Roger Hanson: Exploring the history and genetics of Neanderthals and us
Thursday, 5 October 2017
If you are not an indigenous sub-Saharan African then there are Neanderthals in your family tree.
Modern genetic studies are revealing how this happened.
A human-like species, Homo erectus, is thought to have evolved in East Africa about 3 million years ago. (The word Homo is a Latin noun meaning 'human being' or 'man', and is a biological classification which includes us as well as human-like species).
Two million years ago the first Homo erectus, began to migrate from East Africa and over the next 1.3 million years spread across a vast area from Georgia in Russia to Indonesia.
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Homo erectus disappeared about 70,000 years ago. Fossil finds reveal that about 700,000 years ago another human-like species, Homo heidelbergensis, evolved in East Africa. About 350,000 years later, some Homo heidelbergensis became the second human-like species to migrate from Africa.
Shortly after, they split into two groups, one group spread into west Asia and Europe and the second group spread into east Asia. A third group remained in Africa.
These three separate populations of Homo heidelbergensis, through the process of evolution, produced different Homo species.
The group that moved into west Asia and Europe eventually became Neanderthals.
Evolution over several thousand years changed the east Asian group into a different sub-species called Denisovans. The evidence for the Denisovan sub-species is sparse – just two teeth and a finger bone found in a cave in Siberia, but their DNA is different from Neanderthal DNA although, like Neanderthals, they definitely evolved from Homo heidelbergensis.
The group of Homo heidelbergensis which remained in Africa, over a period of about 200,000 years became Homo sapiens, our direct ancestors.
What happened next changed the evolution of life on Earth dramatically – a group, this time of Homo sapiens, migrated from Africa. About 60,000 years ago, most probably in the geographic bottleneck of the Levant region in the Middle East, Homo sapiens first encountered Neanderthals.
Scientists in the 1970s considered it unlikely that the two species interbred, however with the rapid advances in genetic science since the 70s, numerous studies have revealed that the two species did interbreed.
The offspring of this encounter acquired Neanderthal genes. Today, if you are not an indigenous sub-Saharan African, 1-4 per cent of your DNA is Neanderthal.
If you are an indigenous sub- Saharan African then your Homo sapiens ancestors never met the Neanderthals.
In Siberia, Homo sapiens interbred with Denisovans and their offspring headed further east and south.
Today, indigenous people from Vanuatu, New Guinea, the Solomon Islands, Fiji and aboriginal Australians have up to 6 per cent Denisovan genes in their DNA, that's in addition to the 1 to 4 per cent Neanderthal genes present.
A team of researchers from Washington State University reporting in the journal Science have identified as much as 20 per cent of the entire Neanderthal genome was present in the 665 people they tested.
In 2014 a National Geographic article reported that the protein keratin, found in skin, hair and nails is especially rich in Neanderthal DNA.
It has also been discovered that variants of Neanderthal genes present in some humans help protect against diseases such as lupus, Crohn's disease and type II diabetes.
These positive features of Neanderthal genes probably explain why they have remained in the gene pool.
Neanderthals were comparable in height with modern humans but much stronger. They were broader across the shoulders, barrel-chested, had a low, flat elongated skull with a prominent brow ridge and lacked a protruding chin.
Today we are the only surviving members of the Homo species. Neanderthals and Denisovans disappeared about 30,000 years ago.
It isn't entirely clear why these other groups became extinct. They were probably absorbed into the much bigger gene pool of modern humans or they could have lost out in the competition for resources by their smarter cousins or it could be that Homo sapiens killed Neanderthals.
There is something profound about the fact that much of the population of the world today have genes derived from a liaison between Neanderthal and Homo sapiens ancestors - a connection which can be traced back to an encounter in Euroasia tens of thousands of years ago, revealing much about how we came to be.