Category: Anthropology and Geoarchaeology

At the end of October 2004 the front pages of newspapers world-wide carried a major geoscientific story; not about some natural disaster but the discovery of astonishingly tiny people who shared an island with us “big ‘uns” not so long ago.  They were not pygmies, but an entirely different hominin species from ours (Brown, P et al. 2004.  A new small-bodied hominin from the Late Pleistocene of Flores, Indonesia.  Nature, v. 431, p. 1055-1061; Morwood, M.J. et al. 2004.  Archaeology and age of a new hominin from Flores in eastern Indonesia.  Nature, v. 431, p. 1087-1091).  That the species came to light at all is down to the skill of Indonesian archaeologist Thomas Sutikna and his team of workers, who found the most important remains.  The bones had the consistency of putty, because the find was made in a cave in humid tropical rain forest and fossilisation had not begun.  By being treating with a glue, oddly known as “Tarzan’s Grip”  the remains survived excavation to be analysed in the lab.  About one third the size of a modern human’s, the skull was at first suspected to be that of an infant Homo sapiens.  Even cursory examination proved beyond doubt that it was not.  It carries worn adult molars, has no chin and possesses clear brow ridges.  Limb bones suggest a stature around 1 metre (by far the smallest member of the human family), with proportionately longer arms than ours.  Leaving aside the sheer tinyness of this roughly 20-year old female, these features most resemble Asian H. erectus, whose remains from mainland Asia and the larger Indonesian islands date from before 1.5 Ma to possibly as late as 20 ka. 

Dates from the whole suite of Homo floresiensis remains show a remarkably long occupation of Flores, certainly for most of the last glacial period until 18 ka, and perhaps extending back 840 thousand years and to as recent as the early Holocene.  For the later part of their occupancy members of H . floresiensis must have shared the densely forested island with modern people, who arrived there between 35 to 55 ka ago.  How the little people arrived is a problem.  Unlike the western Indonesian islands of Sumatra and Java, which would have been connected to Asia by land bridges during periods of glacial low sea levels, Flores and the eastern Indonesian chain of small islands are surrounded by water that is deeper than 200 metres.  Even the greatest extent of continental ice during the Pleistocene could not have drawn off enough sea water to create a dry passage from Java, and Flores is not adjacent to that known home of H. erectus, but separated from it by the islands of Sumbawa and Komodo, and more deep channels.  Together with the hominin remains in the cave are bones of the notorious Komodo Dragon, rats as big as dogs and minuscule elephants, so the original colonisers could have drifted from Java on floating vegetation rafts in the same way as the precursors of these other animals.  Unlike rats, monitor lizards and elephants, it is unlikely that they swam the necessary 150 km, and there are no records of pre-modern human boats.  Whatever, new arrivals on small islands find totally different conditions from those on larger ones or continents.  Potential food is limited, yet predators are fewer.  There is a well-known tendency for evolutionary miniaturisation of larger mammals, the tiny elephant Stegodon found in the same cave being a case in point.  In general it is reckoned that small-island mammals tend towards a size that is equivalent to a very large rabbit.  Not so for lizards, and the Komodo Dragon, still a terrifying predator on the eponymous island, would have been top of the food chain on Flores.

Another puzzling feature of H. floresiensis is that despite having brains the size of a grapefruit (roughly the size of those of australopithecines), they seem to have used both sophisticated tools and fire.  They were not dim-witted.  Their overlap with modern humans for so long is also intriguing.  In Europe the Neanderthals, physically more than a match for any modern human, drifted to extinction within about 5 thousand years after first encounters.  On Flores, the truly diminutive H. floresiensis clung on for far longer, possibly because resources were much richer than in frigid high latitudes.  Local people throughout eastern Indonesia today tell legends of the little people they call Ebo Go Go.  Perhaps they survived into far more recent times.  Undoubtedly, the dense forests and innumerable caves of the island chain may have other surprises in store.  For the moment, there can be none greater than finding that modern humans walked the Earth with at least two other human species not that long ago.  Nor is that of scientific interest alone.  As the editorial in New Scientist of 30 October 2004 observes, “…Homo floresiensis throws into doubt many of our assumptions about intelligence”.  They lived just as successfully as modern human colonisers of Flores for tens of thousands of years, despite the competition and possibly worse.  So brain size may not be the key to cleverness on which we pride ourselves.  Nor are we as unique as we generally suppose.  As with Tolkien’s hobbits, we should be humbled by their tenacity.

Anthropological nit picking

The chances of extracting human DNA from old bones to compare with that in modern populations are pretty slim.  It has been done for two Neanderthal specimens, and showed that living humans carry no sign of their involvement in producing hybrid offspring fit enough to pass genes upwards through the generations since about 35 ka ago.  Preservation of such molecular material requires extra-special conditions.  But there may be another way, which has a flavour of the opening sequences in Jurassic Park, where dinosaurs were cloned from blood preserved with their parasites in amber.  Body and hair lice are species-specific (we do get bitten by fleas from rabbits, cats and rats, but not by their lice), and the beasts prefer hosts who live cheek by jowl together.  Hair lice are especially good, because as any parent knows they leap as soon as kids get in a huddle, but no more than a few centimetres.  Comparing hair lice from modern humans and chimpanzees, Dale Clayton and David Reed of the University of Utah were able to show by comparing their mitochondrial DNA that the two species’ origins are about as old as the >5 Ma split between the human and chimp evolutionary clades.  Taking the method a step further to compare human head lice an astonishing feature emerged (Reed D.L. 2004. Genetic Analysis of Lice Supports Direct Contact between Modern and Archaic Humans. Public Library of Science:Biology v. 2, e340).  There are two genetically distinct groups in the species Pediculus humanus.  One has a global distribution and infests head and body hair, the other only being found in the Americas and is found exclusively on the scalp.  Their mtDNA molecular clocks suggest a divergence more than a million years ago.  Although they parasitise modern humans, they diverged before even archaic humans appeared on the scene.  The authors suggest that the divergence might have coincided with the separation of the two main populations of Homo erectus, an Africa one that evolved to modern humans and that in Asia, which probably was not on the human clade.  For one human species to carry two subgroups of anciently separated lice suggests that our ancestors went “head to head” with H. erectus, once in Africa and then perhaps much later in Asia, en route to the Americas.  The next step concerns considerably more intimate intra-species contact;  the team is going to investigate the different genus of human pubic lice…..  The collection process may well be underway as I write.

The perils of genealogy

With all kinds of public records on the web and others easily accessible from registry offices etc., tracing one’s ancestry has never been easier, should you be bitten by the family-tree bug.  Genealogy is addictive, out of a sense of adventure, a desire to “belong”, the possibility of tracking down untold riches because a maiden great-great aunt died intestate and her millions were invested in blue-chip stock to await your appearance at the trustees’ door, or because train-spotting has lost its frisson of excitement.  I suspect that there are times when “googling” is slow because genealogist are on line.  There is an old chestnut that if your researches successfully reach back far enough, you will find that William of Normandy or Eric Bloodaxe is a direct ancestor.  In fact research into human Y-chromosome DNA shows very clearly that Genghis Khan and his near relatives dominate the genes of millions of men in parts of Central Asia (see Darwinian evolution of humans challenged by Y-chromosome data? in EPN, March 2003).  That is  special case, as the eponymous warlord slaughtered most of the men in conquered areas and put most of the women into concubinage, and made damned sure that only he and his male kin had droit de seigneur, or its Mongol equivalent.  Simple arithmetic suggests that the chestnut holds true.  Going back generation by generation all of us have 2, 4, 8, 16, 32, and so on, direct ancestors.  The algorithm is simply 2ⁿ, where n is the number of generations.  Say a generation is 25 years, a millennium ago our ancestors would be 40 generations back.  Each of us would have had a trillion such great-great-great-great— grandparents on this simple basis, half men and half women.  Well, there would have to be 500 billion women, but maybe less men, if Genghis’ unwholesome habits were common.  Of course it is more complicated than that, because human populations are separated geographically, and in the past encounters would have been between relatively few travellers.  In fact, for some populations, such as those of pre-colonial Tasmania, contact had been cut off many millennia ago.  Because of the varied evidence for ancestors from whom all humans are genetically descended, such as “African Eve” (>150 ka) and “Big Daddy” (more recently), it is tempting to develop sophisticated models for genealogy (Rohde, D.L.T et al. 2004.  Modelling the recent common ancestry of all living humans.  Nature, v. 431, p. 562-566).  Leaving aside very isolated populations, such as the aboriginal Tasmans, the modelling suggests all of us only need to go back to about 3000 BC to find the ultimate tip of our family tree – our universal, identical ancestor. Anyone else who lived at that time sadly might seem to have had no effect whatever on our generation.  However, pedigree is not necessarily something that would justify you putting a coat of arms on your living room wall.  What we are genetically is not the same as suggested by our family tree.  Further up the tree, the less chance there is that someone appearing in it passed on any genes whatever to you or me.  The exponential law of genealogy no longer works, and the number of our genetic ancestors increases far more slowly.  A proper search for who in your past helped determine what you are requires DNA from everybody, and I don’t see many family-tree fanatics queuing to have their cheek cells swabbed, and nor will I.  I am quite happy that whomever passed on my patrilineal family name was probably one of William the Conqueror’s spear carriers in 1066.  The genealogy goes cold not many generations back, as, in my father’s words, “they were all probably illiterate anyway”!

See also:  Hein, J. 2004.  Pedigrees for all humanity.  Nature, v. 431, p. 518-519.

One of the unique features of humanity is the progress of women into infertility after the onset of the menopause.  Females of all other animal species, including primates, remain potentially fertile until they die, even when kept alive in zoos well beyond their natural life spans.  When the menopause arose is difficult, if not impossible to judge, but the advantage of surviving grandparents, especially grannies released from the burden of child-bearing and care, is huge.  They carry knowledge from two generations or more before the lives of their descendants, and they have the time to confer it on children.  Once grandparents became common members of families, effectively they would have doubled the potential for teaching and learning.  That has immense importance for human survival and development.  In 1990 I witnessed this in action in a remote and war-torn part of Eritrea.  There was a drought worse than any since 1918, and villagers were frantically searching for drinking water for themselves and their livestock, to the extent that they were felling giant baobab trees, more than 300 years old, to get to their water-rich inner core.  While we were attempting, with little success, to advise a group on where to dig a new well a young boy with a large camel arrived.  On it was a couple well into their 80s.  They directed attention to a particular spot, digging resumed, and after 2 hours water was struck. That place was where the couple remembered a well being dug in the great drought of 1918.  It is possible to get some idea of when the possible influence of grandparents arose by finding evidence about age distribution in ancient populations.  The further back in time, the more incomplete are human remains.  However, teeth have the highest of all survival chances, and the do carry evidence of the age of the person who chewed with them, from the wear patterns and the presence or absence of late-erupting teeth (Caspari, R. & Lee, S.-H. 2004.  Older age becomes common late in human evolution.  Proceedings of the National Academy of Science, USA, v. 101, p. 10895-10900).  Caspari and Lee’s work used more than 750 samples of  human teeth, dating back to some of the earliest hominids.  The measure that they adopted to assess onset of old age does not increase gradually into more recent times, but undergoes a remarkable jump around 30ka.  Interestingly, this coincides with the explosion of art of the highest quality in Europe.  Was it the oldsters who made that leap or was it their influence that opened up new horizons for their grandchildren.  Other than this remarkable possibility, the opening of culture as we know it is hard to explain.

Black Sea flooding put to test

In the mid-1990s, William Ryan and Walter Pitman of the US Lamont-Doherty Earth Observatory captured a much wider audience than is the normally the case for geoscientists, when they announced evidence from the Black Sea that seemed to confirm legends of the Flood in the Old Testament and the Epic of Gilgamesh.  They claimed that in early Holocene times, the Black Sea was a freshwater lake some 150 m below present sea level.   At the time, global sea level was below the threshold of the floor of the Bosporus, thereby isolating the Black Sea from the world’s oceans.  Yet sea level was rising inexorably as continental ice sheets melted back.  Around 8000 years ago, sea water flooded through the Bosporus to fill the Black Sea to its present level.  Evidence takes the form of submerged beaches and even possible townships (mounds similar to the tells in Turkey and Mesopotamia formed during long-term occupation by Neolithic to Bronze Age cultures).  Other features on the floor of the Black Sea are zones of large sand waves and signs of incision, ascribed by Ryan and Pitman to massive currents when flow began through the Bosporus.  The way in which such flooding might have take progressed is testable using hydraulic modelling, although the topographic parameters are complex (Siddall, M. et al. 2004.  Testing the physical oceanographic implications of the suggested sudden Black Sea infill 8400 years ago.  Paleoceanography, v. 19, PA1024, doi:10.1029/2003PA000903).  The work of Siddall and colleagues suggests a flow rate of 60 thousand m³ s^-1, about that of a river as powerful as the Brahmaputra (see Catastrophic erosion in Tibet, this issue of EPN).  That would have taken around 30 years to fill the Black Sea to its present level; far longer than the Biblical 40 days and nights, but quick enough to force large-scale migration and to live on in legend.  The model fits with the seabed sand waves and channelling, and being based only on known topography and post-glacial sea level rise, rather than the myths, it carries weight scientifically.  However, little is known about the way in which young sediments in the Black Sea basin formed, and proper documentation awaits their coring..

See also:  Schiermeier, Q.  2004.  Noah’s flood.  Nature, v. 430, p. 718-719.

Several articles over the years in EPN have referred to the phenomenal movement of humans from Africa to much higher latitudes in Asia, from as early as 1.8 million years ago.  Although that migration must have been a gradual diffusion rather than with any purpose, even in interglacial periods it took our ancestors into chilly winter climes.  Many palaeoanthropologists have sought evidence for controlled use of fire that would have made survival more likely, but until recently little concrete signs have been found before the last glacial epoch.  Israeli scientists, who have worked on an Acheulian site in the Jordan valley, found evidence of much earlier fire use (Goren-Inbar, N. et al. 2004.  Evidence of hominin control of fire at Gesher Benot Ya’aqov, Israel.  Science, v. 304, p. 725-727).  A 34 m thick sequence of sediment on the shore of an ancient lake contains several tool-bearing horizons, in each of which they found flint artefacts that show signs of having been burned.  There are also fragments of burnt wood.  Were the burned remnants widely distributed they could be accounted for as the result of wildfires, but they occur in clusters.  That strongly suggests hearths and a human origin.   The age of the sequence is indicated by the layers that contain tools and evidence of controlled use of fire lying just above the Brunhes-Matuyama geomagnetic polarity reversal, whose end is dated at 790 thousand years ago, when the most likely inhabitants were Homo erectus.  The thickness of sediment containing the layers with signs of human activity suggests several tens of thousand years occupation of the site.  Some of the burnt vegetation is of edible species.  However, despite finds of animal bones that show signs of having been processed for food, there are no burnt bones.  So, fire may have been used for comfort, but there is no proof of cooking.

One of the most remarkable achievements of early humans (Homo ergaster aka H. erectus) was not their tools, but their migration out of Africa around 1.8 Ma, to reach as far as Indonesia and China.  There is no evidence for that feat having occurred again until fully modern humans arrived in east Asia about 70 ka ago.  The toolkit of Asian “Action Man” is unimpressive, in the sense that it resembles the slightly reshaped broken pebbles of the Oldowan culture, that first appears in the African archaeological record about 2.4 Ma ago.  Development in Africa of the enigmatic and beautiful bi-face or Acheulean axe was after the first Asians had departed, around 1.5 Ma.  So what were these early wanderers like; what did they want?  The decade-long work in China by Noel Boaz, an anatomist from the Ross School of Medicine in New Jersey and anthropologist Russell Ciochon of the University of Iowa will soon appear in their book Dragon Bone Hill, an Ice-Age Saga of Homo Erectus (Oxford University Press), which they preview in the 17 April 2004 issue of New Scientist (p. 32-35).  Boaz and Ciochon have worked mainly in Zhoukoudian near Beijing, a major resource for human remains whose different levels extend back to about 800 thousand years.  Another site in China, Longouppo, contains disputed remains as old as 1.8 Ma, as are Dubois’ famous discoveries of the type specimens of H. erectus by the Solo River in Java.  From the time when Zhoukoudian became famous among Chinese apothecaries as a source of “dragon’s bones” (a mixture of human and other animal remains) there has always been an air of myth about the findings there – a permanent dwelling for hundreds of thousand years, protected from glacial temperature falls by the consistent use of fire.  In essence, the publicised view is that “Peking Man” led a cosy hearthside existence for a very long time indeed.  Boaz and Ciochon tell a different, and more mundane story.  Most bones in  the deposit are those of a great variety of other animals, with disproportionately few of human origin, and those are highly fragmented.  The dominant species is a giant hyena, and many of the bones, including humans, are well gnawed, which is what hyenas do especially well.  There are occasional signs of human occupation and use of fire.  The human remains are encased in layered carbonate flowstone,.  Records of fluctuating d¹⁸O from that matrix, matched against the global time series of climate change, show that occupation was only during interglacials – the site was abandoned or unvisited during the depth of glacial periods.  Some animal bones show cut marks made by stone tools, and it is more likely that H. erectus raided to get remnants of other beasts’ kills, perhaps using fire, rather than being top of the predatory order.  The great surprise throughout Asia is the complete lack of development of stone tools from the primitive culture that arrived there, until as late as 20 to 30 thousand years ago, when Asian H. erectus vanished.  Apart from the stunning breakthrough to the bi-face axe, African erects also had a million-year long cultural stasis – resting on laurels with a vengeance.  Finally, from a number of skulls at Zhoukodian, Boaz and Ciochon have shown signs of trauma.  These are depression fractures, probably not necessarily fatal, but indicate sharp blows to the head with blunt instruments.  Their interpretation is that the Chinese erects settled disputes by bashing heads; so that aspect of culture has not changed a lot since.  Their story is not “politically correct”, but with publication of their book, other palaeoanthropologists can judge it on the basis of the evidence from Dragon Bone Hill.

Faster development of Neanderthals

Go to any horse sale and you will see bidders closely studying the teeth of their prospective purchases; the origin of the saying, “Never look a gift horse in the mouth”.  Teeth show growth ridges, and in grazing animals they are prominent, so that it is possible to judge the age of a horse easily and accurately.  Human teeth are different only in the less obvious signs of growth.  Microscopic examination reveals such records, down to the daily level, although the most prominent features are curious disturbances in their deposition that form approximately weekly.  They appear as ridges on the crowns of teeth.  The variable spacing of these perikymata provides a record of the pace at which adult teeth develop.  In modern humans the spacing becomes very much closer in the later growth history (towards the tooth’s cutting edge) than in its early stages, and reflects the slow development to full adult dentition.  In a painstaking study of hundreds of teeth from Cro Magnon and Neanderthal teeth, Fernando Rozzi of the University of Paris and José Bermudez de Castro of the Spanish National Museum of Natural Sciences have discovered an odd difference in the development rates of Neanderthals (Rozzi, F.V.R & Bermudez de Castro, J.M. 2004.  Surprisingly rapid growth in Neanderthals.  Nature, v. 428, p. 936-939).  The late perikymata of Neanderthals are more widely spaced than in Cro Magnon and modern humans, strongly suggesting that Neanderthals developed to adulthood by about the age of 15, three to five years earlier than us and our immediate ancestors.  As well as confirming that they are a separate species, the results suggest that Neanderthals, while acquiring brains as large, and in some cases even larger than ours, had evolved more rapid maturation and probably a genetically determined shorter adult life.  This would have had some effect on transfer of culture, which in human societies is often the most important value of elderly folk.   The fewer samples of teeth of earlier human species (H. heidelbergensis and H. antecessor) reveal an even greater surprise.  They are more like modern human teeth (albeit with signs of somewhat faster growth), which suggests that evolution of the Neanderthals involved a regression.  The authors suggest that the combination of a backward step to faster development with rapid brain growth to large size might reflect a very-high calorie diet together with adverse environmental conditions.

There is no topic in the geosciences that is more interdisciplinary than that of human origins.  Geologists, anthropologists (social as well as physical), archaeologists, geochemists, linguists, geneticists, dentists, specialists in nutrition and even novelists (for example Jean M. Auel) contribute.  Everyone is interested, and so everyone not only wants to have a say, but somehow to be involved.  Again and again in the pages, it becomes clear that bones and artefacts can no longer make major breaks through.  The Out of Africa hypothesis, although suggested by Charles Darwin and many palaeoanthropologists since, became widely accepted (though not completely) after the evidence for relatedness emerged from comparisons of mitochondrial DNA from women throughout the world.  That showed clear signs of a last common ancestor for all human groups around 200 thousand years ago, to whom modern Africans were most related.  At the end of March 2004 geneticists have again come up with something startling, but this time not guessed at before.

The first beings to whom the generic name Homo seems appropriate appear in the hominid fossil record about 2.0 million years ago.  Apart from evidence for bipedality and their association with rudimentary, but nonetheless deliberately made stone tools, the earliest humans are marked by the fragility and roundness of their skulls.  Many specialists have argued that “gracile” crania are an evolutionary pre-requisite for the growth of brain capacity – they can expand for a long period during development, before becoming completely ossified in adulthood.  The predecessors of these early humans (australopithecines) and their close companions in the African savannahs (paranthropoids) had smaller brain capacity and also very bony heads.  In the case of the paranthropoids, undoubtedly as closely related to earlier hominids as the first tool-making humans were, they survived as a group for another million years but never expanded their brains, nor presumably their intellects.  Bone-headed hominids had one feature in common with all earlier apes, and with the genera that survive today; powerful jaws and muscles that drive them.  To some degree or other they all have crests on top of their skulls, which provide the seats for these big jaw muscles.  Wielding awesome biting power requires skull strength, and therefore bulky bone.  That encumbers any possibility for expansion of the internal brain cavity, and also drives their bearing species into tight feeding habits.

A team of geneticists, anatomists, developmental biologists and plastic surgeons from the University of Pennsylvania and the Children’s’ Hospital of Philadelphia have studied one gene sequence of several that encode for a type of protein (myosin heavy chain) associated with the powerhouse muscles that are attached directly to bone, such as those which drive jaws (Stedman, H.H. and 9 others 2004.  Myosin gene mutation correlates with anatomical changes in the human lineage.  Nature, v. 428, p. 415-418).  Their investigation began with an interest in muscular dystrophy and possible underlying factors.  Specifically, the most interesting gene (MYH16) is expressed in primate jaw muscles.  The human gene contains a mutation that prevents the accumulation of the protein in our jaw muscles, so they cannot be as strong as those of other primates and mammals in general, in which the gene functions as it should.  By analysing MYH16 and related gene sequences in humans from widely separated populations, the researchers showed that the mutation in MYH16 diverged earlier than those in other MYH-related genes.  To estimate the time of that divergence involved detailed analysis of the mutations in other living species – dogs, macaque monkeys, oran-utans and chimpanzees.  This showed that MYH16 evolved under Darwinian selection, conferring fitness advantage, in the ancestral lineages leading to each species, whereas in humans there was no selective constraint.  Under the second condition, it can be assumed that any evolutionarily neutral changes took place at a constant rate.  Calculations suggest that in the human lineage, the mutation appeared 2.4±0.3 Ma ago.  That coincides with the earliest appearance of tools and a little earlier than the first remains of early Homo fossils.  The conclusion could be one of several: lost of biting power created conditions for expansion of a lighter skull; a changed diet to include more meat reduced the need for strong jaws, so that the mutation did not have a deleterious effect; or hands freed by walking upright did a lot of the work that other primates can only accomplish with their mouths.  Whichever, once established without decreasing fitness, the road to enlarged brains and fuller consciousness was opened by a chance event.

See also:  Ananthaswami, A. 2004.  less bite, more brain.  New Scientist, 27 March 2004, p. 7;  Currie, P. 2004.  Muscling in on hominid evolution.  Nature, v. 428, p. 373-374

Dental records of earliest hominids

Conditions on land are not as conducive to preservation of fossil remains as those on the sea floor.  When an animal dies it is generally eaten, what is left rots and is gnawed, and the action of wind and water breaks up the skeleton and transports it, and only this debris is preserved if it is buried by sediment.  The best chance of preservation is if the animal falls in a lake or bog, or in the case of fully modern humans if it is deliberately buried.  The so-called Turkana Boy (H. erectus) is an almost complete skeleton, because he did end up, uneaten, in a swamp.  Sturdy, large animals and those small and light enough to be quickly washed to burial stand the best chance of appearing as complete fossils.  Primates are medium-sized and lightweight, and that presents palaeoanthropologists with their single biggest problem, incompleteness of most fossils that they find.  In the depths of the Afar Depression of Ethiopia and Eritrea, which is the most productive area for hominid specialists, conditions from the early Miocene were not the best for preservation.  While the depression developed by extensional tectonics, its flanks rose to form the mighty Ethiopian escarpment from which torrents flowed seasonally.  High-energy streams clearly will break up any articulated skeleton and batter what is left before they end up in gravels and sands on the floor of the depression.  So it is a credit to the patience, experience and sheer visual acuity of those who work there that they can piece together the earliest parts of the human story.  Yohannes Haile-Selassie, Gen Suwa and Tim White have pushed back and detailed our record further than any other group, thanks in part to the richness of the Miocene to Recent Middle Awash sedimentary and volcanic sequence with which they work.  In 2001 Haile-Selassie discovered the earliest Afar hominid so far (see Taking stock of hominid evolution, March 2002 issue of EPN), Ardepithecus ramidus kadabba dated between 5.2 and 5.8 Ma.  In age it roughly matches Sahelanthropus and Orrorin from Chad and Kenya.  Only a leg bone from Orrorin gives some indication that it was bipedal, but all show cranial features that mark them out as probable hominids.  Of all the body parts of any animal, the teeth are the most likely to survive with little change.  Because our closest living relative are chimps, comparing early teeth with theirs, as well as with those of later hominids, is about the best that can be done to seek relatedness.  The three notable workers on Awash hominds have now reported their results (Haile-Selassie, J. et al. 2004.  Late Miocene teeth from Middle Awash, Ethiopia, and early hominid dental evolution.  Science, v. 303, p. 1503-1505), which suggest the earlier find is a distinct species A. kadabba.  Putting together upper and lower canines and adjacent premolars shows a close resemblance to those of modern chimps.  However, it requires detailed measurements of the tooth shapes to check if the resemblance is more than superficial, and it is not.  All extinct and modern apes show signs of automatic honing of their canines, whereas hominids do not.  Not only A. kadabba but Orrorin and Sahelanthropus too, show no sign of canine honing.  That points to early members of human evolution.  Yet, the three show such close similarity that it is hard to support the idea that they are from anatomically different genera, despite their occurrence thousands of kilometres apart.  It is that close resemblance (and in other features as well) that re-opens the long debate between a complex, messy “bush” of human descent made up of many contemporary, different creatures, and one of a single line of descent.  Dental features are not enough to decide between the two.

Seven and a half years after the discovery of a 9300-year old human skeleton in Columbia River alluvium in Washington state, USA, researchers may finally be able to study the remains.  So-called Kennewick Man caused a storm when first unearthed, for his skull was very different from that of any other early American colonist.  Indeed, partial studies suggested close resemblance to Europeans.  Four Native American tribes in the Pacific Northwest claimed the skeleton for reburial, under the Native American Graves Protection and Repatriation Act.  The move was not entirely connected with respect for sacred rites.  Evidence that the area might have been first colonised by people who were not related to the tribes living there just before European occupation in the 19^th century could undermine claims for mineral and other land rights by native people.  On 4 February 2004 a San Francisco court ruled that the remains were so different from any North American indigenous people, that the claimants had no rights over them.  Studies of a skull cast of Kennewick Man since he was placed under lock and key now suggest a possible origin from Asian hunter-gatherers similar to the Ainu people of modern Japan.  However, modern techniques of genetic analysis and isotopic studies of tooth enamel that could settle the issue of origin and relatedness require the original material.  Interestingly, a spear point is lodged in the pelvis, so, like the famous Ice Man of the Italian-Austrian Alps, Kennewick Man may have been the victim of either a deadly dispute or ritual killing.

The use of radiometric dating based on the decaying away of radioactive ¹⁴C is the most useful technique for building sensible archaeological and climatic records over the last 50 thousand years.  However, this radiocarbon is produced from ¹⁴N by cosmic rays in the upper atmosphere, and their flux varies with time.  Consequently, the proportion of ¹⁴C in the environment varied in the past, and a radiocarbon age is not necessarily an age in calendar years “before present” (BP).  Even BP is confusing, because it isn’t “before now” but before 1950 when the first hydrogen bombs produced ¹⁴C.  The outcome is one of some confusion.  If dates were recorded in calendar years, whether BP or AD/BC everything would be clear.  But they aren’t.  Many authors give their dating as either ¹⁴C ages (BP) or calendar years (BP), and the two can be very different.  For instance, the date when the Younger Dryas glacial pulse began is 1000 calendar years older than its ¹⁴C age.    One reason for the dichotomy is that no agreed conversion existed until about 1998, particularly for the time before which annual growth rings in trees can be built into an unambiguous record, using modern trees and those preserved in ancient timber.  Bristlecone pines and other long-lived trees first gave an accepted conversion factor that went back around 6000 years.  That has been extended to about 26 ka by dating annually layered corals, stalagmites (speleothem) and sediments.  A way of going even further back is correlating large, world-wide events between their appearance in a record such as a marine sediment core, dated using ¹⁴C, and their appearance in a Greenland ice core, whose annual layering gives a calendar age.  However, further back in time less radioactive ¹⁴C remains to be measured and contamination by later carbon introduced by percolating water blurs the dating.  In September 2003 the 18^th International Radiocarbon Conference tried to clear the air (Bard E. et al. 2004.  A better radiocarbon clock.  Science, v. 303, p. 178-179).  The latest “official” calibration curve, (INTCAL04) goes back to 26 ka.  But beyond that there are 3 quite different candidates for calibration, the sea-floor sediment-ice core curve, one based on annually layered lake sediments in Japan, and one from speleothem in a submerged cave in the Bahamas.  For a vitally important archaeological find, such as the paintings in the Chauvet cave in France, the ¹⁴C date of 31ka could range from 33 to 38 ka in calendar years.  Dates for fossil occurrences of Neanderthal and the first fully human Europeans could overlap or be so different that neither had an influence on the other.  Everyone hopes that the sea-floor sediment-ice core curve can be validated by new results, thereby giving a common age framework to all dateable materials.

In 1991 archaeologists working at the Georgian site of Dmanisi, which had been an important town on the Silk Road, found human remains, but they lay beneath the level at which several extinct mammals had been found.  As work progressed in the deeper levels, head bones emerged.  They were exceedingly primitive, and associated with equally archaic tools; not the elegant biface stone tools of Homo erectus and later, truly human people, but from the Oldowan culture found with the earliest Homo habilis in Tanzania.  The first estimate of their age, based on the mammal remains, was 1.6 Ma.  Apart from disputed finds in Indonesia and China, the Dmanisi hominids were the oldest found outside of Africa.  Yet at that time, the larger, more brainy H. erectus was thriving in Africa, using the Acheulean biface axes.  For the Georgian archaeologists, and the growing number of international collaborators, 9 years of painstaking work lay ahead before enough data had been gathered to draw conclusions confidently.  A well illustrated summary of what Dmanisi has revealed appeared in the November issue of Scientific American ( Wong, K. 2003.  Stranger in a new land.  Scientific American, v. 289(5), p. 54-63).  Lots fell into place, when eventually the stratigraphic position of the hominid remains was convincingly established using radiometric dating of basalts below and above it – 1.85 and 1.76 Ma respectively.  With more cranial fossils, the Georgian team led by David Lordipanidze the late Leo Gabunia were able to show just how primitive the Dmanisi hominids were.  Their brain capacity was half that of modern humans, and detailed skull features resembled the earliest known member of the human genus, H. habilis.  They were small people too, and palaeoanthropologists really cannot decide whether they were australopithecines or part of our genus.  Lordipanidze believes that they are transitional between habilines and erects.  What is most surprising is that they migrated as far as Georgia.  That would have involved either crossing the mountains of Turkey and Iran, or, had they taken the possible route out of Africa across the Straits of Bab el Mandab (possibly dry land at the time), an even more circuitous route following the coast of Arabia and perhaps up the Tigris-Euphrates rivers.  Their journey began before H. erectus invented the biface axe, which up to now has been regarded as the first sign of both a leap in intellect and the beginning of some command over the rest of nature.  The Dmanisi hominids made it and survived, despite their apparently puny frames, if the abundance of animal bones at the site marks long occupation.

Science continues its occasional series on individuals who make an impact on the progress of science with a review of the growing number of Africans working at the forefront of human evolutionary studies (Gibbons, A. 2003.  Africans begin to make their mark in human-origins research.  Science, v.  301, p. 1178-1179). Ethiopians, Kenyans, Tanzanians and Eritreans have all made important finds and published their results over the last decade.  Their hallmark is avid field work, backed up with growing interpretative skills.  All credit the encouragement they have had from western colleagues, but now they are in a position to bring along a new generation of experts in their home countries.

The “Big Daddy” theory of human evolution!

One of the anthropological shocks of the 21^st century was the discovery that the gene pool of central Asian men is dominated by such a limited range of Y-chromosome  characteristics that the only conclusion is that one small group of closely related men dominated impregnation across the region about 800 years ago.  They were probably all Mongols closely related to Genghis Khan (see, Darwinian evolution of humans challenged by Y-chromosome data? EPN March 2003).  Studies by geneticists from Italy, Portugal and Spain recently suggested that sexual dominance by very few men may have been widespread before about 18 to 12 thousand years ago, around the beginning of the warming that closed the last glacial epoch (Dupanloup, I. et al. 2003.  A recent shift from polygyny to monogamy in humans is suggested by the analysis of worldwide Y-chromosome diversity.  Journal of Molecular Evolution, v. 57, p. 85-97).  Mitochondrial (passed maternally) and Y-chromosome (paternal) DNA studies have been key tools in explaining the timing of migrations of humans over the last 100 thousand years, since their genetic patterns seem to cluster regionally.  Molecular clock estimates that use the appearance of new genetic mutations indicate the timing of population separations.  The study by Doupanloup and colleagues examined data from individuals who live on all continents.  There is an odd and generally distributed difference in genetic diversity between mitochondrial and Y-chromosome DNA, which superficially suggests far more women than men during the last glacial epoch.  In terms of births, that is clearly impossible.  One explanation, favoured by Doupanloup et al., is widespread polygamy that dwarfs that which notoriously occurs within some religious sects today.  Moreover, the “privilege” would have had to be passed on to successive generations of men directly related to the original “Big Daddies”.  Rapid shifts in power would not have left such a clear imprint on global Y-chromosomes.   How that was achieved without repression or slaughter of potentially competing men, is impossible to judge.  However, probable changes in EuropeanY-chromosome patterns around 70, 40 and 20 thousand years ago, that have been ascribed to either evolutionary “bottlenecks” during periods of rapidly dwindling numbers or sudden migrations, might equally have been due to the rise of new patterns of a few males’ dominance over others.   Dupanloup et al. show that the rise of agriculture around 10 thousand years ago seems to coincide with a breakdown of massive polygamy and more common monogamy.  There are other possible interpretations of the data.  In a largely monogamous society, if males stayed where they were born while women moved to live in their mates’ home area, men would be closely related to others in their area, eventually resulting in very similar Y-chromosomes being shared by many.  Different migration patterns or early deaths for most men while hunting may also have led to the genetic bias that is causing great discussion among evolutionary geneticists.

Source:  Bhattacharya, S. & Le Page, M. 2003.  A few prehistoric men had all the children.  New Scientist, 6 September 2003, p. 18.

Ras Tefari Makkonnen (Haile Selassie) claimed direct descent from the illicit liaison between Solomon and the Queen of Sheba, several millennia before his reign over Ethiopia.  Now, “everyone knows” that we are all descended from a single African woman who lived about 120 to 150 thousand years ago – only the line of descent from her proved continually fertile and survived until now.  So, it is perhaps fitting that the earliest known remains of properly modern human beings have emerged from the soil of Ethiopia, in the highly fossiliferous sediments associated with the Awash river that drains into the Afar Depression.  The cover of Nature (12 June 2003) shows a forensic reconstruction from a male skull found at Herto Bouri, and it bears an uncanny resemblance to the handsome fellows who roam with their herds in modern Afar.  There the resemblance stops, for the Afar are not truly African but hale from Arabia, as do many other Ethiopians.  These human fossils are 160 thousand years old, and may be contemporary with “African Eve”, or even earlier.  The issue of “modernity”, as with others based on anatomical features in incomplete fossil remains, is a bone destined to be gnawed at continually.  The discovering team was led by Tim White of the University of California, who regular readers of Earth Pages News will recall came up with the shocking suggestion that deformation of hominid remains could underlie a profligate splitting of human evolution since 4 Ma into many species, some of which might be spurious, even capricious (Ancestral lines squashed?, in EPN of May 2003).  The central feature of the well-preserved and undeformed Herto fossils is that they look modern, yet pre-date the classic Neanderthals of Europe (White, T.D. and 6 others 2003.  Pleistocene Homo sapiens from Middle Awash, Ethiopia.  Nature, v. 423, p. 742-747).  The paper shows nicely, by photographic comparison, how the 160 ka humans lie between the more heavily browed archaic H. sapiens from Ethiopia and Zimbabwe (ca 500 ka) and 100 ka humans from Israel.  However, statistical plots show graphically the limited number of specimens that palaeoanthropologists have to grapple with, even for relatively recent hominids.  Modern as they appear, the Herto fossils lie outside the spread of morphologies gleaned from anatomical studies of Holocene humans.  But they do have an astonishingly human characteristic.

All three crania, two adult males and an infant, show clear signs of cut marks (Clark, J.D. and 12 others 2003.  Stratigraphic, chronological and behavioural contexts of Pleistocene Homo sapiens from Middle Awash, Ethiopia.  Nature, v. 423, p. 747-752).  It appears as if the heads of the individuals were cleaned of any skin and flesh, probably by scraping with extremely sharp obsidian blades.  The infant cranium is also polished, as if it had been carried around for a long period.  Since the markings are very different from those produced by preparing carcasses for eating, and in any case only the brain is a substantial object for cannibalism of a human head, these marks must signify some post-mortem ritual.

The Sterkfontein Caves near Johannesburg in South Africa have provided some of the best preserved hominid remains, because they are enveloped in chemically precipitated cement.  Fossils are also much more plentiful than at other sites, and the caves have yielded about 500 specimens.  However, unlike sites in bedded sediments interleaved with volcanic horizons, cave deposits are difficult to date accurately.  Up to now, correlation of other fossil animals in the breccias that encase Sterkfontein hominids with those at more amenable sites, together with dating based on palaeomagnetic reversals, have been hotly disputed.  A new technique based on the radioactive decay of isotopes that cosmic-ray bombardment induces in quartz grains promises to resolve the paradox of wonderful fossils that cannot be dated.  While quartz grains are at the surface, in alluvium or the debris on slopes, cosmic rays produce radioactive aluminium and beryllium isotopes in a fixed proportion.  The longer the exposure time, the more radioactive isotopes are produced.  But if such irradiated grains are buried, the isotopes decay away, because they are protected by overlying material.  Detrital sediments enter cave systems very quickly, so they are near-ideal for the use of cosmogenic dating.  Of the two most-used isotopes, ²⁶Al decays quicker than ¹⁰Be.  So, the ²⁶Al/¹⁰Be ratio decreases with time and gives a measure of how long the sediment has been buried.  Results from Sterkfontein (Partridge, T.C. et al. 2003.  Lower Pliocene hominid remains from Sterkfontein.  Science, v. 300, p. 607-612) show that the stratigraphically lowest fossils are much older than previously thought; around 4 Ma..  Previous age estimates suggested that the oldest Sterkfontein hominids lived around the same time as Australopithecus afarensis, of which the famous “Lucy” skeleton was an Ethiopian member.  Four million years ago A. anamensis would have been a contemporary, yet the hominids at Sterkfontein seem quite different anatomically.  Maybe there were two species in Pliocene Africa, one East African and the other a southern one.  In fact, there are hints that perhaps two species of australopithecines, along with a more robust paranthropoid may have been washed into the caves.  There are two problems though: cosmogenic dating is notoriously imprecise (the age reported is 4.2±0.3 Ma), and Sterkfontein has such excellent preservation that the number of specimens outweighs those from elsewhere – comparisons are not easy!

Tracking migrations with language

One of the first surprises that arose when genetic relatedness among living people and the estimated time of their separation began to encompass global populations was how well the genetic patterns matched with the distribution of the world’s languages.  When populations move they not only carry their genetic heritage but their languages.  Probably the greatest migrations in human evolution took place at the end of the last Ice Age, and so it might seem that plotting language distribution ought to chart the paths these wandering people took.  Jared Diamond and Peter Bellwood (Diamond, J. & Bellwood, P. 2003.  Farmers and their languages: the first expansions.  Science, v. 300, p. 597-603) have reviewed just how complex such a task will be.  Genes and language can tell only part of the story, because people carry skills and culture too.  The two dominant cultures around 11 000 years ago were the age-old ways of the hunter-gatherer and the new agriculture and animal husbandry.  There are at least five possibilities involved.  Genes, language and lifestyle could mix between both groups when they came into contact.  Hunters might take up farming but keep their identity.  Hunters were as likely to shift as farmers when climate belts changed.  Powerful incomers might impose their language but not their genes.  When one group moved, another might take its place.  Bearing in mind these caveats, Diamond and Bellwood review the main patterns of linguistic groups, using excellent graphics.

Many of the famous finds of hominid crania, on which ideas of human descent hang, consist of small fragments that have to be glued together to reconstruct their form.  The basic work of palaeoanthropology is very like doing a 1000-piece jigsaw puzzle, but in three dimensions.  Tim White, one of the pioneers of modern studies of hominin fossils, is now worried that the fragmentation of bone is connected with distortion during burial (White, T. 2003.  Early hominids – diversity or distortion.  Science, v. 299, p. 1994-1997).  His own studies of fossil pigs present a disturbing pattern of post-mortem distortion that spurred earlier workers to subdivide them “exuberantly”.  There are even “flat-headed flat pigs” and “narrow pigs” (literally, from their given Linnean names), but they are now known to be mechanically distorted remains of a single early pig.  Hominid crania viewed in this light, and there are nowhere near as many as those of pigs, are a mess.  White gives one example, Kenyanthropus platyops (“flat face”), which may well be a distorted and quite ordinary Australopithecus afarensis.  Combined with the shape variation within living species, notably humans but also among bonobo chimpanzees, distortion throws the bushy tree of human descent into considerable doubt, just as Jonathon Kingdon predicted 10 years ago in his book Self-Made Man and His Undoing.  There are so few hominid remains, and most are a mess, that it seems impossible to decide whether many hominin species existed together at any one time in the Late Miocene to Early Pleistocene, or that just a few (even one?) spread to many different habitats across the face of Africa; something of a bombshell for those who make a tidy living from skull-hunting and hominin cladistics.

Walking with Slade

Imagine, if you will, the Pliocene savannah of East Africa and a band of upright apes (Australopithecus afarensis), each (even the females) with the trademark sideburns of Noddy Holder.  Imagine too that peeping from the bush is a voyeuristic obstetrician who resembles Groucho Marx, drinking a hot beverage (Cuppasoup?) from a flask, and trying ever so hard to get one over on Whispering David (Attenborough).  There is a story here, because one of the apes is Lucy, who gets clobbered in Pliocene Slade’s fracas with a rival band (Staus Quo?), her infant falling into the long grass.  Her sister rescues the child, and all is well on the long road to humanity.  That was the first episode of the BBC’s Walking With Cavemen, the third series aimed at popularizing palaeontology, which began with Walking with Dinosaurs.  All three owe as much to Bambi and Dumbo as they do to computer animation and modern research, despite the best efforts of the numerous scientific advisors.  I saw the trailer for the next episode, concerning Homo ergaster – quite apt, because that was “Action Man”, that was.  Not only were they white with tangled grey locks, but despite the brow ridges it was hard to conceal the fact that they were Pan’s People and the Chippendales striding purposefully across a salt pan.  Did even female H. ergasters have 6-packs?  Physically arousing it may have been, again leaving out the brow ridges, the bad barnets and table manners, but I thought, “Tripe”, and watched the footy the following week.  (Note: “barnet” – rhyming slang for hair, from Barnet Fair).

A genetic key to human evolution?

It will not be too long before the publication of the chimpanzee genome.  Because chimps are our closest relatives, and we shared an ape ancestor about 5 to 7 Ma ago, there is bound to be a media hullabaloo (and agitation among creationists) on the day of the release.  At first sight, a comparison of human and chimpanzee genomes might seem to offer plain clues about the genetic side of our co-evolution, but evolutionary biologists are not so optimistic about an imminent breakthrough (Carroll, S.B. 2003.  Genetics and the making of Homo sapiens.  Nature, v. 422, p. 849-857).  Their hesitancy stems from a matter of arithmetic and the sheer volume of work that needs to be done, as well as because of gross uncertainties about how genes relate to the important traits of humans and their differences from closely related apes.  The human genome consists of about 3 billion base pairs and the gross difference from that of chimpanzees is about 1.2% (incidentally, it is likely that all mammals, from mice to men, share around 80% of their genes).  Assuming that this difference is split 50:50 between the results of evolution towards us and towards chimps over the last 5 to 7 Ma, the divergence from the genotype of our shared ancestor in the human genome should amount to about 16 million new base pairs.  Some of them may be “chaff”, but the genetic side of human evolution is buried in this massive area of potential work.  Maybe around 200 000 are tied to evolved changes in protein production, that could be the key candidates for research.  Although there have been claims for genes that control this or that side of humanness, properly tying down traits to genes will be an awesome task.

The differences between chimpanzees and humans manifest themselves in anatomy and behaviour, and a huge body of knowledge on both has grown in the last two centuries.  So biologists know pretty well what they are looking for in terms of interesting genotype-phenotype links.  However, a chart of those parts of the genome that account for the differences, whenever that becomes a believable reality, really does not help with the hows and whens of the course taken by evolution over several million years.  They rely on the fossil record.  Astonishingly, chimpanzee fossils are almost totally unknown, especially in the early part of their phylogeny.  Even by the most optimistic account, the record of our predecessors is patchy and only a handful of near-complete skeletons are known from before about 500 ka.  Carroll uses the most “bushy” version of hominin cladistics claimed by palaeoanthropologists, with 19 species, to illustrate the current status of hominin descent.  White’s view of the uncertainties (Ancestral lines squashed?, earlier in this issue) makes the crucial connections before about half a million years ago extremely flimsy.  But, there will undoubtedly be a huge growth in human evolutionary studies, once the key chimpanzee data become available.  Of course there will be a massive media hype as well, and all manner of outlandish claims.  But maybe also more funds for palaeontology will stem from the potential to link the evidence from today’s graspable realities with the exciting though puzzling anatomical record since the late Miocene.

Our churning bowels and stomach mimic a variety of inorganic environments in which a large range of bacteria have thrived for hundreds, if not thousands of million years.  The stomach has low pH thanks to hydrochloric acid, sufficiently strong to make limestone fizz should you be unfortunate enough to throw up while collecting fossils.  Parts of the gut are highly reducing, so that humans contribute their bit to global warming through the action of our symbiotic methanogen bacteria, although much less so than ruminant mammals which are major methane producers.  We also host sulphate-sulphide reducing bacteria, with sometime spectacular effects in enclosed spaces.  The animal gut has been around for quite long enough for internal bacteria to evolve and adapt to the dietary habits of their hosts, mostly as symbionts.  However, some are pathogenic and infective.  One pathogen in particular is not infective, so its effects have remained undetected until recently.  It is now known that a major cause of gastric and duodenal ulcers, and digestive-tract cancers is the Gram-negative bacterium Helicobacter pylori.  Massive doses of acid suppressants and bactericides effect miraculous cures on individuals who have had decades of misery from stomach pain.  Now that the culprit has been fingered, you will not be surprised to learn that its DNA has been studied in some detail.  The results are surprising  (Falush, D. and 17 others 2003.  Traces of human migrations in Helicobacter pylori populations.  Science, v.  299, p. 1582-1585).  Helicobacter is extraordinarily diverse, and regionally distinctive.  Because it is pervasive, but not infective, the bacterium travels along with populations of its hosts, and is therefore a potential tool in tracking migrations.  There are 7 geographically distinct H. pylori groups today, and their genetic structure can be traced to ancestors in Africa, Central and East Asia.  Their geographic distribution matches those of human genetic and linguistic patterns, which have been attributed to the colonization of Polynesia and the Americas, to Neolithic migrations of agricultural peoples into Europe from the near-East, the expansion of Bantu-speaking people in Africa and to the slave trade.

Neanderthal review

The last ten years has seen enormous developments in understanding the first Europeans. So, a review of how they lived, how they differed from us, how they might have thought and how they came to an end shortly after our immediate ancestors turned up is very welcome (Klein, R.C. 2003.  Whither the Neanderthals?  Science, v.  299, p. 1525-1527)

The first volcanologists?

If there is ever a chance, the site that I would most like to visit is that discovered by Mary Leakey near Olduvai Gorge in Tanzania.  A bedding surface in volcanic ash records footprints of two adult australopithecines and a juvenile who trudged together through fresh debris from a nearby volcanic eruption.  The earliest and irrefutable confirmation of bipedalism, the tracks are also among the most poignant in the fossil record of humanity.  Did this family survive the tragedy?  The trackway is now covered to guard against erosion and theft.  Altogether less heart-rending are younger footprints in an ash layer from the Roccamonfina volcano in Italy (Mietto, P. et al. 2003.  Human footprints in Pleistocene volcanic ash.  Nature, v. 422, p. 133), long known to locals as “devils’ trails”.  The ash formed on the slopes of the volcano, as a pyroclastic flow, and the fossilised trail slopes at up to 80º.  Because the ash is about 350 thousand years old, whoever made the prints were not fully modern humans, but probably ancestors of Neanderthals (H. heidelbergensis).  The individuals had quite small feet, and may well have been children.  The tracks come down the slope, both zig-zagging and showing occasional hand prints to steady the descent.  They give the impression that whoever made them was not escaping an eruption, but having fun, much as kids today cannot resist hurling themselves down sand dunes and snow slopes.  There is another possibility: curiosity drove them up the volcano after products of an eruption had cooled.  Volcanologists cannot resist doing that either, and, as today, maybe they went up a little too early for comfort and had to leap for their lives.

See also:  Muir, H. 2003.  Earliest human footprints preserve prehistoric trek.  New Scientist, 15 March 2003, p. 15.

In the February 2001 issue of Earth Pages news, I commented on the extraordinary feat of Australian geneticists’ having extracted mitochondrial DNA from fossil Australians that date back perhaps 60 thousand years (Out of Africa hypothesis confounded?). The oldest not only represents the earliest Australian yet found, but turned out to be very different from that of later inhabitants (Adcock, G.L. et al. 2001.  Mitochondrial DNA sequences in ancient Australians: Implications for modern human origins.  Proceedings of the National Academy of Sciences, v. 98, p. 537-542).  That was “Mungo Man”, named after an archaeological site near Lake Mungo in western New South Wales.  At the time of publication, the date associated with the level in which the skeleton had been found was about 60 ka).  This was so early relative to the evidence for a 70 ka estimated age for the last common male ancestor of DNA in modern humans’ Y chromosomes (one pin in the Out of Africa Hypothesis), that multi-regionalists reckoned that it supported their ideas.  Oddly, the dating, based on thermoluminiscence of quartz, which records the time since grains were last exposed to daylight, used material from 400 metres away from the burial.

In the last few years, thermoluminescence dating has improved.  Using an optically stimulated variant to date sand grains from Mungo Man’s burial, James Bowler and associates from Australia have resolved the problem (Bowler, J.M. and 6 others 2003.  New ages for human occupation and climatic change at Lake Mungo, Australia.  Nature, v. 421, p. 837-840).  The burial was 40 ka ago, late enough for migrations spreading from Africa around 70 ka to have reached Australia.  Bowler and colleagues suggest that first colonisation of Australia was perhaps around 50 ka.  The date also support two other much debated ideas, that humans’ arrival resulted in their eating to extinction most of the large animal species in Australia, and by using scrub burning on a large scale to drive game in the “red centre”, changed the climate to its present arid state.  Mind you, climate change may have been coincidental and arose from global cooling and low-latitude drying as northern ice sheets began to spread in earnest.  Possibly climatic stress drove the first Australians to adopt fire as a hunting tool.  What the new work does not do is set to rest the suspicions for even earlier occupation recorded by artefacts and even stone markings that may be art.  Some workers have suggested that these may date to more than 100 ka, although without a clue as to the creators.

See also:  Young, E. 2003.  Mungo Man has his say on Australia’s first humans.  New Scientist, 22 February 2003, p. 15. 

Darwinian evolution of humans challenged by Y-chromosome data?

This section is usually reserved for items that predate historic times.  However, new work on genetic markers in the Y-chromosomes of Central Asian (from the Pacific to the Caspian Sea) men has revealed an astonishing feature.  Of the 2123 individuals who donated swabbed tissue for Y-chromosome DNA sequencing 8% have almost identical patterns of markers.  Scaled up to the regional population, the data suggest that about 16 million men in the area show this peculiar similarity – about 0.5 % of all living males.  The authors of the study (based in Mongolia, Uzbekistan, China, the UK and Italy) make a strong case for the direct male lineage of this living population having started in Mongolia 1000 years ago, and really getting underway with Genghis Khan’s imperial exploits in the 13^th century (Zerjal, T and 22 Others 2003.  The genetic legacy of the Mongols.  American Journal of Human Genetics, v. 72, p. 717-722).  For the line to have remained so dominant requires “social engineering” on an almost superhuman scale.  Not only must Genghis himself have been the “stud” he is reputed to have been, together with his contemporary, close male relatives and their direct male descendants, but unrelated men of the time in that region must somehow have been excluded from access to local women.  History suggests that was ensured by massacre and bondage on a vast scale throughout the history of the Mongol Empire.

Markers in Y-chromosome DNA arise through mutation, and are highly unlikely to carry any kind of genetically determined trait, least of all a predilection for pillage, murder and rape!  Complex analysis of the distribution of genetic markers in populations leads to ideas about how they arose, their relatedness to other markers, and an estimate of their age relative to one another.  Study of Y-chromosome markers helps understand when a male lineage began.  One such marker is estimated to have first appeared about 70 thousand years ago (see Eve never met Adam in Earth Pages News, November 2000) and occurs in all analysed modern men, giving rise to the notion of a last common male ancestor living around that time.  That all modern males are descended from him suggested some kind of evolutionary “bottleneck” at that time, through which only a very small, related group’s were fit, in the Darwinian sense, to pass.  Maybe some other mutations conferred that fitness.  Perhaps some universal calamity reduced human population to only one or two small bands; chance rather than genetic determinism..  The third suggestion was that a small group’s development of a new technology conferred the potential for them to have progeny that survived to breed successfully for generation after generation, thereby coming to dominate the small populations of the pre-agricultural period.  The last would have had little to do with Darwinism, arising from a cultural change that had a dramatic effect.  The Genghis-related Y-chromosome discovery raises another possibility, that of social and sexual dominance of some “Big Man” through political achievement and ruthlessness; aspects of conscious social being and culture, and indeed economics and technology.  Tool makers and users who passed their skills down the generations are quintessentially human, and have increasingly developed with a cultural “cushion” from purely unconscious, natural processes for 2.5 million years.  Surely, some kind of “Big Man” (and possibly “Big Woman”) hypothesis has a place in thinking about human evolution as a whole.

The recent publications that described extremely old primate remains (Orrorin and Sahelanthropus), which may be early beings on the tortuous road to the emergence of humans, has set the circle of palaeoanthropologists abuzz (see A considered view November 2002 Earth Pages News).  Sooner or later, Scientific American was bound to commission an article in plain words that expressed all the conflicting views and  illustrated them magnificently, and so it has (Wond, K. 2003.  An ancestor to call our own.  Scientific American, January 2003, p. 42-51).

Earth Pages News has a bias towards investigations of human origins, simply because it is that branch of the geosciences with the most immediate bearing on our readers.  Much of the reported material has been technical.  So, it is pleasing to direct readers to a profile of a palaeoanthropologist who is not a self-publicising diva (Gibbons, A. 2002.  One scientist’s quest for the origin of our species.  Science, v. 298, p. 1708-1711).  Michel Brunet, of the University of Poitiers in France has spent his professional life researching Neogene mammals in as many likely sites to which he and his colleagues could gain access.  It has been a risky business, and at least one of his close colleagues died in the field, and Brunet has had many close encounters with acute danger.  Late in his career he hit the bonanza represented by Sahelanthropus tchadensis  (see Bonanza time for Bonzo, August 2002 Earth Pages News).  Not only did the find take his team far beyond the time frame of previous signs of hominid evolution, but completely outside the usual hunting grounds of eastern Africa to Chad.  That hominids were not exclusive to the area of the East African Rifts had already been demonstrated by Brunet and  David Pilbeam of Harvard by their find of 3.5 Ma australopithecine remains there in 1995.  Time will tell if this seemingly quiet academic is turned into yet another diva by the media circus that inevitably scrums around palaeoanthropologists with big finds.  I reckon he will remain as he is.

Assessing relatedness in the male line from Y chromosome samples of large, widespread populations, is becoming an important tool in palaeoanthropology.  It uniquely shows signs of the major migrations by fully modern humans during the last glacial period and the Holocene (see Eve never met Adam December 2000 Earth Pages News and  Multiregionalists nailed by Y chromosome? June 2001 Earth Pages News).  Although the details make difficult reading for non-geneticists, a recent paper by a large multinational team, led by Spencer Wells, Ruslan Ruzibakiev and Nadira Yuldasheva of Oxford University and the Uzbekistan Academy of Science respectively, sheds important light on where these migrants set out from (Wells, R.S. and 25 others 2002.  The Eurasian heartland: A continental perspective on Y-chromosome diversity.  Proceedings of the National Academy of Science, v. 98, p. 10244-10249).  Central Asian men have among the most diverse genetic make up of any living humans.  Genetic markers on Y chromosomes from that population turn up far afield, so that it seems that the great migrations to Europe, to the Indian sub-continent and even North America set out from the region of Afghanistan, Uzbekistan and Pakistan.

Is evolution predisposed to intelligent beings?

Simon Conway Morris of Cambridge University is one of the younger pioneers of palaeobiology, beginning with his doctoral studies of the famous Cambrian creatures of the Burgess Shale.  His discoveries and analyses of them have clearly set him on course for thoughts of a much broader kind, much as did the career of Stephen Jay Gould.  By way of introduction to his forthcoming book (Life’s Solution: Inevitable Humans in a Lonely Universe, Cambridge University Press, scheduled for 2003) a recent article by him (Conway Morris, S. 2002.  We were meant to be….  New Scientist, 16 November 2002, p. 26-29) will cause a stir.  At first sight it smacks of teleology, the predestination of biological processes to create the thinking mind.  It is far from being teleological, because Conway Morris argues from sound evolutionary principles about the role of fitness.  To him, there is evidence of evolutionary convergence towards smart creatures, such as dolphins and even octopuses and social insects; the outcome of gathering and processing information in some kind of integrated mental map.  Unfortunately, detecting signs of such behaviour in the fossil record is not easy, unless advanced intelligence created recognisable artefacts.  Such evidence spans only the last 2.5 Ma, and of course it originated with hominids, and with them alone; we find few signs of the dolphin’s predilection for using snout guards while grubbing in the seabed – a likely tale!.  What he does not address is the difference between intelligence and the consciousness that turns environments into tools for our species, which in turn drive the generation of culture, economy and a free association of individuals.  Much as we might wish to, we cannot converse with a dolphin, an advanced mollusc or an ant.  Which is a shame, because a really smart cookie needs to work on the principle of, “It takes one to know one”!  All manner of living animals use tools of a rudimentary kind, even the song thrush in my back yard, so Conway Morris is mainly restating a truism.  But that is fine as a starting point for speculation, and what I take to be pure fun.  But as a basis for some optimism that when we meet a truly alien intelligence it should be pretty easy to have a good old natter, is being silly.  If he does hold that view, then I can recommend a few hours in the Aztec exhibition in London; as like as not we would be a menu item for any intelligent being which had crossed a thousand light years out of curiosity or for plunder!  Life’s history on Earth has not been simply one of evolution, but of awesome snuffings out, and many other chance combinations of circumstances outwith any kind of biological necessity.  Being ever so clever is little help against a Chixculub or the Siberian Trap.

Find after find of hominid remains (Bonanza time for Bonzo – August 2002) undoubtedly forces physical anthropologists to reflect on what their still tiny collections of fossils might signify about the descent of humans.  There are two ways of looking at that; as a “tidy” tree and one that is essentially “untidy”.  The first seeks a means of connecting the earliest remains to later ones by the simplest possible connections – a touch of Occam’s Razor.  However, more diversity and ever increasing ranges of ages and localities for the remains inevitably challenges this kind of palaeontological “good housekeeping”.   Bernard Wood of George Washington University has long regarded evolution as untidy, and the finds of Sahelanthropus tchadensis and Orrorin tugenensis, around 6 to 7 Ma old, reinforce his trenchant views (Wood, B. 2002.  Who are we?  New Scientist, 26 October 2002, p. 44-47).

Because the genetic similarity between humans and their nearest relatives, chimpanzees, seems to suggest that the two clades diverged between 5 and 10 Ma ago, Sahelanthropus and Orrorin may be pretty close in age to that division.  But what were they?  Wood’s view is interesting, and a worry to the advocates of a parsimonious set of connections.  Connectivity in proposed clades rests, for obvious reasons, on purely physical characteristics.  There are many examples from the fossil record of animals whose outwardly similar characters, for example those shared by sharks and dolphins, do not signify inheritance from common ancestry.  This is homoplasy, and raises the awkward possibility that special characters, regarded as essentially human, need not have arisen only the once and been carried by linear descendants.  The often quoted “golden characters” of big brains and upright gait, that confer an opportunity to develop consciousness through freeing of the hands, may well have arisen more than once.  The truly odd thing about Sahelanthropus is just how “modern” its face looks.  Beetling brows, thick jaw and un-apelike canine teeth would put it on a sort of par with fossils of species of Homo that arose 4 to 5 million years later.  Yet none of the fossils in between have this combination.; in the “tidy” scheme of things they are more “primitive”, and “therefore” cannot be our ancestors.  Quite a muddle! Faces, the most sought after bits of bone, isolated in time and place could well have led many up the proverbial garden path.  Why, suggests Wood, shouldn’t early hominids have been dead ends morphologically, with “primitive” characters making repeated comebacks?  Why, too, shouldn’t they have been ancestral chimps, or even neither chimp nor human?  The dearth of late-Miocene and Pliocene non-hominid fossils of primates leaves all this as possible.  He reckons the search for “missing links” has always been a non-starter.  Whatever, by expanding enormously the area of potentially fruitful ground from the narrow confines of the East African Rift, the Sahelanthropus find in Chad may yet lead to a big increase in the number of hominid and other primate fossils over which physical anthropologists can ponder.

Some years back, a near complete skeleton emerged from a terrace on the Columbia River, in the north-western USA, near to Kennewick.  Preliminary examination suggested that the skull had distinct European features, and some thought that these were the remains of some early pioneer.  Kennewick Man attracted considerable attention when the terrace was dated at 9300 years, because the individual would then have been among the earliest known colonizers of the Americas.  Five local tribes of  Native Americans laid claim to the bones under the Native American Graves Protection and Repatriation Act, considering him to be an ancestor.  The bones were taken into custody, thereby halting further research.  Several academics saw this in a malevolent light, since if it was proven that the skeleton was indeed of European origin instead of Asian that would undermine a major plank in Native Americans’ claims for primary occupation of land; the central issue in a vast raft of legislation over ownership of mineral reserves.  Pressure for release of the bones for research has built over the last two years, finally to overcome concerted opposition that wished to re-bury the bones with due resepct.  The magistrate who judged the case found the original decision for sequestration “arbitrary and capricious”, and so investigations can resume.  Quite possibly DNA will be preserved, and that could set the cat among the pigeons in Native American circles.  However, some experts who had a quick look at the skull suggested that it might well be of an Ainu, one of the earliest inhabitants of the Japanese islands, who bear passing resemblance to Caucasian people..

Finding a new species of fossil organism is not usually a big deal.  There are lots out there, and palaeontological journals publish formal descriptions regularly.  The finder moves on, and as often as not allows other scientists in the field free access to the original specimens.  Free exchange of published data, allowing colleagues to add to knowledge of materials by direct study, and, in most branches of science, verification by inter-laboratory analysis of material is part and parcel of research.  The priceless Apollo lunar samples and many meteorites move freely because of these informal protocols.  Things are different when the materials are “hot news”, none more so than remains from the human bush of evolution (Gibbons, A. 2002.  Glasnost for hominids: seeking access to fossils.  Science, v. 297, p.1464-1468).

Protocols for hominid specimens often allow access only to the finders, their colleagues and trusted friends, until they have performed the most minute investigation and written detailed monographs.  The rules are sometimes laid down legally at governmental level.  This can extend even to casts and CT-scan facsimiles. There are often delays of a decade between first publication of a new species and basic information, and the fossils’ entering the public domain.  Unsurprisingly, this frustrates palaeoanthropologists who do not have the luck to make a major discovery – useful hominid material is exceptionally rare, despite the fanfares which greet its first publication.  Consequently, eager students of human origins try various ploys to get in on the act, such as detailed photography of specimens in museums, and furtive digs for new material at the original sites.  Sometimes they are thwarted, sometimes not (See April Earth Pages News, Homo erectus unification?).  Berhane Asfaw, of the Middle Awash Research Team that has done so much to advance knowledge of our early ancestors, commented, “You don’t know how we suffered in the field to get these fossils”, when putting a halt to such a disingenuous attempt to snaffle pictures.

The big news of July was without doubt from the palaeoanthropologists; a report on finds at the 1.75 Ma Dmanisi site in Georgia (Vekua, A. and 11 others 2002.  A new skull from Dmanisi, Georgia.  Science, v. 297, p. 85-89.), and the unveiling of a hominid-like skull from Chad dated at 7 Ma (Brunet, M. and 37 others 2002.  A new hominid from the Upper Miocene of Chad, central Africa.  Nature, v.  4418, p. 145-151).  Both threw the issues of human origins, evolution and migration back into the arena of debate.

Time and Newsweek, and once upon a time Life magazine often figure celebrities of the week or month on their covers.  Nature entered the celebrity cult on 11 July with a front-page photo of the magnificent cranium of Sahelanthropus tchadensis’ holotype found and analysed by a vast team from France, Chad, USA, Switzerland and Spain.  The skull is from Upper Miocene sediments around Lake Chad, dated from their varied fauna which is very like that of similar sediments in Kenya.  Its hominid credentials stem from the skull’s face, jaw and teeth, but it is odd.  From the back, it resembles a chimp, and so does the capacity of its brain case.  From the front, it bears close resemblance to an advanced Australopithecine.  Yet no limb bones have been recovered so far, and the attachment point of the skull to its backbone is not mentioned.  Both features would be needed to prove upright gait.  Undeterred, the authors and many commentators are convinced that it is the oldest human ancestor, from the very limit in time at which modern genetic analyses suggest that the human “bush” of descent parted from that which led to modern chimpanzees.  Bernard Wood of George Washington University (Wood, B. 2002.  Hominid revelations from Chad.  Nature, v.  418, p. 133-135) discusses Sahelanthropus’ significance to human evolution, implying that it poses problems for both the linear model of descent from a single emergence of basic human anatomy and the “untidy” model, to which he subscribes – adaptive radiation to changed circumstances that occurred more than once.  In the “untidy” model, even an excellent-looking candidate for the first in the line may not have been ancestral to us.

Palaeoanthropologists have never been as well-endowed with bones as they are with funds, and one detects hints of the protectiveness that has long plagued the discipline.  The finders of the previous candidate for the first hominid – Brigite Senut and Michael Pickford of the Natural History Museum in Paris (Taking stock of hominid evolution, Earth Pages News, March 2002) who found Orrorin tugenensis, in 5.72 to 5.88 Ma sediments of the Tugen Hills in the Kenyan Rift – claim that Sahelanthropus is merely an ancestral gorilla, citing the creature’s large canines.  Without a pelvis or footbones to back up the hominid claim, they could well be right.  However, the good news is that East Africa has lost its primacy as the source of fossils bearing on human evolution.  Being 1500 km west of the nearest previous site, and unrelated to the East African Rift system.  The new sites in Chad open up a vast area for future searches of potentially fruitful Miocene sediments, that are neither abundant nor complete in the Rift (its formation is post-Miocene).

Georgia in the former Soviet Union has grown in significance since the first reports of very old human remains near Dmanisi, a decade ago.  The site is well preserved, contains abundant mammalian remains, and the containing strata overlie a 1.85 Ma basalt.  With supplementary palaeomagnetic stratigraphy, Abesalom Vekua and his colleagues from several Georgian institutions, the USA, Spain and Switzerland have narrowed the age of the site to 1.75 Ma.  Their new find is a superbly preserved  skull, together with a lower jaw, following earlier discoveries of two other cranial fossils.  The site is well endowed with stone artefacts, similar to those of the Oldowan culture of East Africa. 

The new skull has a smaller brain capacity than co-eval H. ergaster or H. erectus in Africa, and bears some resemblance to the earliest species of human, H. habilis, although the authors prefer not to muddy the waters with yet another species of Homo.  However, had this skull been found first, they might well have gone for H. habilis, and in the paper suggest that it and the others may have descended from habilines that left Africa some time before they were preserved.  As with Sahelanthropus, no limb bones have been found at Dmansi so far.  The three fossils are not identical, and another important possibility is that these humans, like us, were polymorphic, though this needs to be tempered with the possibility of differences between males and females, or that the smallest may have been adolescent.  Others have jumped on the differences to suggest that more than one species are represented.  Here we see the problem of meagre evidence, so that anatomy alone permits either “lumping” or “splitting”.  Jonathan Kingdon, in his book Self made man and his undoing (1993, Simon and Schuster) raised the issue of polymorphism, so characteristic of modern humans, to the consternation of most palaeoanthropologists, who remain largely silent on its implications for the whole issue of human classification.

There is no doubt that early humans with primitive tools were able to expand out of Africa as early as 1.75 Ma ago.  They were not well-endowed with brain power, and they were little people – they did not stride purposefully into the wide, blue yonder.  That they reached Georgia, of all places, is extremely odd, because a direct route from Africa is barred by the Caucasus mountain range, and the deserts of Syria and Iraq.  They might have tramped around the coast of Asia Minor, following the Dardanelles to the Black Sea coast and then into the Georgian plains.  A more extreme possibility is that first they crossed the Straits of Bab el Mandab (closed at the time) and, in Kingdon’s words, “standloped” to east Asia and the backtracked along the northern flanks of the great mountains of Asia to reach the steppes.  Finds of Oldowan artefacts and meagre human remains in China also provide ages around 1.8 Ma.

Ethoarchaeology attempts to use observation or experimental approaches to animal behaviour to shed light on  features of fossil occurrences that relate to human origin.  One example is examining the gnaw marks on bones in the dens of predators to check if they match similar signs on the bones of early hominids.  Another is knapping flints to see if the flakes or debris produced match finds of broken fragments at sites with no clear sign of early-human involvement.  Chimps use lumps of stone to break nuts on wooden anvils, and so provide natural subjects to probe what early hominids may have been up to.  Anthropologists from George Washington University in the USA and the Max Planck Institute for Evolutionary Anthropology in Germany have painstakingly excavated the debris from a nut-cracking site beneath a large tree “traditionally” used as a source of nut protein by Ivory Coast chimps (Mercader, J. et al. 2002.  Excavation of a chimpanzee stone tool site in the African rainforest.  Science, v. 296, p. 1542-1455).

Broken fragments inadvertently created by the chimpanzee troupe do resemble the earliest Oldowan tools, which appear in the fossil record at around 2.5 Ma.  The chimps can be shown to have brought hammer stones from several rock outcrops.  However, any old rock serves their purpose and there is no sign of deliberate selection, unlike the makers of Oldowan tools, who clearly selected rocks that break to give sharp edges from outcrops up to several kilometres from the fossil sites.  The first Oldowan tools demonstrate that they are the end product of what was probably a progression from accidental stone breakage.  The way in which broken fragments from patterns around chimps favourite anvils for nut cracking should help identify earlier assemblages in the steps towards proper tool making.  With luck, they may relate to fossils of the actual beings who were involved.  The 2.5 Ma Oldowan tools from Ethiopia have yet to be linked to a hominid species.  The earliest direct link between tools and their makers is the association of Oldowan artefacts with remains of Homo habilis about 2 Ma ago.

It is difficult to resolve the “multiregional” versus “out-of-Africa” debate about the origin of modern humans on the basis of fossil evidence.  For some time, it has seemed that there were fundamental anatomical differences between earliest members of the genus Homo in Africa and those found in Asia.  The 19^th century discovery by Dubois of what he called Pithecanthropus erectus ( now H. erectus) in Indonesia, set the taxonomic framework for recognising that species before early-human remains of similar antiquity (dating from about 1.8 Ma) were found in Africa.  At first regarded as H. erectus, the anatomical peculiarities of the early African remains eventually forced their reclassification as a different, perhaps ancestral species to “true erects” – H. ergaster (“Action Man”).  The fragmentary remains of the earliest Asian hominids do seem to be of this species, as do those dating to 1.6 Ma from Dmanisi in Georgia.  The lack of African fossils from the period up to about 600 ka permitted the view that H. erectus was an exclusively Asian descendant from early migrants; i.e. that there was a species divergence between Africa and Asia.  Two recent finds have cast doubt on that.

The first was of a well-preserved cranium, with associated tools and abundant mammalian remains, from the Danakil area of Eritrea (Abbate et al. 1998.  A one-million-year-old Homo cranium from the Danakil (Afar) Depression of Eritrea.  Nature, v.  393, p. 458-460), which seems to blend features of both H. erectus and H. sapiens.  The latest is claimed to be indisputably an H. erectus, and comes from the highly productive Middle Awash sediments of southern Afar in Ethiopia (Asfaw, B. et al. 2002.  Remains of Homo erectus from Bouri, Middle Awash, Ethiopia.  Nature, v. 416, p. 317-320).  The last also comes from the period around 1 Ma ago.  Such is its resemblance to Asian fossils, that there seems little point in considering any minor differences as being other than the results of the polymorphism which is so characteristic of modern humans (a view long held by the palaeoecologist, Jonathan Kingdon).  The authors also suggest that assigning earlier fossils to H. ergaster is neither necessary nor useful, for the African record now suggests that they are the early members of a lineage towards later “erects”.  The close resemblance between African and Asian “erects” does appear to indicate either repeated migration to Asia or continuous genetic contact between the two populations.

(Note  Acrimony that has no bearing on scientific debate flared up around the potentially revealing Eritrean, middle-Pleistocene sites at the annual meeting of the Palaeoanthropological Society in Denver (March 2002).  One of the members of the  University of Florence team, who discovered the site at Buia in Danakil, reported that on a recent visit local people had begun offering tools and fossils for sale.  Allegedly, the locals said they had been offered money by another team, possibly led by Randall Susman of the State University of New York.  Susman and co-workers strenuously deny offering bounties, yet have had their permit for future work withdrawn by Eritrean authorities (Dalton, R.  2002.  Hints of bone bounties rile fossil hunters.  Nature, v.  416, p. 356).  It seems hardly surprising that perceptive locals, who wrest a meagre living in one of the world’s most inhospitable places, seek to make their lives a little easier by selling what is clearly valuable enough to attract well-heeled scientists to their homeland.  Rather than allow innuendo to fog the scientific issues, it would seem wise to train people who know the area intimately to become skilled fossil hunters, and to pay them a decent wage, much as has happened in Kenya and Tanzania.)

Phyllogeography and “Out of Africa”

While 2001 was becoming the “Year of the Genome”, work continued unnoticed by the press on the growing amount of information about genetic differences between modern people in widely separated parts of the world.  Moreover, computer software developed to give more meaning to that geographic variation; the science of phyllogeography  emerged.  Analysis of genetic data, using sophisticated statistics, potentially reveals the different mutations that have appeared in widely separated populations over time, and also the degree to which genetic information entered such populations as a result of movement into them by people from far-off places.  It is a complex business, but may help resolve or reconcile the two main hypotheses about the origins of modern humans. 

The “out-of-Africa” hypothesis – launched by early work on modern humans’ genetic patterns – starts with the migration of Homo erectus from Africa to colonise Eurasia, perhaps as early as 1.8 Ma ago, thereafter to evolve separately in isolation from early Africans and perhaps one another.  Fully modern humans evolved in Africa and expanded again since about 100 ka to replace and genetically extinguish those older, non-modern populations.  The alternative view of multiregional evolution also accepts an African origin for H. erectus and its early migration outwards, but that it was followed by many genetic contacts of regional populations with Africa through continued migrations over the last 1.8 Ma.  That would allow local populations to differentiate because of the distances between them, yet gene flow between them and Africa would have maintained a single evolutionary lineage.  The many shifts in climate and sea-levels through the Pleistocene would have posed repeated stresses and opportunities for the regular migrations that this multiregional trellis model demands, hence the tenacity with which its supporters hold that view.  However, a notion of modern human populations having evolved in semi-isolation over such a long time carries inevitable connotations that many people find disagreeable.  There are political undertones in the debate that do cloud the scientific issues.

One of the supporters of the multi-regional model, Alan Templeton of Washington University, Missouri USA, has applied new statistical analyses to genetic data from mitochondrial DNA – first claimed as support for the “out-of-Africa” hypothesis – Y-chromosomes and 8 other sources of genetic information (Templeton, A.R. 2002.  Out of Africa again and again.  Nature, v. 416, p. 45-51).  His work confirms the ultimate African origin of all of us, but raises the possibility of at least two expansions out of Africa, at 600 ka and 95 ka.  Now that may seem to bring much needed support to multi-regionalism, but “again and again” is not the same as the many connections required by the hypothesis.  It is a powerful demonstration of how much remains to be done, put in context by one reviewer’s comment that genetic information from 35 individuals on a Pacific island, colonised in only the last 1000 years, is inadequate to say where all the genes came from (Cann, R.L. 2002.  Tangled genetic routes.  Nature, v. 416, p. 32-33).  In the global data used by Templeton to examine more than a million years of evolution, the groupings rely on samples from as few as 35 living individuals.

The dearth of fossils along humanity’s early evolutionary path inevitably results in even a single find forcing a rethink of the whole story.  Sometimes it exposes a novel characteristic, or a new date of occurrence, and quite minor deviations in relative durations of different species or minuscule differences in dentition or foot bones assume an importance that would be disproportionate in any other vertebrate group.  The last 2 to 3 years have unearthed evidence for the presence of bipedalism as early as 6 Ma ago, and three new primate divisions that seem on the line to humans rather than other living apes.  The 15 February issue of Science devotes 8 pages of News Focus to reviewing hominid evolution (Balter, M. and Gibbons, A. 2002.  Becoming human.  Science, v. 295, p. 1214-1225).

One picture that emerged more than a decade ago is that the richest pickings occur along the line of the East African Rift system, where continued extension since Miocene times has created room for the deposition of terrestrial sediments and thus chances of preservation.  Moreover, its continual volcanic activity has interleaved sedimentary strata with lava flows and ash beds that present ample opportunities for precise dating.  It is in the Rift that the onset of human-like traits has been pushed further and further back in time.  The discovery of Ardepithecus ramidus (“root Earth-ape) at Aramis in the Afar province of Ethiopia by The Middle Awash Research Team in 1992 (dated at around 4.4 Ma) pushed “Lucy” and the earlier, but fragmentary 4 Ma Australopithecus anamensis out of specialists’ ranking as the first in our line.  Last year Yohannes Haile Selassie published details of an earlier Ardepthicus subspecies from Afar, whose age is between 5.2 to 5.8 Ma.  In both, the central evidence for being hominid rests on foot bones, for the teeth bear a mixture of chimp- and human-like features.  Ardepithecines possibly could walk bipedally, but probably ate soft fruit and leaves in forested hills.  And then there is Orrorin tugenensis (“original man”) from the Tugen Hills in the Kenyan Rift, coming in at 5.72 to 5.88 Ma.  This so-called “Millennium Man”, found by a joint French-Kenyan team.  Its gait has still to rest on what to most of us might seem like flimsy evidence, modelled from three thighbones.  Orrorin’s teeth have mixed human- and chimp-like characters.  Unsurprisingly, Orrorin’s finders claim primacy as well as a nice new name, while those responsible for slightly younger Ardepithecus argue that both are the same genus.  The most important point, assuming that bipedality can be convincingly demonstrated for both, is that neither dwelt in grasslands, but in forests.  Bipedality might not have evolved through pressures that emerged with the spread of African savannah.  Although yet to be published, and dated only by stratigraphic means, an early forest dwelling hominid fossil, found last year in northern Chad by the French-Chadian Palaeoanthropological Mission breaks the stranglehold of the Rift on exploration for early hominids.  Two thousand kilometres from the Rift, the Chadian find implies that hominids roamed over a vast tract of a largely flat continental surface.

As well as a flurry of revisions to the human evolutionary “bush” (and each anthro to their own!), the oldest date comes dangerously close to the 5 to 7 Ma date of last common ancestor between the chimp and the human lines, as estimated from the difference between modern DNA sequences.  One among several possibilities is that the chimp human separation involved acceleration of evolution in our line; something often attributed to a “bottleneck” when numbers of individuals dropped to such a low level that mutations spread rapidly, instead of being “ironed out” in a larger gene pool.  There is one worrying aspect of the hunt for human ancestral fossils – there seems to be little parallel effort to seek early chimp fossils, or at least they are exceedingly rare.  That may be because true tropical rain forest with its highly oxidizing soils destroys the evidence.  Whatever, there is a possibility that among the increasing number of supposedly hominid fossils could be some ancestral chimpanzees!  All that would be required is a reversion to knuckle walking in forest environments.  Bone and tooth enamel cannot resolve that possibility.  The only possible way forward is more finds in a wider geographic diversity of sites, which the finds in Chad suggest is achievable, given Miocene to Pleistocene successions.

The thrust of research shifts from bones to artefacts in the case of Homo species, and how they might be interpreted in terms of cognitive ability.  Most important are signs of  abstraction from the natural world; in a word, art.  There has long been a Eurocentric bias, largely because of the wealth of exquisite objects that explode into the archaeological record there after 40 thousand years ago.  Art is a sure sign of fully human cognitive abilities, no matter how much physical anthropologists might ponder over this or that feature of skulls from the late-Pleistocene, and its role in shaping brain architecture and function.  Sudden European appearance of artistic expression has long spurred the view that its evolution was explosive and unique, probably as a result of some mutation.  That view needed revision as soon as Christopher Hinshilwood of the South African Museum reported his find in January this year of geometrically carved ochre objects close to Cape Town.  They are 77 thousand years old, but are not exactly prancing horses.  More common are tools, and major advances seem to have taken place in Africa, long before they appear in Europe at around the same time as artistic impressions.  Photographs of the engraved ochre objects bear strong resemblance to recent “doodles” by hunter gatherers and even runestones or tally sticks.  It is certainly a case of “Who knows?”, until more finds come to light.

Unsurprisingly, palaeoanthropologists pay a great deal of attention to teeth and have friendly relations with dentists. The tendency of our ancestors’ remains to be gnawed and otherwise dismembered left more of them around than other skeletal bits and pieces.  Based on the old adage that we are what we eat, teeth reveal a great deal about hominin habits.  They also take up trace elements from the environment in which individuals lived at an early age, thereby giving hints to migration.  Astonishingly, tooth enamel grows day by day, and tooth development can be charted with great precision.  Together with the timing at which different teeth erupt in juveniles, fossil dental records potentially allow researchers to detect when in human evolution the unusually extended childhood of humans first appeared, and whether it developed gradually or suddenly.  The particular focus is on teeth from prematurely deceased hominins. 

Modern humans’ rates of enamel growth is much slower than that in apes.  Despite the many signs of a profound physiological differentiation between apes, australopithecines and early species of Homo, as far as tooth growth goes, they are all similar (Dean, C. et al. 2001.  Growth processes in teeth distinguish modern humans from Homo erectus and earlier hominins.  Nature, v. 414., p. 628-631).  The teeth of each grew faster than in modern humans.  In dentition at least, there is little sign of an advance in childhood development even in anatomically very modern-looking H. erectus.  That must have taken place in early modern humans, and needs to be checked in them and our co-descendants, the Neanderthals.

Teeth provide by no means the whole story.  The near-complete skeleton of the famous Turkana Boy provides lines to suggest that when he died, his growth was well within the range of modern human development (Moggi-Cecchi, J. 2001.  Questions of growth.  Nature, v. 414, p. 595-596).  It seems unwise to rely entirely on teeth.  One possibility is that several important features (brain size, growth of tooth enamel, and even bipedalism) may have undergone repeated evolution – two steps forward, one step back?