Category: Anthropology and Geoarchaeology

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

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

The oldest modern humans

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

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

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

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

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

A discovery that will run and run?

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

Something to chew over

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

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.