Excerpt from a National Geographic article (Jan 2014):
When modern
humans migrated out of Africa some 60,000 years ago, they found the Eurasian
continent already inhabited by brawny, big-browed Neanderthals. We
know that at least some encounters between the two kinds of human produced
offspring, because the genomes of people living outside Africa today are
composed of some 1 to 4 percent Neanderthal DNA.
We do not know this! I have a different suggestion: the genes picked up by humans from the Neanderthals some 40,000 to 100,000 years ago were not from interbreeding (vertical gene transfer). Instead they were picked up by horizontal gene transfer (or HGT). One plausible mechanism for HGT between hominids is viruses picking up and then dropping off pieces of DNA between individuals. Another is HGT between Humans and their microbiomes, HGT between Neanderthals and their microbiomes and then some sharing of microbiomes between Humans and Neanderthals.
Horizontal gene transfer has been suggested as the means by which several different primate species, which had diverged to become separate species over 100,000 years ago, all today have an identical DNA sequence (that provides a trait useful to survival) that had only appeared on the scene some 50,000 years ago (http://www.genomeweb.com/researchers-find-evidence-horizontal-gene-transfer-mammals-reptiles).
Sure, a news story is a lot more interesting to many when you conjure up the suggestion of inter-species sex. But let's not have sensationalism muck up that which would be our science.
More science around HGT:
http://phys.org/news/2013-11-virus-dna-neanderthal-genome-modern.html
http://www.biomedcentral.com/content/pdf/1471-2164-14-134.pdf
You can get 1 to 4 percent of DNA transfer through a viral mechanism?
ReplyDeleteI don't know. But I'd guess yes – given there is enough time for repeated transfers. I don't think that anyone has quantified the transfer rates in any species, let alone humans. Considering the span of time for overlap of modern man's ancestors living in the same regions with the Neanderthals (about 30,000 yrs estimated by some?) the rate would have had to have been on the order of 0.001% per generation. This does not seem outlandish. If the receiving group numbered 100,000 individuals, this could be 1000 individuals in the group (1/100) per generation each picking up .0000001%, or one individual per generation picking up .001%.
DeleteThis comment has been removed by the author.
ReplyDelete