmogenic and U-Th/ He apatite thermochronology, on which so much hope and funding have been invested, has proved spectacularly ineffectual compared with careful work on the likely effects of changing landforms.

Sitting on top of the Kremlin in Red Square is a huge five-pointed red star that is illuminated at night.  This is not just a relic of Stalin’s Soviet Union, but has its origins in a common myth that shows up concretely in archaeological digs, particularly in the Middle East, in the form of collections of fossil sea urchins and starfish. They, of course possess the five-fold symmetry unique to the Echinodermata, which also figures in the emblematic pentagram of Denis Wheatley’s awful novels about satanism and on the pointed hats of latter-day wizards and warlocks. I learned of this fascinating link between geology and symbolism at a session on Geology and Mythology at the 32^nd International Geological Congress in Florence (August 2004). This branch of geoscience seems destined to thrive, and Kevin Krajik has helped ensure that it does by reviewing a range of geo-inspired myths (Krajik, K. 2005. Tracking myth to geological reality. Science, v. 310, p. 762-764). His examples range from Pitman and Ryan’s hypothesis linking the flood myth of the Near East, first recorded in the Epic of Gilgamesh, to catastrophic filling of the Black Sea basin as sea level rose and spilled through the Bosporus around 7600 years ago, to the Oracle of Delphi. The most interesting and useful are those myths that incorporate an implicit warning of risk. Among these are pictograms of two headed serpents US which are reputed to shake the ground by native people of the NW who carved them. These a’yahos are found around major active fault zones. Cameroonian taboos include some that relate clearly to exhalation of carbon dioxide from crater lakes, as happened with disastrous effects at Nyos in 1986. The seafaring Moken of western Thailand have a tradition that a rapidly falling tide presages a man-eating wave: no Mokens died during the 26 december 2004 Tsunamis, despite living on the shore that was badly hit.

Various shenanigans within the Indonesian palaeoanthropology community have hindered evaluation of all the evidence surrounding the diminutive adult female skeleton found in Liang Bua cave on Flores in 2003.  Her skull was damaged after prolonged examination by a leading national figure in the science, and now further excavation in the cave has been blocked indefinitely. Whether she is indeed a member of new species of hominin, Homo floresiensis, or merely an individual modern human dwarfed by some genetic defect, as some claim, seems closer to resolution (Morwood, M.J. and 10 others 2005.  Further evidence for small-bodied hominins from the Late Pleistocene of Flores, Indonesia. Nature, v. 437, p. 1012-1017). During the 2004 field season at Liang Bua the Australian-Indonesian team unearthed remains of nine other individuals of similarly diminished stature. They included another jaw bone that is virtually identical to that of the first ‘hobbit’: neither have the chins that unify all fully modern humans.  Significantly, the new piece of lower jaw is dated at some 3 ka older than the original, so the chances of both being from physiologically unfortunate modern humans are remote.

The new finds also include stone tools, more advanced than any found in association with one of H. floresiensis’s possible ancestors, H. erectus.  Whoever they were, the ‘hobbits’ also butchered prey and cooked meat.  There is negative evidence in support of the new species hypothesis too: compared with human sites of the Late Pleistocene, Liang Bua is conspicuously lacking in evidence for any form of art. But the idea is not proven.  It would take a definite association between fossils and tools, as for instance in a burial, to show that the implements belonged to ‘hobbits’ rather than having been introduced by a fully human visitor. Moreover, should any evidence for moderns be found in Liang Bua or other caves of interest, the possibility of mixture of cultures and fossils would leave things up in the air.

It is worth noting that Indonesian scientists are not the only ones prone to obstructive tactics as regards hominin sites. They have long been a bone of contention throughout Africa, where both local and visiting scientists have tried to throw spanners in their colleagues’ research ambitions.

See also: Dalton, R. 2005. More evidence for hobbit unearthed as diggers are refused access to cave. Nature, v. 437, p. 934-935; Lieberman, D.E. 2005. Further fossil finds from Flores. Nature, v. 437, p. 957-958.

Congenital disease, human migration and population growth

The way in which genetic features are inherited has become a key feature in distinguishing human populations, the time and route of their migrations as separate groups, and when they merged with other groups.  The most familiar outcomes are those based on mitochondrial DNA and lines of female descent that show with little room for manoeuvre, that all of us descend from Africans alive around 150 to 200 ka.  Studies of the male Y chromosome help fine tune the record to show short periods when either populations fell so low that human survival passed through only a few small bands (e.g. around 70 ka) or Big Men corralled most women for their own purposes (the now famous case of Ghengis Khan’s genes still dominating the genetics of Central Asian people). Dennis Drayna of the US NIH outlines yet another revealing feature of genetics with historical connotation in the October 2005 issue of Scientific American (Drayna, D. 2005. Founder mutations. Scientific American, v. 293(4), p. 60-67).

Disabling congenital diseases, such as cystic fibrosis and sickle-cell anaemia, together with adverse reaction to alcohol and the ability of adults to tolerate the lactose in milk, are all passed down generations in different ways. Understanding the genetic processes involved obviously stems from medical research on genetic mutations so as to identify groups that are at risk.  From it has emerged details on the structure and location of the responsible genes in chromosomal DNA.  The feature that unites the four examples above is a special repetition of the same kind of mutant structure. Inherited conditions involve either different mutations in a single gene, or the identical change at a specific location.  Of the latter, it seems the most common is an innate tendency in DNA for the same mutation to affect a specific gene – so called ‘hot-spot’ mutation, which occurs in unrelated individuals.  More rare is a defect that is embedded in a length of DNA (a haplotype) whose structure is identical in all those who carry the mutation. That common identity suggests that the mutation arose once and has been passed down subsequently; a ‘founder’ mutation.

Since a ‘founder’ mutation arose at some time in the past it can potentially be used to trace population history, and so passes into the realm of palaeoanthropology. The fascinating and most useful feature is that the greater the separation in generations from the individual in whom the mutation occurred, the more restricted becomes the haplotype, in terms of its relative length in DNA.  That phenomenon is a consequence of sexual recombination among descendants.  In the founding individual, the whole chromosome is the haplotype, and the mutated part becomes increasingly ‘diluted’ with time.  Measuring its length today harks back to the time of foundation.  What has become clear is that not all founder mutations have any obvious consequence, and instead of being in as few as one millionth of a population, the general case for those causing disability and therefore conferring an adverse effect on natural selection, a few percent of people can carry them. Such abundance indicates either neutral effects or some subtle benefit to fitness.  Diseases ascribed to them appear when both parents contribute the mutation: most are recessive. 

A good example is a mutation of the HFE gene that confers above normal iron absorption, which is a decided advantage in protection against anaemia from iron-deficient diet.  An individual with two copies vastly overcompensates and iron accumulates to deadly levels in their cells.  Studies of its incidence in global populations indicate that it arose in Ireland, western Britain and Brittany and then spread south-eastwards. It appears to be a Celtic trait, although not from their original heartland in Central Europe but at the limit of their original migration more than 2000 years ago. Its haplotype is quite long and suggests a founder around 800 AD.  There are no records of significant late Celtic migrations, and quite possibly the spread was through wide-ranging Vikings who dominated parts of the western British Islands at that time. A more fascinating case is the founder mutation that prevents people who carry it from tasting bitterness.  Most people do experience bitter tastes, and that is very handy for avoiding toxic plants.  About 25% do not.  Maybe the mutation involved conferred some advantage, but the fact is that the haplotype is exceptionally short, representing a foundation at about 100 ka.  It occurs in Africa along with 6 variants of the bitter-taster gene, yet beyond that continent only one taster and the non-taster forms occur commonly.  That tallies with the hypothesis of the major movement out of Africa to populate the rest of the world with modern humans, around 75 ka ago. The surveys go intriguingly further: should descendants of those African migrants have bred successfully and regularly with earlier Eurasian hominins (Neanderthals and Erects), then non-African versions of the bitterness detecting gene ought to be present among non-African populations.  Not one ‘alien’ haplotype has been detected, and this novel approach seems to have lain to rest that particularly intriguing bit of sociology.

 

One clear character of the record of investigations into human evolution is that, rather than becoming clearer as data increase, our origins become more of a puzzle. With every major fossil find the hominin clade or bush of descent acquires what appears to be another branch. With the recent publication of the genome of our closest living relative, the chimpanzee – and its earliest fossil remains – (Nature, v. 437, p. 47-108), it will hardly be surprising if the assumptions about a gene-based time of separation of the two clades (5-7 Ma) comes into question. Studies of the Y-chromosomes of living human males have suggested ‘bottlenecks’ in our recent evolutionary past, interpreted to indicate near-catastrophic declines in numbers to perhaps that of a few scattered bands. One such ‘near-extinction’ seems to have occurred about 70 thousand years ago, which has been linked to the huge explosion of the Toba ‘supervolcano’ in Indonesia in whose ash are poignantly preserved biface axes. Toba would have had a global climatic effect at a time when fully modern humans were migrating rapidly from Africa across Eurasia; thinly spread and easily isolated by disaster. What followed was an explosive development of both material and aesthetic culture, perhaps enabled by some serious selection amongst those who endured Toba’s global blast.

It is always tempting to restrict hypothesizing with the ‘Just gimme the facts’ outlook – as people of my generation will remember from the main detective in the Dragnet TV series. That is, ideas based on hominin remains alone. Yet all evolution takes place within a wider environmental context; for much of our history that of East Africa. Scanty knowledge of tropical climates there and a reliance on distant deep-sea records had led to the widespread belief that this centre of most hominin evolution gradually became drier since the late Miocene. Lake beds in the East African Rift system have held the key to a useful record, and now some of the detail is emerging (Trauth, M.H. et al. 2005. Late Cenozoic moisture history of East Africa. Science, v. 309, p. 2051-2053). Lakes in the Rift are handy for climate study because they span 8 degrees of latitude north and south of the equator, the spread helping to isolate more local effects of volcanism and tectonics on their sedimentary record from those of regional climate change. Many have little outflow and a local supply of water, so their levels depend mainly on the amount of local precipitation compared with evaporation. The actively subsiding basins in which they form have the opportunity to preserve unbroken, thick records of both lake and river sediments.

Trauth et al. compile environmental and chronological information from sediments in seven Rift basins, going back to about 3 Ma. Volcanic events provide plenty of dating opportunities to calibrate and correlate the sedimentary evidence. They show three rift-long episodes of deep lakes spanning broad periods from 2.7-2.5, 1.9-1.7 and 1.1-0.9 Ma. A few sections reveal lake-level fluctuations on Milankovich timescales. The longer episodes link in time to the intensification of Northern Hemisphere glaciation, to a shift in east-west air circulation over Africa and to the switch from the dominant glacial cyclicity of 41 ka to one of 100 ka, respectively. Wisely, they consider the climatic information to be crucial to studies of human evolution, but still too coarse to be used with confidence in relation to details of the fossil record. Long humid periods would have been ‘easy’, whereas the separating drier periods may have experienced ups and downs in humidity on Milankovich timescales. Fluctuating conditions would have been more stressful and likely to witness speciation. One very odd feature is that the 1.9-1.7 Ma period of deep rift lakes is the time when H. erectus became the first tooled-up being to migrate far beyond Africa. Many have regarded migration as a response to environmental stress, but just as likely is an expansion of opportunity.

There can be no doubt that the way in which humans consciously build ‘shields’ of many kinds between themselves and their surroundings placed our species, and those leading up to it, in an increasingly different relationship to the environment than those of other organisms. Fire, habitations, tools, weapons and clothing emerged far back in our evolutionary ‘bush’, to be followed more recently by artificial means of feeding ourselves in a vast range of climatic conditions. In the last century these ‘shields’ have been added to by medical protection against pathogens.

Many of the physical traits of the modern human frame would not be ‘fit’ in a purely Darwinian sense for life unprotected by myriads of cultural devices: they arose from genetic potential largely because growing human culture allowed them to be fit for purposes other than survival at its simplest level. The range of basic physiognomies among modern humans does seem to reflect natural selection to suit various climatic regions, such as the differences between cold- and heat adapted peoples. That perhaps began during the great expansion out of Africa some 70 ka ago. But the much greater range of facial characteristics among all populations (a really human characteristic compared with other primates) is probably a result of genetic drift at random, rather than any kind of evolutionary selection. There are also differences that have arisen since the widespread adoption of agriculturally produced foods since about 10 ka ago, as in jaw shapes and those of the skull, probably linked to easier mastication. That can be explained most easily by the manner in which the use of muscle tends to sculpt the bone to which it is attached: it arises during the life of the individual.

With what appears to be the start of a global unification of cultures, and greater security for the more fortunate one third of humanity at least, it might be expected that natural selection is on the wane for humans. A mere 10 thousand years since the rise of agriculture and far less since modern cultures arose, it is perhaps too soon to conclude that we have cut loose from Darwinian processes. Indeed, recent genetic research has come up with several developments that must be recent results of natural selection. One is the split between adults who can metabolise cows’ milk and those who cannot. The first group, a minority, cluster around the Near East (most Europeans) and in a few parts of Africa where cattle domestication arose. A large block of the human genome, about a million base pairs of nucleotides, includes the gene that produces the necessary enzyme lactase, and its persistence in those adults able to digest milk. The large size of the whole haplotype is typical of recent genetic developments, and the researchers are certain that it resulted from selective pressure where dairy farming began at between 5-10 ka.

Genes that confer resistance to infectious diseases that can cut life short before successful reproduction are good candidates for showing the effects of natural selection, especially in those areas where medical care and drugs are not available. For a long while natural resistance among some west Africans to malaria parasites was linked with heritable sickle-cell anaemia, but recent research has shown a more complex reason that involves several genes. Interestingly, ‘dating’ of the associated genetic changes gives recent ages between 3 and 6 ka, perhaps linked to the rise of farming practices. Clearing land and ponding of water on fields would have encouraged the malaria-carrying Anopheles mosquitoes, which are not forest species: a cultural change presaged a genetic one. Similar results have emerged from studies of inherited protection against HIV/AIDS, yet that only appeared in pandemic form very recently (unless misidentified earlier). An explanation may centre on selective pressure on mutation to form the protecting gene as a result of the appearance of previous epidemics, such as plague and smallpox among early Europeans, who seem to have the highest resistance to HIV/AIDS.

So it is hard to say if selective pressures will work in future on the human genome, as culture convergence continues, and (hopefully) equitably shared living standards. Since the limit on human brain size is the skull, and that is limited by the near-maximum pathway through the human female pelvis, it is very difficult to imagine our evolution into big-heads.

Source: Balter, M. 2005. Are humans still evolving? Science, v. 309, p. 234-237.

Tool making hominid species left their African homeland several times in the past, the earliest being shortly after the appearance of Homo erectus, about 1.8 Ma ago.  Those early migrants ended up in eastern Asia, where they thrived until as recently as 12 thousand years ago (if indeed H. floresiensis does prove to be a miniature erect).  Europe was reached by at least three waves: possibly advanced H. erectus around 0.5 Ma; Neanderthals as early as 0.25 Ma; modern humans around 40 thousand years ago, at the earliest.  The fully modern human record in Asia begins at 67 thousand years ago, suggesting an exodus from Africa at between 80 and 70 thousand years.  There is an oddity here: simple geography suggests that Europe should have been colonised first in each wave out of Africa, because it is closer.  But the Nile to Middle East to Europe route was not successfully used by our immediate forebears until long after they moved eastwards, although there is evidence of H. sapiens temporary occupation of parts of Palestine between 100 to 80 thousand years.  Several reasons for this have been suggested, including the possibility of direct competition with Neanderthals who occupied the same 100 ka sites in the Middle East, and the relative difficulty of passage along the Nile compared with a coastal route in NE Africa. 

Eritrean and US archaeologists have shown that around 100 ka the Eritrean coast was occupied by humans who subsisted on seafood: always available whatever the climate, whereas terrestrial game potential fluctuates.  That has led to the suggestion that Africans who colonised Asia and Australasia left by island hopping across the narrow Straits of Bab el Mandab when sea-level began to fall around 70 ka.  A coastal route, well stocked with food items would have allowed rapid movement eastwards.  That seems intuitively likely, because an eastward route through the Middle East is barred by deserts, which would have been even more arid as glacial conditions developed.  Moreover, a Middle Eastern route would have led more directly to Asia Minor and ultimately Europe.  The conundrum deepens, since the Straits of Bab el Mandab would have been even easier to cross at the time of the last glacial maximum, around 20 ka, yet there are no archaeological signs of populations of that age in Yemen and Oman; research has hardly begun there.  Unravelling routes is possible, just, by analysing modern population genetics (Macaulay, V. et al. 2005. Single, rapid coastal settlement of Asia by analysis of complete mitochondrial genomes.  Science, v. 308, p. 1034-1036).  People living in the Andaman islands and the Malaysian Peninsula include groups who differ substantially from their neighbours and may be descendants of the original colonisers.  Mitochondrial DNA from these groups indicates a branching from an original type around 65 ka, remarkably suggesting a single founding woman.  That cannot be taken exactly at face value, but does suggest that only a small band migrated to these two areas, perhaps no larger than a few hundred.  The fact that they reached the Andaman islands may indicate that theirs was a boat-using culture.  Whatever, movement was rapid, possibly as high as 4 km per year, thereby allowing the early colonisation of Australia.

Analyses of mtDNA in Africa suggest that about 85 ka ago there was a major expansion of people, whose descendants make up more than two thirds of modern Africans.  Could it be that this expansion reflected climate and ecological change, so that migration from elsewhere drove inhabitants of the Red Sea coast to cross the daunting Straits of Bab el Mandab because of severe competition?  Perhaps it was the driving force as late as 40 ka, when modern humans reached Europe itself, undoubtedly along the Middle East route.

See also:  Forster, P. & Matsumura, S. 2005.  Did early humans go north or south?  Science, v. 3308, p. 965-966.

Because humanity and its activities have transformed the vegetated face of our home planet, caused its climate to warm and pushed an increasing number of other species over the edge of extinction, some circles have coined the name “Anthropocene” for the last half of the Holocene Epoch.  Human induced change almost certainly began as soon as settled agriculture arose to dominate most societies (see Did the earliest agriculture kick-start global warming?, in EPN of April 2005).  In terms of atmospheric emissions and mobilizing metals we now push natural rates close: facts that emerge from annual reviews of mining and energy use.  But are we truly significant geological agents as well as influences on the atmosphere and biosphere?  Two articles in April 2005 suggest that we are.

Quarries, mines and other excavations are obvious signs of human erosive power, but our farming activities produce insidious results by inducing soil erosion.  Although its effects are well known from such areas as the Ethiopian Highlands and the 1930’s “Dust Bowl” of the US mid-west, a global measure of the rates involved requires a careful compilation of  quantitative data.  Bruce Wilkinson of the University of Michigan has made the first attempt (Wilkinson, B.H. 2005.  Humans as geological agents: A deep-time perspective.  Geology, v. 33, p. 161-164).  Throughout the Phanerozoic, the volume of sedimentary rocks suggests that enough erosion has taken place to have stripped a uniform blanket 3 km deep from the continental surface.  That gives an average erosion rate for the last half-billion years of Earth history of the order of tens of metres per million years.  Assembling information about current rates of human-induced stripping, roughly divided 30:70 between excavation and soil erosion, Wilkinson arrives at a staggering figure for anthropogenic denudation: hundreds of metres per million years.  Our activities in the outer part of the rock cycle are an order of magnitude greater than purely natural rates of weathering, erosion and transportation.  He suggests that humanity began to outpace sedimentology sometime around the time of the Norman Conquest.

This awesome picture might seem to indicate that rates of sediment deposition on continental margins are also tremendously elevated by our actions.  That aspect has been studied by geoscientists from the US and Holland (Syvitski, J.P.M. 2005.  Impact of humans on the flux of terrestrial sediment to the global coastal ocean.  Science, v. 308, p. 376-380).  The opposite is now happening.  Syvitski et al.’s analysis of historical sediment loads in the catchments and lower reaches of the worlds major rivers shows that while overall sediment transport has increased by 2.3 billion t per year, since human effects became noticeable in the sedimentary record, the amount delivered to the sea has fallen.  Some 1.4 billion t no longer add to marine sedimentation each year.  Instead, that mass ends up behind dams of one kind or another.  In the last 50 years, more than 100 billion t, containing 1 to 3 billion t of carbon is in silted up reservoirs, or redistributed to farmland by irrigation diversions.  One of the outcomes is that natural coastal protection by spits and sand bars is growing less effective.  Another is that less nutrients are getting to the near-shore marine biosphere, with possible effects on fish stocks, coral reefs and other habitats.

Caring among the Erects

Dmanisi in Georgia provided one great surprise in human evolution by yielding abundant remains of 1.7 Ma old Homo erectus where they might be least expected: north of the Caucasus mountains that would have formed a tremendous barrier to any migration from further south.  The archaeological sites have provided another surprise in the form of a well-preserved skull of a completely toothless individual.  It is clear from the regrowth of bone into the sockets that this “masticatorily impaired” individual survived for years after losing all their teeth (Lordkipanidze, D. et al. 2005.  The earliest toothless hominin skull.  Nature, v. 434, p. 717-718).  It is impossible to believe that the individual could have survived on a tough meat and vegetable diet without special preparation of soft victuals.  Although the person’s survival cannot prove that other Erects helped out, that is a distinct possibility.  Losing teeth through dental disease or trauma would have been immensely painful and debilitating, yet the individual did survive.  We have to move forward to around 40 thousand years ago for compelling evidence that Neanderthal society cared for disadvantaged people, when several near-complete skeletons show evidence of long-term, crippling damage.

Most climate scientists encourage us to believe that planetary warming caused by gas emission from our energy intensive life style is both new and an inevitable context for our future.  Yet, one leading authority on past climates, William Ruddiman of the University of Virginia, reminds us that it isn’t only cars and power stations that release warming gases (Ruddiman, W.F. 2005.  How did humans first alter global climate. Scientific American, v. 292 March 2005, p. 34-41).  New evidence from air bubbles in the Vostok core through Antarctic ice shows a strange deviation of atmospheric CO₂ around 8000 years ago, from a downward trend in the early Holocene to one that relentlessly rises to the levels that characterised the recent pre-industrial world.  At around that time early agriculturalists in Europe and China began to chop down forest to make fields, thereby releasing the carbon content of felled trees to the atmosphere as CO₂.  By 5000 years before present, rice cultivation in East Asia had begun the release of methane from waterlogged paddy fields, and the methane content of ice bubbles reveals a reversal of methane decline at that time exactly..  Ruddiman’s view is that the release of both “greenhouse” gases reversed a natural cooling trend, and that growing populations sustained growth in atmospheric CO₂ (methane is quickly oxidised in the atmosphere). Comparing the rising CO₂ of the Holocene with its records in ice-bubble for the previous three interglacials, shows that in each previous case the gas rose to a maximum early in the interglacials and then declined steadily.  The invention of agriculture and its spread from around 11000 years ago in the Near East, he claims, could have staved off the onset of global cooling and the climatic descent into another glacial epoch, by eventually adding 40 parts per million of CO₂ to the air.  To support his hypothesis Ruiddiman compares the more recent ice-core records with historic catastrophes, mainly plagues that wiped out substantial proportions of the word population .  Sure enough, there are falls in CO₂ at the time of each major plague; that between 540 to 542 AD in Europe, the Black Death of the Middle Ages, and the reduction of the population of the Americas by maybe 90% when “Old World” diseases such as smallpox and measles met no resistance among native peoples.  In many respects Ruddiman’s ideas seem plausible, until we see the data.  The problem with ice core data is that its resolution degrades through time, and before 70000 years ago, no annual layers are preserved in glacial ice.  Moreover, records from different Antarctic cores differ wildly for the historic period and Ruddiman does not show the record from Greenland ice.  Finally, records of ice volume and ice-cap temperatures, derived from marine and glacial oxygen isotope records, show that each previous interglacial involved very different fluctuations in many other climate-related parameters.  If nothing else, Ruddiman’s  ideas will be challenged and the issue will “run and run” until the next “big thing”.

The tiny adult remains of Homo floresiensis reported in 2004 (see The little people of Flores, Indonesia, November 2004 issue of EPN) astonished the palaeoanthropological community more than any discovery since René Dubois’ found the first H. erectus remains on nearby Java almost a century ago.  Their recent geological age (about 13 ka), together with evidence for cohabiting the island of  Flores with fully modern humans and legends of the ebu gogo – “the grandmother who eats anything” spice up the find no end.  So it is not surprising that Scientific American has commissioned an excellent popularised account of where things stand with the little people only a few months after the discovery was announced in Nature (Wong, K. 2005.  The littlest human.  Scientific American February 2005 issue, p. 40-49).  It is not just the sheer tinyness of Homo floresiensis that draws our attention, but the fact that with a brain no larger than 2 Ma old australopithecines, the species crafted tools that are far more sophisticated than those of their most likely ancestor, H. erectus.  They also found their way across a seaway that could never have dried out during glacial maxima, used fire, and just as important survived competition with fully modern humans for around 20 ka.  Yet, as the article is at pains to point out, the find is so new that it is easy for specialists to kid themselves into believing a great deal more than may eventually turn out to be likely.  With two cultures on one small island, there may well have been mixing of artefacts, and also occupation of the site – a large cave – by both over the long period when they shared the island.  Opinion of many leading figures in the field is related by Kate Wong, and it is very clear that there is a lot of puzzlement.

The oldest modern humans

For a long time it has been known that the “front line” between fully modern humans and European Neanderthals was in the Middle East, with fluctuating occupation of highly productive sites since around 100 ka.  It is also well established that the ancestors of all of us outside Africa began to migrate some 70 to 80 thousand years ago, the signs being that the pressure was drying of the continent as global climate cooled.  The route take is not at all well defined, but one possibility is across the Straits of Bab el Mandab at the entrance to the Red Sea as islands became exposed when sea level began to fall.  So, fully modern humans originated in Africa, but where and when?  Unsurprisingly because of the intensity of research there since the discovery of Lucy, the Afar Depression of Ethiopia has provided most remains of H. sapiens sapiens.  Volcanic ash layers in sediments that contain specimens there give ages up to about 160 ka.  But Ethiopia has other hominid-rich sequences, including ones that have yielded anatomically modern humans.  The most notable is the Late Pleistocene Kibish Formation of the Omo River basin in southern Ethiopia, a deltaic sequence that formed when Lake Turkana had higher levels.  Human remains occur in the lower part of the Kibish Formation, and as luck would have it, they occur between two volcanic ash horizons and can be accurately dated (McDougall, I et al. 2005.  Stratigraphic placement and age of modern humans from Kibish, Ethiopia.  Nature, v. 433, p. 733-736).  For the moment, they are the oldest proper humans at 195 ka.  That age has interesting connotations as regards the climatic conditions of their lives.  The Omo basin shares watersheds with drainages into the Blue and White Nile system.  At 195 ka increased deposition of organic matter characterised the sediments beneath the Nile delta, which suggests greatly increased rainfall in the uppermost reaches of the Nile system.  That coincides with the onset of deposition of the Kibish Formation when Lake Turkana stood much higher than at present.  The area would have been lush.

A challenging question about the origin of fully modern humans is whether or not Homo sapiens interbred with archaic species, such as the Neanderthals or H. erectus.  That modern humans occupied the same territory as both, at the same time, is well established for Europe and Asia.  The likely time for the first major migration of moderns from Africa is about 70 to 100 thousand years ago, and archaic humans did not become extinct in Eurasia until 30 ka at the earliest.  Genetic material from extinct humans is rare and difficult to analyse because of degradation.  A couple of mtDNA samples from Neanderthal remains give results that are sufficiently different from ours to rule out retention in modern human populations of the genetic outcome of any interbreeding between ancestral moderns and the population to which the two Neanderthals belonged.  Yet it does not rule out such interactions with other archaic groups.  We have no idea of the genetic diversity of Neanderthals, whose lineage probably split from that of our own (through that of H. heidelburgensis) as long ago as 700 ka.  If they lived in isolated bands of a small population, that diversity could have become substantial over such a long time.    So far, no genetic material has been recovered from H. erectus remains.  Another approach to the matter has emerged from a genetic study of human head and body lice – Pediculus humanus (Reed DL. et al. 2004.  Genetic analysis of lice supports direct contact between modern and archaic humans. Public Library of Science Biology, v. 2, e340 – through www.plos.org). The louse Pediculus humanus is unique to humans, and genetic comparison with that which infests chimpanzees suggests that these two species diverged at about the same time as the split that led to modern humans and chimps, at about 5.6 Ma. That is remarkably similar to molecular timing that uses primate DNA.  The interesting feature of the louse genetic analyses by the team from the Universities of Florida, Utah and Glasgow is that there are differences between the lice that leap on us.  There are two strains which originated before 1 Ma ago, according to the molecular clock.  One has a global distribution, and infests both head and body, whereas the other is exclusively a head louse and only occurs in the Americas.

Around 1 Ma there seems also to have been a major divergence among early humans between a strand of H. erectus, which survived until as recently as 20 ka in Asia, and one that led to European Neanderthals and the modern humans who began to migrate from Africa to Eurasia around 100 ka.  The unique occurrence of the head-only louse in the Americas (along with the other strain) suggests that the modern humans who crossed the Bering Straits to colonise the Americas came into direct physical contact with beings who carried that particular strain, en route.  The likely candidates would have been Asian H. erectus.  Contact had to be direct, because, unlike the flea, the louse cannot leap, and it can only survive on humans.  The lack of the New World Pediculus humanus in Eurasia suggests two things: if moderns were “in touch” with archaics, the latter carried the other variant (Neanderthals?); the present Asian population (and that of New Guinea and Australia) possibly did not have close contact with archaics who were alive at the time of colonisation (were there by then very few?).  All very interesting, but it does not resolve the question of interbreeding; intimate contact could have been through fighting, trading or interbreeding.  There is another, very different human-only louse, Pthirus pubis, which infests pubic hair only, and about which there is very little genetic information, so far…

Jared Diamond is a behavioural scientist who specialises in birds of east Asia and the Pacific, but he has made a major contribution to the popularisation of anthropology through his books The Third Chimpanzee and Guns, Germs and Steel.  His vast knowledge of the west Pacific makes him an able commentator on the amazing find of tiny people on the island of Flores (see: The little people of Flores, Indonesia in November 2004 issue of EPN).  He writes of the sheer diversity of opportunities for colonisation of the archipelagos that separate New Guinea from mainland Asia by Homo erectus, who populated the Far East for around 1.8 Ma (Diamond, J.  2004.  The astonishing micropygmies.  Science, v. 306, p. 2047-2048).  There has been speculation that Homo floresiensis became so small in response to a limited biological productivity on Flores, but Diamond is not at all sure – the Indonesian island chain has luxuriant flora and fauna compared with the Asian mainland.  But islands have limits to any population. Homo floresiensis probably arrived as a tiny group that flourished because of negligible competition.  Soon reaching the limits of support by the island ecosystem, full-sized colonisers with a limited gene pool would either die out or quickly generate smaller offspring, larger numbers of which could be sustained and reproduce.  Another of Diamond’s insights concerns the matter of similar populations on the many equally attractive islands in the chain.  If there were, that would imply easy island hopping, and therefore no reason for miniaturisation through evolution.  Modern humans have done just that, on the scale of the entire Pacific basin over the last 45 thousand years with no sign of evolving as dwarfed island populations – they had boats. Homo floresiensis’ ancestors almost certainly did not.  They could have swum the short distances between the islands at times of low sea-level, indeed they could have seen one island in the chain from the next.  In the case of New Guinea, had they reached the nearest island to it in modern Indonesia, they could never have seen it in the distance.  Diamond’s greatest surprise is how the micropygmies survived later fully human colonisation from 50 to 18 thousand years, when large people would have colonised the entire chain with ease, before proceeding to Australasia and Oceania.  Perhaps they coexisted through having a complementary food economy, as do modern African and Philippino pygmies, by some form of trade.  They may even have been too dangerous to hunt or attack.  Intellectually attractive as Homo floresiensis might be to us, steeped in Tolkienesque lore, Diamond cuts out the fantasy – they were so unhuman as to make the possibility of their disappearance through interbreeding highly unlikely.  Like chimpanzees, they would not only have been unappealing but possibly too unpredictable and strong for cross-species sex to have crossed the minds of fully human colonisers.

One of the great paradoxes in palaeoanthropology is how modern humans in Europe survived the last glacial maximum whereas Neanderthals did not.  In fact they became extinct some 10 thousand years before conditions reached their coldest.  The paradox lies in the fact that Neanderthals were superbly adapted physiologically and behaviourally to life in cold, harsh conditions, having lived through the previous glacial period since at least 200 ka ago.  Modern humans evolved, since first appearing around 160 ka, by adapting to conditions in Africa – an environment far different from that of Europe in every conceivable way – and bands migrated outwards, probably because of growing aridity as global climate cooled.  Their future was akin to that of Africans from modern Kenya, should they decide to migrate to Arctic Canada.  Quite probably Kenyans would survive, because the Innuit are supremely generous and friendly people.  They have to be in order to have survived their chosen environment.  It is this paradox that concerns archaeologist Paul Mellars of Cambridge University (Mellars, P. 2004.  Neanderthals and the modern human colonization of Europe.  Nature, v. 432, p. 461-465).  Genetic evidence from recovered Neanderthal DNA shows conclusively that the two occupying groups in Europe did not interbreed to any significant extent, so the paradox can therefore not be resolved by complete hybridisation.  To what extent were modern humans better equipped with tools than were Neanderthals?  The archaeological record shows that from about 40 to 35 ka there was a burst of cultural advance among moderns, that spanned the Middle East to the Atlantic shores of Spain – the Aurignacian technology.  It coincided with an equally explosive spread of aesthetic culture, involving such symbolism as to be widely considered as a mark of sophisticated language and communication, perhaps a sign of an advance in brain structure that Neanderthals did not experience.  One of the big surprises in recent archaeology of this crucial period was that modern human remains associated with early Aurignacian artefacts turned out to be burials later than the tools were discarded.  To some, this left open the possibility that the technological advance may have been achieved by earlier occupants – the Neanderthals themselves.  Indeed there are signs that these original Europeans did make cultural advances around that time, in the form of the Chatelperronian artefacts.  Mellars points out that moderns of the time did not bury their dead near habitations, whereas Neanderthals made a habit of it, so the inference of especially smart Neanderthals is probably unfounded.  There are two geographic patterns associated with the Aurignacian, one arcing through Central Europe to France, the other along the Mediterranean coast, each showing distinct differences in technology.  This is regarded as support for two populations of colonising moderns.  The Chatelperronian is now regarded as one of many signs of some kind of cultural transfer between Neanderthals and moderns, and therefore of regular contact.  Whatever those contacts involved is unknown, but immaterial as regards the fate of the Neanderthals.  They disappeared without a trace, by 30 ka at the latest.  Mellars’ review concludes with the view that this extinction was a matter of outcompetition, as conditions were steadily deteriorating towards the last glacial maximum.  It could well be that moderns, faced by the perils of a move to harsher conditions that were oscillating rapidly due to Dansgaard-Oeschger events, were forced to adapt or perish.  The Neanderthals did not, or they did it too late.  Their culture had served them well, and why should they have changed it?

A discovery that will run and run?

Do you know why humans have prominent buttocks (the ape has none worth a sidelong glance)?  I thought not; most people do not wish to know.  Here is how to find out.  Begin to walk, preferably in secluded woodland.  Now clutch each “cheek”, one in either hand.  Do you notice anything?  No, the gluteus muscles do nothing, apart from wobble a bit.  Now, if this is possible, begin to lope along the path, still with a buttock in each hand.  There, they work!  Hominids are not just striding bipedalists, but evolved to run: not so fast as to collapse after a hundred metres, but kilometre after kilometre at a relentless lope.  This is the conclusion from anatomical and bio-mechanical study of hominid remains, going back to our oldest undisputed ancestors (Bramble, D.M. & Lieberman, D.E. 2004.  Endurance running and the evolution of Homo.  Nature, v.  432, p. 345-352).  The outcome is that modern humans, and probably every earlier species of Homo, can and did run any other animal to exhaustion.  The australopithecines probably could run down a hedgehog, but not prime meat.  The study goes further, since there is more to running than leaning forward and putting a leg out to stop us falling on our faces.  The arms are involved, and flexure of the waist.  Mechanically, a higher waist and shorter arms are more effective aids to running, as of course are proportionately long legs.  The technical arguments in this hypothesis are somewhat unfamiliar, except to the sports scientist, but one immediate conclusion is easy.  No modern hunter-gatherer really likes to run a marathon each day, even though they could, and would much rather sit and watch the world go by, so long as he or she is fed.  Unless the utter pointlessness of prolonged physical activity, other than a means of sustenance, becomes a cultural necessity for other reasons, the next stage in human evolution may well see the buttocks atrophy.  Legs will shorten, the waist drop and the arms lengthen, once more, to help us knuckle-walk up to the chip shop.  There may only be one way to preserve the buttocks; to encourage wolf packs in city parks.

Something to chew over

Much of the human evolutionary story depends on the most enduring of fossil material – teeth.  So, dentists have been drawn increasingly in palaeoanthropology.  Since species are defined as whole organisms, the use of such tiny fragments as teeth should be worrying.  But they are often the only material, and specialists in dentition have convinced themselves that teeth “work” as phylogenetic indicators.  But there are always dental variations between individuals, and therefore a danger of doing something akin to cheating with a jigsaw puzzle; forcing misfits into the cussed blue sky part in order to get on.  Recent research on the genetics that underlie the development of mouse teeth (Kangas, A.T. et al. 2004.  Nonindependence of mammalian dental characters.  Nature, v. 432, p. 211-214) shows that different levels of a protein (ectodysplasin) affect the shape changes during development of dentition..  Ordinary mice have different molars, depending on tiny differences in the growth points of tooth crowns during dental development, and that depends on ectodysplasin levels.  Clearly, major differences among fossil teeth ought to point to adaptation (and speciation) to very different diets and ways of biting.  But now there is a devil in the detail of the teeth of mammals, although the authors do not extend their observations explicitly to those of hominins. Specialists in human speciation will probably rationalise away the possibility of something going awry with the hominin clade, and perhaps rightly so, if the implications of Kangas and colleagues work diffuse to their arena.  However, everyone is aware of the dramatic polymorphism of human mastication, from mouth-filling “tombstones” to a tiny pointiness that worries the experienced observer.