Young age for “Mungo Man”

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 13th 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.

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