Category: Anthropology and Geoarchaeology

The discovery from the Neanderthal genome that people outside Africa have such a muscular bloke in their distant ancestry (see Yes, it seems that they did…in May 2010 issue of EPN) ought to be quite enough of a shock for one year, but hard on its heels comes another. Animal bones from Ethiopia in sediments dated at more than 3.4 Ma show clear signs of having flesh cut from them with a sharp blade (McPherron, S.P. et al. 2010. Evidence for stone-tool assisted consumption of animal tissues before 3.39 million years ago at Dikika, Ethiopia. Nature, v. 466, p. 857-860). The oldest known stone tools date back only 2.4 Ma (none were found at Dikika), and those associated with a known hominin (H. habilis) to half a million years later than that. No species of the genus Homo is known to have been living 3.4 Ma ago, so a likely candidate for making and wielding stone tools then would be Australopithecus afarensis: Lucy’s genus. In fact the infant A. afarensis named Selam (see ‘Peace’ (Selam) disturbed in October 2006 issue of EPN) was found a mere 300 m away from the cut-marked bones.

There are several problems that arise from these butchered bones, as regards their implications. Do hominin specialists reserve the genus Homo exclusively for tool makers? If so, do Lucy and Selam become H. afarensis? But without actual tools associated with the bones, it is impossible to decide whether they were specifically made to deflesh prey or carrion, or were just sharp, naturally occurring bits of stone that some creature with insubstantial teeth happened to use to snaffle a quick snack from competing carnivores. Even more intriguing, in the light of the immense rarity of hominin remains, was there some creature more advanced than A. afarensis roaming the stifling plains of Ethiopia’s Awash valley 1.4 Ma before the first known tool maker? The various Awash projects will run and run after this new and startling discovery.

The discovery from the Neanderthal genome that people outside Africa have such a muscular bloke in their distant ancestry (see Yes, it seems that they did…in May 2010 issue of EPN) ought to be quite enough of a shock for one year, but hard on its heels comes another. Animal bones from Ethiopia in sediments dated at more than 3.4 Ma show clear signs of having flesh cut from them with a sharp blade (McPherron, S.P. et al. 2010. Evidence for stone-tool assisted consumption of animal tissues before 3.39 million years ago at Dikika, Ethiopia. Nature, v. 466, p. 857-860). The oldest known stone tools date back only 2.4 Ma (none were found at Dikika), and those associated with a known hominin (H. habilis) to half a million years later than that. No species of the genus Homo is known to have been living 3.4 Ma ago, so a likely candidate for making and wielding stone tools then would be Australopithecus afarensis: Lucy’s genus. In fact the infant A. afarensis named Selam (see ‘Peace’ (Selam) disturbed in October 2006 issue of EPN) was found a mere 300 m away from the cut-marked bones.

There are several problems that arise from these butchered bones, as regards their implications. Do hominin specialists reserve the genus Homo exclusively for tool makers? If so, do Lucy and Selam become H. afarensis? But without actual tools associated with the bones, it is impossible to decide whether they were specifically made to deflesh prey or carrion, or were just sharp, naturally occurring bits of stone that some creature with insubstantial teeth happened to use to snaffle a quick snack from competing carnivores. Even more intriguing, in the light of the immense rarity of hominin remains, was there some creature more advanced than A. afarensis roaming the stifling plains of Ethiopia’s Awash valley 1.4 Ma before the first known tool maker? The various Awash projects will run and run after this new and startling discovery.

Survival by the seaside

Increasingly, hominins have survived swings of climate by their wits and by chance. Neither underpin the instinct to migrate when times are hard, but where one ends up depended, until the Holocene, more on chance than design. Early migrations must have been more by diffusion than purposeful, especially in the vastness of the African continent. Yet groups of hominins found their way into Eurasia several times and thrived there. Far more of them would have met the coast far from a continental exit route, such as the Levant or the Straits of Bab el Mandab. However, in stressful glacial episodes reaching the coast was a key to survival as its food resources are almost limitless (see Human migration and sea food May 2000 issue of EPN). Our own species found refuge by the sea not long after we originated (Marean, C.W. 2010. When the sea saved humanity. Scientific American, v. 303 (August 2010), p. 40-47). Around 195 ka climate began to cool and dry to reach a glacial maximum at roughly 123 ka. Curtis Marean (Arizona State University, USA) was one of the first scientists to look for signs of coastal refuges in Africa during the early 1990s, particularly at its southern tip. With co-workers he found several caves on the coast of South Africa that yielded the evidence on which he has based a review of littoral survival opportunities and the skills that we developed. This particular coastal stretch has a huge diversity of plant life, most unique to it, and many of which store carbohydrate in tubers, bulbs and corms. They are adapted to dry conditions and need only the simplest technology – digging sticks and fires for cooking – to exploit starchy, easily digested energy resources, along with the more obvious animal protein sources present on all shorelines. Marean’s review puts in plain language all the discoveries made by his group over the last 20 years, including evidence of the use of fire treatment to improve flaked stone tools and the development of art based on iron-oxide pigments, plus his own take on their anthropological significance.

Earlier colonisers of northern Europe

The Pleistocene of East Anglia in England is a rich source of the high-latitude flora and fauna from early interglacials of the 1 Ma long series of 100 ka climate cycles. Eyed by archaeologists for decades as a potential source of human remains, a coastal site at Pakefield in Suffolk finally yielded stone tools in 2005 (see Earliest tourism in northern Europe in EPN January 2006). The enclosing sediments, to widespread excitement, turned out to be around 700 ka old, establishing the earliest known human colonisation at that latitude (52ºN). At that time East Anglia was connected to Europe during both glacial and interglacial periods, and was crossed by a now-vanished river system draining the Midlands and Wales into the proto-North Sea. Stone artifacts have now emerged from similar interglacial terrestrial sediments on the shore below the village of Happisburgh (pronounced ‘Haze-burra’) further north still, in Norfolk (Parfitt, S.A and 115 others 2010. Early Pleistocene human occupation at the edge of the boreal zone in northwest Europe. Nature, v. 466, p. 229-233). Magnetostratigraphy pushes back the human influence here to more than 800 ka, maybe as far back as 950 ka. As yet no human remains have been turned up, and the site is below high-tide level and liable to be destroyed by winter storms so work proceeds as fast as possible. Yet cliff erosion will inevitably reveal new material each spring.

Fauna and flora from Happisburgh indicate a slow flowing river flanked by coniferous forest with grassed clearings. Beetle fossils suggest summer temperatures slightly warmer than those in modern southern Britain, but with winters some 3ºC colder than now. The climate was analogous to that in southern Norway today, at the transition from temperate to boreal vegetation zones; certainly tough in winter for people without shelter. Yet the permanent connection with continental Europe would have permitted easy seasonal migration across great plains that extended to warmer southern climes. The tool-using people were not the earliest Europeans, for several archaeological sites in Spain, southern France and Italy extend back to 1.3 Ma. Who or rather what hominin species they were needs bones, preferably those of the head. The discovery that there were at least 4 hominin species cohabiting Eurasia during the last glacial epoch encourages caution in any speculation.

See also: Roberts, A.P. & Grűn, R. 2010. Early human northerners. Nature, v. 466, p. 189-190.

Now that the Neanderthal genome has revealed that non-Africans have a bit of the old chap inside us (see Yes, it seems that they did… in EPN May 2010), why not seek your inner Neanderthal? The famous Smithsonian Institution in Washington DC has released an application for iPhones, its first ever venture into ‘apps’, that allows users to morph their faces to resemble how they might have looked as a male or female H. neanderthalensis, H. heidelbergensis or even tiny H . floresiensis. The ‘app’ is called Meanderthal, which is especially apt as that neologism is street slang for a sad individual who roams supermarket aisles with a mobile phone welded to his or her ear.

Male relative of ‘Lucy’
Many people know of the amazing skeleton of a possible ancestor to humans discovered in NE Ethiopia by Donald Johanson in the late 1970s, and they know why it was dubbed ‘Lucy’. That type specimen of a female Australopithecus afarensis still figures in the media, but little appears concerning males of the species. That is not surprising for they are represented by only fragmentary and ambiguous remains. So a report on a 40% complete fossil male A. afarensis that includes limb and pelvic bones, and those of the neck, shoulder and arm is sure to cause a stir (Haile-Selassie, W. and 8 others 2010. An early Australopithecus afarensis postcranium from Woranso-Mille, Ethiopia. Proceedings of the National Academy of Science USA, v. 107, p. 12121–12126. doi/10.1073/pnas.1004527107). For starters, he is very big indeed compared with ‘Lucy’, standing between 1.5 and 1.7 m tall, and fragments of other individuals suggest that some males were larger still and within the modern human range. The conclusion must be that A. afarensis was sexually dimorphic: big males and diminutive females, which is the norm for chimps, orang utans and gorillas. Legs longer than arms suggest an upright walking posture, but the shoulder assembly is more gorilla-like than human. Yet ribs that indicate a barrel chest show a more human form than would other great apes. The authors suggest that the lack of consistent resemblance to any one of the living hominids may indicate that the last common ancestor that we share with the others may not have closely resembled any of the living forms. The big problem with the find is its antiquity: at 3.6 Ma it is a lot older than ‘Lucy’. Without teeth or at least part of a skull, assigning it to the same species carries no certainty.

Led by João Zilhão of the University of Bristol, UK, a team of British, French, Italian and Spanish archaeologists and anthropologists have at a stroke rid our former companions in Europe, the Neanderthals, of the popular and academic stigma of being uncultured (Zilhao, J. and 16 others 2010. Symbolic use of marine shells and mineral pigments by Iberian Neandertals. Proceedings of the National Academy of Sciences, v. 107 p. 1023-1028). They wore jewellery in the form of necklaces and pendants of bivalve shells, remains of which have turned up in large numbers in caves and rock shelters in the interior of southeast Spain. Some of the perforated shells show clear signs of having been painted, and a few show grooves worn by string. They found even a paint container and painting tools made of small bones from a horse’s foot. The container and tools retain distinct traces of pigment made from the common iron colorants goethite, jarosite and hematite. One large, perforated scallop shell shows that its white interior was painted to match its reddish exterior.

It has often been commented that Neanderthal adornments ( a few possible finds precede this work) and intricate tools were simply copied from those of fully modern humans. The deposits containing this ornamentation are around 50 thousand years old: preceding modern human occupation of the Iberian Peninsula by at least 10 ka. Evidence for artistic work by early H. sapiens comes from South Africa as far back as 165 ka (see Technology, culture and migration in the Middle Palaeolithic of southern Africa in January 2009 EPN, and When and where ‘culture’ began in EPN of November 2007). Iron-based pigments are still widely used for body painting in many societies, but obviously that use will not feature directly in archaeological finds. Association of lumps of potential pigments with hominin tools go back even further in Africa, beyond the presence of fully modern humans, but to ascribe pieces of say hematite to cultural practice needs evidence for scraping or grinding. There seems no reason why Neanderthals and modern humans maintained an ancient cultural tradition.

Perhaps now the myth of brutish Neanderthals will finally be laid to rest. Thanks to the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, we have a nuclear genome of H. neanderthalensis; in fact a composite based on bones of three individuals from a Croatian cave. Carbon-14 dating shows that the bones are between  44 to 38 ka old: about the time of the first arrival of fully modern humans in Europe. Only ten years on from the publication of the first human genome, the team inspired by Svante Paabo (actually the last of 56 authors, but the founder of the lab and its peerless facilities) has engineered a scientific triumph that matches the achievement in 2000 led by James D. Watson at the U.S. National Institutes of Health and Craig Ventner of Celera Corporation (Green, R.E. and 55 others 2010. A draft sequence of the Neandertal genome. Science, v.  328, p. 710-722). Let’s be frank, to get to know another member of our genus nearly as well as ourselves, albeit in terms of A, C, T and G the nucleotide bases of DNA adenine, cytosine, thymine and guanine, puts the rest of science in somewhat distant perspective. It forms the basis for learning what, if anything, sets us apart from earlier humans, what we share with them and potentially how we came to be what we are.

Apart from a geologically brief period since 80 ka when fully modern humans and Neanderthals occupied the Mediterranean fringe of the Middle East, both had probably developed separately since forebears of the Neanderthals left Africa to arrive in Europe about 400 ka ago while ours seem to have stayed in Africa. Earlier genetic results show that both species shared a common ancestor, perhaps H. heidelburgensis. From the time when the main wave of African people ventured into Arabia, Asia and Europe, perhaps around 60 to 75 ka, chances are that encounters were inevitable, until the last Neanderthals met a lonely end on the Rock of Gibraltar around 25 ka. Variations in mtDNA data seem to show that the two species have little genetic overlap, but mitochondria hold only a small part of DNA. The 4 billion base pairs of nuclear DNA occur in thousands of segments that have evolved independently, and in us continue to do so: a source for very detailed comparisons indeed. The issue centres on how alike and how different such segments are, when compared with DNA from different modern human genomes. If similarities and contrasts are more or less the same in comparison with all modern human groups, then it is most likely that although Neanderthals and modern humans did meet they did not exchange genetic materials; i.e. they did not mate successfully. The new data show beyond much doubt that Neanderthals were more similar genetically to modern Europeans and Asians than they were to modern Africans. There was successful mating and the progeny entered the fully modern human population of Asia and Europe, to the extent that Asians and Europeans host 1 to 4% of Neanderthal ancestry.

The most famous human in genetics, simply because he arranged sequencing of his own DNA, which is the comparator used by the team, Craig Ventner can be highly confident that he contains segments of Neanderthal DNA. We must await his reaction in a mood of solemn gaiety, and react he most probably will: I did and I feel quite cheerfully proud. Interestingly, Neanderthals are as closely related to individuals from New Guinea and China as they are to a French person. Such uniformity among non-Africans suggests that the gene exchange (viz. sexual intercourse) took place shortly after fully modern humans migrated out of Africa. But who did what to whom under which circumstances will remain a mystery, although it appears that the gene flow was from Neanderthal to human and not vice versa. With a small colonising group of Africans, there need not have been a great deal of ‘sharing’ of bodily fluids for introduced genes to ‘surf’ throughout succeeding generations to reach us. So what is it that we lucky ones share with Neanderthals? This is a topic fraught with possible overtones, though they probably will not suit the outlook of those with a prejudiced racist tendency. The results suggest 15 genomic regions that include those involved in energy metabolism, possibly associated with type 2 diabetes; cranial shape and cognitive abilities, perhaps linked to Down’s syndrome, autism and schizophrenia; wound healing; skin, sweat glands, hair follicles and skin pigmentation; and barrel chests. Some may have been beneficial others not, but they have been retained through thousands of fully modern human generations.

Analyses of the genome are at a very early stage, but the sequencing technique and associated checks for contamination with modern DNA are sufficiently advanced that other Neanderthal remains and bones of ancient Europeans and Asians will surely add to the excitement. Just how far back analyses can be pushed remains to be seen, but it is now quite clear that human evolution was a great deal more complicated than the simple Out-of-Africa model that is currently almost universally accepted.

See also: Gibbons, A. 2010. Close encounters of the prehistoric kind. Science, p. 680-684.

Other rich hominin pickings

March and April 2010 were indeed exciting times for palaeoanthropology, with publication of evidence for two new species of hominin. Cave systems in the Archaean limestones of north-eastern South Africa have yielded so many fossil remains related to human evolution that the area liberally dotted with them has UN World Heritage status. The caves formed beneath a now-eroded plateau, and are so rich because creatures fell into surface sink holes, died and remained little disturbed by scavengers. The latest find has an unusual story behind it (Balter, M. 2010. Candidate human ancestor from South Africa sparks praise and debate. Science. v. 328, p. 154-155). The cave system was first explored by lime-kiln workers around the early 1900s, who brought out blocks which litter the ground around cave mouths. It was in one of these chunks that the 9-year old son of a South African palaeoanthropologist found bone that turned out to be a hominin lower jaw. Sadly, young Matthew Berger had to be excluded from the list of authors of the two important papers that ensued from his find, because of Science magazine’s rules for authorship (Berger, L.R. et al. 2010. Australopithecus sediba: a new species of Homo­-like australopith from South Africa. Science, v. 328, p.195-204. Dirks, P.H.G.M. and 11 others 2010. Geological setting and age of Australopithecus sediba from southern Africa. Science, v. 328, p.205-208). Nevertheless, he can be well satisfied as the full set of bones points to a new species, one that may arguably share more features with Homo species of about the same antiquity than any other australopithecine. Being coeval with H habilis, A. sediba cannot be ancestral but may have shared a common ancestor with the earliest known human species. Fitting the new find into the long and variously disputed cladistics of hominins will run and run, but at least it should re-emphasise one thing: there were several cohabiting hominin species in Africa around 2 Ma ago.

Such a multiplicity of co-existing hominins seemingly continued until quite recent times, as a remarkable piece of evidence from a Siberian cave has confirmed. Between about 30 to 48 ka, the cave was a popular venue for Neanderthal hunters who left tools and bones of their prey. Russian archaeologists combed the cave deposits for human remains but came up with only fragmentary finds of bone. One of these was the tip of someone’s little finger. The possibility of obtaining genetic material from relatively young finds in caves that have remained cold and untouched encouraged the excavators to handle their finds carefully. It’s just as well they did for the results from the Max Planck Institute for Evolutionary Anthropology in Leipzig Germany, famous for its work on Neanderthal DNA, held a surprise. The finger’s owner was neither a Neanderthal nor a fully modern human (Krause, J. et al. 2010. The complete mitochondrial DNA genome of an unknown hominin from Southern Siberia. Nature, v. 464, p. 894-897). The evidence for this is overwhelming. Fully modern human mtDNA ranges from 0 to about 100 differences in nucleotide positions, the difference between human and Nenaderthal mtDNA is just over 200, but the pinky bone revealed almost 400 differences from ourselves and almost as many from Neanderthals. Such differences suggest that ancestors of the unknown Siberian separated from the line of descent to Neanderthals and modern humans about a million years ago. Yet all three were in Asia a mere 40 ka ago. Add to that the diminutive H. floresiensis who survived to cohabit Flores with modern humans until about 9ka, and some evidence that H. erectus was also around in Java up to 25 ka, gives possibly 5 species of human in Asia who may have met and goodness knows what else.

See also: Dalton, R. 2010. Fossil finger points to new human species. Nature, v. 464, p. 472-473.

Led by João Zilhão of the University of Bristol, UK, a team of British, French, Italian and Spanish archaeologists and anthropologists have at a stroke rid our former companions in Europe, the Neanderthals, of the popular and academic stigma of being uncultured (Zilhao, J. and 16 others 2010. Symbolic use of marine shells and mineral pigments by Iberian Neandertals. Proceedings of the National Academy of Sciences, v. 107 p. 1023-1028). They wore jewellery in the form of necklaces and pendants of bivalve shells, remains of which have turned up in large numbers in caves and rock shelters in the interior of southeast Spain. Some of the perforated shells show clear signs of having been painted, and a few show grooves worn by string. They found even a paint container and painting tools made of small bones from a horse’s foot. The container and tools retain distinct traces of pigment made from the common iron colorants goethite, jarosite and hematite. One large, perforated scallop shell shows that its white interior was painted to match its reddish exterior.

It has often been commented that Neanderthal adornments ( a few possible finds precede this work) and intricate tools were simply copied from those of fully modern humans. The deposits containing this ornamentation are around 50 thousand years old: preceding modern human occupation of the Iberian Peninsula by at least 10 ka. Evidence for artistic work by early H. sapiens comes from South Africa as far back as 165 ka (see Technology, culture and migration in the Middle Palaeolithic of southern Africa in January 2009 EPN, and When and where ‘culture’ began in EPN of November 2007). Iron-based pigments are still widely used for body painting in many societies, but obviously that use will not feature directly in archaeological finds. Association of lumps of potential pigments with hominin tools go back even further in Africa, beyond the presence of fully modern humans, but to ascribe pieces of say hematite to cultural practice needs evidence for scraping or grinding. There seems no reason why Neanderthals and modern humans maintained an ancient cultural tradition.

A fragile consensus has developed concerning the date when fully modern humans left Africa then migrated to all habitable continents. It is based on genetic comparisons among living people, very sparse occurrences of H. sapiens remains that have been dated and on the environmental pressures in Africa to migrate during the highly erratic deterioration of climate since the last interglacial. The last included a series of abrupt cooling and drying episodes around 118, 110, 86, 75, 71 and 67 ka. That fully modern humans entered the Middle East from time to time between 130 and 75 ka is backed up by actual fossils, but most palaeoanthropologists believe that they moved no further, because of the growth of surrounding deserts, and probably did not return until around 45 ka. The consensus for the decisive move out of Africa to Eurasia is that it was via the Straits of Bab el Mandab at the entrance to the Red Sea, when sea level fell to a level that would have allowed a crossing by rafting over narrow seaways. The most likely was during the brief 67 ka cool/dry episode that coincided with an 80 m fall in global sea level: the largest since the previous glacial maximum. This would fit the earliest dates of fully modern human remains in Asia and Australasia. There had been falls of more than 50 m around 110, 86 and 75 ka, each followed by rising sea level. Each of them accompanied by cooling and drying in Africa conceivably could have allowed earlier migrations from Africa to southern Arabia. Emerging data seems set to complicate matters.

At a conference in Gibraltar during September 2009 (Balter, M. 2009. New work may complicate history of Neandertals and H. sapiens. Science, v. 326, p. 224-225) there were further reports of stone tools, which apparently resemble those of a similar age from Africa, beneath the 74 ka Toba ash in South India, and dated between 70 to 80 ka old in the Yemen and United Arab Emirates. Even more challenging are reports of archaic H. sapiens teeth and a jawbone with a chin – a sure sign of a fully modern human – from cave sediments in southern China that yield a date of about 110 ka (Stone, R. 2009. Signs of early Homo sapiens in China. Science, v. 326, p. 655). Given an opportunity and a need humans do tend to move in order to survive, a proclivity that would undoubtedly be boosted by our insatiable curiosity: after all H. erectus, antecessor and neanderthalensis all made tremendous migrations starting more than 1.6 Ma ago.

 

Fungal clue to fate of North American megafauna

More than 30 large mammal species, including elephants and giant sloths, that had roamed North America during the Pleistocene met their end between 13 and 11.5 ka. Whether or not predation by newly arrived humans caused these extinctions remains unresolved, as do the triggers for coinciding changes in plant communities and evidence for increased burning of biomass. While the ages of fossil bones are direct evidence for species being present, they are not found everywhere that a megafauna likely lived and occurrences are patchy in time. There is however a proxy for the presence or absence of large herbivores: spores of fungus that thrived on their dung (Gill, J.L. et al. 2009. Pleistocene megafaunal collapse, novel plant communities, and enhanced fire regimes in North America. Science, v. 326, p. 1100-1103). Sporormiella can only complete its life cycle after herbivores have digested plant matter. So its spores in sediment cores form an impressive link to the local presence of herds. In a lake core from New York State such fungal spores, having been much more abundant beforehand, fell to less than 2% of all spores and pollen about 13.7 thousand years ago. This suggests that large herbivores vanished from this area at that time. Interestingly, the timing is during a warm period (the Bølling-Allerød) rather than the stress of the Younger Dryas glacial re-advance. Moreover, the local disappearance predates the first signs of Clovis people, although there is evidence for earlier human colonisers back to 15 ka. It is possible that it was the disappearance of large herbivores that allowed the development of extensive mixed coniferous-deciduous woodland, broad-leaved trees having perhaps been browsed severely by earlier herbivores.

I first mentioned Ardipithecus ramidus in EPN for February 2002 (Taking stock of hominid evolution), and the remarkable first finds by Tim White and his team were in 1994. Fifteen years on, and having amassed fragments of at least 36 individuals (and thousands of vertebrate, invertebrate and plant fossils) – Owen Lovejoy of Kent State University remarked, ‘This team seems to suck fossils out of the ground’ – it’s pay day! A total of 54 pages of the 2 October 2009 issue of Science (v. 326, Issue 5949) are devoted to this diminutive and very old (4.4 Ma) hominin. Such mounds of data wrested from the cauldron of the Afar Depression needed a long incubation period, and what is presented in Science is a summary rather than being comprehensive: much more is available online, and yet to come. The now hugely experienced, 47-strong academic team built up by Tim White and his original colleagues deserve massive congratulations. But they depended on the eagle-eyed, mainly Ethiopian fossil finders, many of whom are Afar pastoralists who took to field palaeontology as ducks to water. Science in general owes a massive debt to all those who have wrested such a wealth of anatomical information from every aspect of the fossils and their environmental context. What they have achieved is more worthy of Nobel-status than the fumbling of gaggles of annual economist-laureates who still cannot grasp why the world economy continually does grave disservice to humanity. The Ar. ramidus team also have a lot more worth saying to us than those physicists who seek the grail of a theory of everything – racked by such hubris that they are both unintelligible and unrealistic in the most literal way.

I cannot do adequate justice to the work in that historic issue of Science, but there are some general points that will leave any interested person breathless. As regards previous assumptions about the environment under which hominins emerged, it was woodland not open savannah. Though upright and capable of walking, as revealed by pelvis remains, Ardipithecus had feet with opposable big toes: sort of foot-thumbs. So they would have been as comfortable on trees as on the ground. Yet, their foot-architecture shows signs of having evolved from  monkey-like feet rather than any lin=ke those of modern gorillas and chimps. A degree of certainty accompanies anatomical discussions, for one individual female Ar. ramidus is represented by a large proportion of a full skeleton, rivalling the later remains of  ‘Lucy’, an Australopithecus afarensis. Her skull, reconstructed from a badly crushed state using co0mputed tomography and digital piecing-together, gives a brain size around the same as bonobo chimpanzees, and less than that of australopithecines. The feet clearly show a walker able to clamber, rather than swing and knuckle walk. Hands, though primitive, are more human-like than those of living apes are. From that can be concluded that a common ancestor a million of so years earlier was not ape-like in manual terms: chimps have evolved in this respect perhaps a lot more than those on the human line. Teeth shape, wear and isotopic signatures suggest a broad diet, rather than specialisation, from which grasses and grass-eating prey seem absent. Moreover, there is no sign of large canines, that could indicate minimal social aggression. Males and females were of similar size, as are we, rather than showing the sexual dimorphism that characterised later australopithecines and both chimps and gorillas. This also seems to point backwards in time to the last common ancestor of ourselves and chimps being very different from both living genera. Yet in many respects chimps seem to have evolved more than hominins. Because of the work on Ar. Ramidus, a chimpanzee-centric view of our shared forebears and therefore of hominin evolution can now be rejected. Perhaps thankfully, speculation about aspects of our behaviour stemming from those of chimpanzees is probably worthless.

The mass of data concerning this small, Pliocene hominin holds out a promise of yet more to come, both further back in time, and to populate the gaps in time and morphology that currently plague palaeoanthropology. The terrestrial sediments in which White et al. found Ar. Ramidus are 300 m thick, cover 5.5 to 3.8 Ma and are exposed over a large area. The stratum from which most data were recovered represents at most about 10 thousand years. Elsewhere in the Afar-Danakil Depression are other sediments laid down in river and lake systems that go back as far the Miocene (the estimated time of the last common ancestor of other primates and humans), and are still being deposited today. If anything characterised this triumph of the human intellect, it combined patience, determination and an attention to detail that was shared by every participant.

Native people in Australia have been spoiled for choice of materials from which to make superb stone tools, all kinds of silica rock being available in the bedrock and the widespread tropical soils, including multicoloured chalcedony and even opal. Their master craftsmen developed a form of heat treatment that subtly modifies silica’s internal structure so that gentle application of pressure to the edges of lumps removes small flakes to give intricate sharp edges, including barbs for fishing spears. This pyrotechnology leaves easily recognised signs in stone tools: colour changes and a pearly lustre.

A large team of archaeologists and geoscientists from South Africa, Australia, the UK and France have sifted through tools collected from the 35 to 280 ka African Middle Stone Age (defined differently from the European Mesolithic) in search of evidence for fire treatment (Brown, K.S. and 8 others 2009. Fire as an engineering tool of early modern humans. Science, v. 325, p. 859-862). Like signs of symbolic behaviour (see Technology, culture and migration in the Middle Palaeolithic of southern Africa and Deeper roots of culture in January and March 2009 issues of EPN) fire-worked silica tools appear as early as 164 ka ago. However, this is the first paper that reports a search for such technology, and since fire was definitely used by even earlier humans, such as Homo antecessor around 790 ka (see Early, microscopic evidence for human control of fire in November 2008 issue of EPN) expect earlier finds to be announced.

See also: Webb, J. and Domansski, M. 2009. Fire and stone. Science, v. 325, p. 820-821

Neanderthals few on the ground

Analysis of DNA from Neanderthal bones is gathering pace as cheaper and more reliable methods for sequencing emerge. The latest breakthrough is by a team working in Svante Pääbo’s lab at the Max-Planck Instuitute for Evolutionary Anthropology in Leipzig, Germany, which has defined full mitochondrial DNA sequences for five individuals (Briggs, A.W. and 17 others 2009. Targeted retrieval and analysis of five Neandertal mtDN genomes. Science, v. 325, p. 318-321). The samples are from almost the full geographic range known for Neanderthals, from Spain in the west to the eastern shore of the Black Sea in Russia, and are from 38 to 70 ka old; i.e. probably pre-dating the main influx of fully modern humans into Europe. The results show that the range of genetic diversity in the female line was only one third that found in humans today. That suggests that, compared with the modern human diaspora from Africa, total numbers of Neanderthals was low over the period analysed, and perhaps since their first colonisation of Europe and the Eurasian steppes around 400 ka.

See also: Wong, K. 2009. Twilight of the Neandertals. Scientific American, v. 301 (August 2009), p34-39.

Klondike gold rush pays dividends for Pleistocene

The 1896 discovery of gold in the Yukon Territory, Canada triggered the Klondike gold rush, which led to environmental wreckage that continues to this day. The placer deposits are in permanently frozen, but fragile alluvial sediments dating back as far as 700 ka. But as well as gold washed in by the Yukon’s rivers, the permafrost contains exceptionally well preserved records of the area’s late Pleistocene flora and fauna. The reason why that was possible at such high latitude (65ºN) through 6 or 7 glacial interglacial cycles is that it remained free of ice sheets for most of the Pleistocene. Fossils finds in the placer deposits therefore document the conditions on the western edge of the Bering Straits land bridge, or Beringia, which emerged each time that sea level fell during glacial maxima (Froese, D.G. et al. 2009. The Klondike goldfields and Pleistocene environments of Beringia. GSA Today, v. 19 (August 2009), p. 4-10). Beringia was the route presented to the earliest Asian human migrants into the Americas, possibly even before the Last Glacial Maximum 22 ka ago. Much of the evidence comes from wind-blown loess deposits that are prone to permafrost development. Also, being close to a number of active volcanoes the area was sporadically blanketed by ash deposits that are dateable by radiometric means, so a stratigraphy is possible even in the irregular and ice-disturbed sediments. During glacial episodes the area was steppe dominated by herds of bison, mammoths and horses; clearly a hunters paradise, despite the harsh conditions.

Much of the interpretation of the growing database of human genetic variability has so far focused on migration out of Africa and across the habitable continents. To some extent the largest variability, of Africans themselves, has been undersampled, but a multinational team of Africans and non-Africans has now begun to redress the balance (Tishkoff and 24 others 2009. The genetic structure and history of Africans and African Americans. Science, v. 324, p. 1025-1043) partly to study genetically-linked epidemiology and partly anthropology. The study centres on African’s own ideas about their identity/ethnicity as well as documented cultural and linguistic division, and covers 3194 individuals from 121 populations in the continent, African-American populations in 4 US cities and 60 other populations from outside Africa. The team expands knowledge tremendously, as expressed by the many intricate diagrams. They use the statistical method of Bayesian clustering to tease out the ancestral bases for the genetic patterns preserved by Africans, which appear to be based on 14 major ancestral groups that mostly tally with cultural and linguistic divisions. Overall, the picture is one of repeated mixing of populations through migrations within the continent, many within historic times such as the shift of West Africans south-eastwards, but also much earlier movements such as the ancestors of the San people of southern Africa. These remaining gatherer-hunter people together with central African pygmies and the Hadza and Sandawe of Tanzania share ancestry and also, except for pygmies, language that involves click-sounds – the pygmies abandoned their original language in favour of that of the groups that now surround them in the Equatorial rain forests. Of the three groups, the Hadza most maintain the genetic structure of the earliest ancestors on the continent, but all three shared a common ancestor about 35 Ka ago. Interestingly, comparison with people outside Africa confirms earlier studies that indicated a source population for the out-of-Africa migration in East Africa close to the Red Sea.  The paper is necessarily condensed and so difficult to follow, but clearly opens up great vistas in understanding intricacies at which anthropologists have previously only guessed. Like the physical landscape of Africa, that of its population reflects the range of factors that have shaped human evolution and hence a great deal of its destiny.

See also: Gibbons, A. 2009. African’s deep genetic roots reveal their evolutionary story. Science, v. 324, p. 575.

Very old human footprints in Mexico?

In 2006 palaeoanthropologists in the Americas, already at loggerheads about evidence for pre-Clovis (pre 13 ka) colonisation, were rocked to their boots. A team from Liverpool John Moores University, Bournemouth University and the Mexican Geophysics Institute claimed to have found human footprints more than 40 ka old in a volcanic ash deposit (Gonzalez, S. et al. 2006. Human footprints in Central Mexico older than 40,000 years. Quaternary Science Reviews, v. 25, p. 201-222).  The extensive site exposed by quarrying carries many apparent footprints, both human and non-human. Moreover, some of the prints are in convincing-looking trackways. The very old date was obtained by optically stimulated luminescence dating of quartz-grains  that measures the time since the grains were last exposed to sunlight or thermal baking. Were it not for that result probably little fuss would have been made. Now this remarkable find is under serious challenge (Feinberg, J.M. et al. 2009. Age constrains on alleged ‘footprints’ in the Xa;nene Tuff near Puebla, Mexico. Geology, v. 37, p. 267-270). This US-Mexican team applied Ar-Ar dating to the ash and found an age of about 1.3 Ma, confirmed by its association with reversed magnetic polarity in the deposit – at 40 ka the geomagnetic field was as it is today. On that basis, Feinberg and colleagues claim to have refuted the identification of human footprints, and claim that they are merely quarrying marks degraded by later weathering. The Xalnene Tuff in which the footprints were found was deposited in a lake that has been periodically filled and dried out. If the disputed features can be shown irrefutably to be footprints, then there are only two possibilities: either they date from a 40 ka lowstand when the tuff was rewetted and soft, or they are of Homo erectus who somehow found their way to the Americas after leaving Africa around 1.7 Ma ago and crossed the drying lake bed shortly after the tuff was ejected from a nearby volcano.

‘Hobbit’ news

Bones of at least 6 or 7 small people have turned up in the now famous Liang Bua cave on the island of Flores, Indonesia. Their stratigraphic positions span the period from 95 to 17 ka. There have been numerous claims that they do not represent a dwarfed human species – i.e. Homo floresiensis – but individuals who suffered from some form of pathological condition. The strongest evidence supporting that sceptical view is that the one near-complete skull does not fall on the well-established brain –body-size distribution that covers many species: it seems too small for either a normal pigmy modern human or a similarly diminutive H. erectus. Now crucial new anatomical evidence seems set to swing the balance. (Jungers, W.L. et al. 2009. The foot of Homo floresiensis. Nature, v. 459, p. 81-84; Weston, E.N. & Lister A.M. 2009. Insular dwarfism in hippos and a model for brain size reduction in Homo floresiensis. Nature, v.  459, p. 85-88). The foot bones of the most recent and most complete specimen are not like those of humans but more ape-like, although they show clear evidence of bipedalism. Interestingly, they seem to be more primitive than those of H. erectus, raising the possibility of an undocumented dispersal of perhaps from Africa into Eurasia as an ultimate ancestor. Curiously, the foot is disproportionately long compared with the rest of the skeleton; another bonus for ‘hobbit’ fans. Not having a snout, H. floresiensis certainly was no ape, indeed the skull is best expressed as a scaled-down version of either H. erectus or H. habilis. As to extremely small brain size in relation to the body size of H. floresiensis, insular dwarfism of fossil hippos in Madagascar provides a useful analogue, as Weston and Lister suggest. In adulthood they also have disproportionately small brains. As with many puzzles in human evolution, the stir caused by these new discoveries maintains H. floresiensis as a ‘hot topic’ and further excavations are inevitable – Flores has plenty of caves, as do many islands in the Indonesian chain.

See also: Lieberman, D.E. 2009. H. floresiensis from head to toe. Nature, v.  459, p. 41-42.