Aboriginal Genetics

13 Aug 2018

I've put this under archaeology as we don't have a genetics thread. It could equally come under anthropology - accept that we are dealing with the hard sciences (rather than the whimsical) - but see https://phys.org/print452844655.html ... A PNAS study (August 7th 2018) starts off with the premise, or so it would seem, that Aborigines arrived in Australia 50,000 years ago. Why do they do that as archaeologists have been pushing back the date of their arrival further and further back in time? It is all to do with genetics and this is a study by geneticists into the Aborigines. The archaeology is secondary - as far as concrete evidence is concerned (or in their opinion). The nub of the argument is what constitutes a modern human from a geneticists perception - and this is not to denigrate the findings but simply to inject a spot of healthy scepticism. The fact is that the idea Aborigines washed up in Australia was mainstream until recently - although some historians would have had it occur somewhat more recently. The key to the geneticist date is not archaeological however - it is the small percentage of what is perceived to be Neanderthal genes within Aborigines. One might wonder out loud if this should be Denisovan (which share Neanderthal genes I would have thought as they coexisted together) but no, the study defines modern humans as having a small proportion of Neanderthal genes (2.5%, which is negligible). THe defining date of this small Neanderthal input has been worked out via a process of genetic change over generations to 50,000 years ago - and the whole argument revolves around this calculation (which may be true or may be not). For example, if the small uptake of Neanderthal genes came as a result of a bottleneck one may wonder if a date of 40,000 years ago might be more appropriate. In that case one might argue have the authors been diplomatic, shall we say, by accepting a date of 50,000 years ago (as that was the mainstream archaeological view until not so long ago).

The authors also say the journey from Africa was long and arduous as they migrated across island in SE Asia. One is left wondering about their knowledge of disciplines outside genetics as Sunda Land existed up until 8000 years ago (the area west of the Wallace Line which was a single land mass but is now mostly submerged with island Indonesia the surviving upland zone). Of course we don't really know if Sunda Land existed 50,000 years ago - but there is a good chance it did. Also, we don't know the lie of the land between India and SE Asia at that time. The acceptance that the Aborigines were confronted by a succession of islands is just a poor assumption that has no merit. If the geoid of the Earth was subject to change, on occasion, their assumption might be completely awry.  The study raises some interesting ideas but who has the high ground - the geneticists or the archaeologists. Genetics is currently being presented by its practitioners as more of a hard science than archaeology - but is it. Is genetic change from generation to generation as solid as they say - or is it like sea level rise estimation (taking an exponential line when in fact it probably occurred in fits and starts). When C14 methodology first hit the scene they took the high ground too - until eventually shot down in flames as their results contradicted other C14 results and this was eventually rectified - after a long period of time and several critiques that involved the recognition that on occasion there were injections of C14 into the atmosphere (from elsewhere in the solar system) resulting in what is now known as plateua events. Does the use of genetics in archaeology have to undergo a bit more rigorous appraisal. 

To illustrate this piece of scepticism the authors of the study dispute the most recent archaeological dating of the Aboriginal presence - at around 65,000 years ago (which may suggest they were in Australia much earlier that that). This is done on the basis thatg the genetics is solid and the archaeological dating suspect - my discipline is more correct than yours, sort of thing. Why does the Neanderthal (or Denisovan) input have to occur 50,000 years ago - why not prior to that date? To understand this you have to read the full article.