Author: zooks777

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.