The Neanderthal inside us

27 Aug 2012

Last week we had a paper saying that Neanderthal genes present in modern humans was due not to interbreeding but were a residue going back to before both species evolved, presumably Homo erectus and similar. Now, a pre-publication paper is reopening the debate - go to http://blogs.nature.com/2012/08/neanderthal-sex-debate-highlights-benefi... Scientists at Cambridge and Harvard have put their paper on the arXiv.org server but it originates from a specialist conference last year like the PNAS paper that was published last week. In other words, they are bot part of the dialogue going on in science and both are in response to an original paper by Paabo and Reich last year (or prhaps two years ago) who claimed they had discovered a small percentage of Neanderthal DNA in modern human populations of Europe and Asia - but not in Africans. The arXiv paper is based on a new method for determining when two populations interbred. It's bnased on the fact that our maternal and paternal chromosomes reshuffle after each generation. This mixing makes the contiguous chunks smaller with each generation and they concluded, from this process, that modern humans and Neanderthals interbred between 37 and 86,000 years ago, and probably or more likely to have mated between 47 and 65,000 years ago. Another paper with broadly similar conclusions is due out shortly but it could be stressed this is once again, research at the edge and it can change any time. One problem we might envisage is how modern humans came into contact with Neanderthals that long ago, and if it was not such a long time ago but at the lower end of the calculation, how might this impact on the calculated number of generations and how much Neanderthal is inside any of us. It is claimed the PNAS paper is now obsolete and yet it was only published a week or so ago. Finally, and most importantly, at the moment the whole argument is revolves around a single Neanderthal genome.

Going to http://johnhawks.net/weblog/reviews/neandertals/neandertal-dna/neanderta... we may note he too takes a swipe at the PNAS paper but for different reasons. His gripe is that it supports the Out of Africa consensus hypothesis and this is why it was written. He says it does not comply with the facts. Most palaeoanthropology, it seems, and we had all guessed that I suppose, is based on modelling as facts are in short supply - or have been until the genetics came along. Hawks is critical of the models, saying that we have lots of genetic data to compare with the Neanderthal genome and yet, the idea of Neanderthal ancestry has been challenged by several papers that have not performed any new comparisons at all. CVurrently, there is an unparallelled ability to explore the genome of humans and Neanderthals but we are aksed to believe a computer simulation that is fed no empirical information. Sounds a bit like climate science.

It emerges that the initial argument that there was only a 4 per cent survival of Neanderthal DNA in modern Europeans and Asians was itself a model based estimate, or calculation. It's funny how little details like that are not mentioned when research is presented in the media. Hawks says, how much Neanderthal ancestry is present in living people must depend on a more complex model of mixing among later populations.

Later, on page 4 of Hawks web post, he mentions the genome of Otzi the Iceman, the frozen remains found in a melting glacier in the Alps and dating from around 3000BC, when the global temperature appears to have suddenly tumbled. Otzi had a substantially larger degree of Neanderthal ancestry than living Europeans, it seems, which suggests that Upper Palaeolithic, and Mesolithic modern humans may have mixed with Neanderthals to a greater degree than other groups. It all implies there is a way to go before the Neanderthal in us all is finally squeezed out of the data (see also http://johnhawks.net/weblog/reviews/neandertals/neandertal-dna/1000-geno...