The article is very interesting and informative, and comes from a good source. But I have to quibble about describing Denisovan and Neandertal hominins who were ancestors of current human beings as coming from a "different species," because by one of the main concepts of speciation, if two organisms can mate and have viable offspring, and then the offspring can further reproduce, you say the two organisms are part of the SAME species. There are, of course, full-length books about the details of defining species among the common descendants of the earliest living things, and about the mechanisms that bring about speciation among the descendants of a common ancestor species,[1] but right now we don't always know for sure when we dig up old hominin bones which belong to relatives of direct ancestors of living human beings and which do not--that is part of what the studies of ancient DNA are intended to find out.<p>To make the point I am bringing up here, I would rewrite the second sentence of the helpful article kindly submitted here to read, "As the individuals who provided the main genetic contribution to modern humans began to spread out of Africa roughly 50,000 years ago, they encountered other hominin clades that looked remarkably like them — the Neanderthals and Denisovans, two groups of archaic humans that shared an ancestor with us roughly 600,000 years earlier."<p>[1] <a href="http://www.amazon.com/s/ref=nb_sb_noss_2?url=search-alias%3Daps&field-keywords=Speciation" rel="nofollow">http://www.amazon.com/s/ref=nb_sb_noss_2?url=search-alias%3D...</a>
Based on prior discussions I've had the impression that the BNC2 and other skin-related Neanderthal genes were associated with less melanin pigmentation.<p>Melanin reduces penetration of UVB into skin cells, important in an equatorial environment to protect skin integrity. However in northerly latitudes, heavily pigmented skin is a disadvantage due to the role of UVB exposure in producing vitamin D, essential to survival.<p>Indeed the most pigmented skin requires 5 times the UVB exposure to produce equivalent amount of vitamin D vs. least pigmented. A possible tradeoff for adaptating to an environment with less available sunlight is greater susceptibility to developing conditions like melanoma, but that's admittedly an oversimplification of a very complex subject.
The world map for Denosovian DNA is wrong. The Australian/Papua population is around 6% not the 0.8% which the figure shows.<p>It is a shame that Africa is so ignored in these studies. We know that there were many interbreeding events that occurred in Africa (the African pygmies are one example), but we know almost nothing more.
The colored map is informative - color reflects percent of archaic genes inherited by modern populations. But the placement of the colored dots looks suspiciously like a heatmap. I know the data is sparse. But maybe there'd be a better way to represent it.
The genome percentages in the article are a bit confusing. It is oft-quoted that we are "99% Chimpanzee", so how could we also be no more than "6% Denisovan"? Answer: they really mean 6 percentage points "realigned" vs the African reference populations. I've read many other articles repeating the "6%" and it would be nice if they (and this) were clearer (and used the correct units--but maybe that's too much to ask).<p>Some cool charts for reference: <a href="http://www.scientificamerican.com/article/tiny-genetic-differences-between-humans-and-other-primates-pervade-the-genome/" rel="nofollow">http://www.scientificamerican.com/article/tiny-genetic-diffe...</a>