By Peter Dearden 11/07/2015

The evolutionary history of the human species is complex, but hidden in that complexity are some remarkable things.

A few years ago geneticists sequenced the genome of what we thought were our closes relatives, the extinct Neanderthals. That is remarkable. In 2002 we completed the Human genome sequence; just a few years later (2010) we are sequencing the genomes of things that aren’t even alive anymore.

Those sequences came from bones preserved under flowstone deposits in caves, bones that had just enough DNA in them to be sequenced. A finger bone from a cave in the Altai Mountains, though to be a Neanderthal was also sequenced and turned out not to be from a Neanderthal at all, but from a previously unknown hominid, now know as a Denisovan. More research has led to the sequencing of the Denisovan genome, and an understanding that Denisovans lived in northern parts of Asia – a very extensive area.

What I found most unexpected about the sequence of Neanderthals was that some of their DNA variants are present in some humans. Humans that left Africa appear to have mated with Neanderthals and carry some Neanderthal variants of their genes. The evidence implies that this is also true of Denisovans. A smaller part of the family tree of humans carry Denisovan DNA, we seem to have mated with them too and carry some of their DNA variants. All very nice, but a paper last year has shown that not only do some individual carry Densiovan DNA, but also that that DNA actually allows to them to adapt, to cope better with, the environment they live in.

One of these adaptations is a strange variant of a gene called EPAS1(stupid name I know), which is a gene involved in responding to hypoxia. Now, follow me here. Hypoxia, a lack of oxygen, is a problem at high altitudes. Tibet is at high altitude. Tibetan people are well adapted to living at high altitudes. So, it is thought that this EPAS1 variant in the Tibetan population helps them cope with hypoxia. Yet, this strange variant of EPAS1 isn’t found in nearby populations, it isn’t found in Han Chinese, but it is found in the Denisovans. In fact the weird variant of EPAS1 only appears in all Denisovan DNA, and in Tibetans.

The conclusion is that this bit of DNA, which helps Tibetans cope with high altitude, comes from matings with Denisovans in distant human prehistory. Through mixing with them, we have picked up this useful bit of DNA, and now Tibetans use it to cope with their environment.

Understanding the complexities of our ancestry, by tracing where our genes come from, helps us better understand ourselves. That Denisovan finger bone, unexpectedly found in an out of the way cave, turns out to hold information that helps explain how we have been a success as a species.

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