Modern humans started out in Africa. About 100,000 years or so ago, groups of these humans began leaving for the Middle East.
These groups then continued to spread across Europe, Asia and Australia and eventually to the Americas. But they weren't spreading into places without human relatives, just to places without humans.
See, groups of Homo erectus had left Africa around 1-2 million years before and settled the world. Each group evolved along a slightly different pathway depending on the local environment, chance, etc. One of these groups evolved into Neanderthals.
Scientists have been arguing about the history of the human race for a long time. One idea, called the Multiregional Model, argues that after Homo erectus left Africa, each group evolved separately into modern Africans, Asians, Europeans, etc. The second model, Out of Africa, argues that humans evolved in Africa and then wiped out the other groups. Most scientists today support the Out of Africa model.
As with a lot of science, reality is probably a bit more subtle than either of these extremes. In fact, reality is probably more like the Middle Ground model. What this model argues is that humans evolved in Africa but that there was some interbreeding between humans and the other species. This interbreeding is part of the reason for the different ethnic groups that are alive today.
Not much earlier research supported the Middle Ground model. Scientists looked at fossils and could find very little support. There was a Portuguese Neanderthal skeleton
that suggested interbreeding but it was just one fossil. And looks at mitochondrial
and Y DNA showed no evidence of interbreeding.
But of late, two key pieces of data have come out that support interbreeding. Back in April 2010, researchers looked at over 2000 different people's DNA
. When they analyzed the DNA, the best explanation they could come up with for what they saw was that humans and Neanderthals had interbred significantly twice. The first time was 60,000 years ago in the eastern Mediterranean and the second was about 45,000 years ago in eastern Asia.
The second piece of data is more direct than this and is the focus of this article. In this study, scientists directly compared Neanderthal DNA to human DNA and saw regions of Neanderthal DNA in European and Asian DNA. But they didn't see the reverse"Šthey didn't see human DNA in the Neanderthal DNA.
This means that humans and Neanderthal interbred but it was a one way street in terms of DNA. The Neanderthal DNA took hold in humans but not vice versa.
This kind of thing is possible if there is a colonizing group overtaking a settled area. Basically the humans had babies with the Neanderthals and these babies grew up and went on to colonize further into Neanderthal territory.
In these circumstances, the Neanderthal DNA in the human DNA would have a chance to settle in as half-Neanderthals had babies with other half Neanderthals. And these hybrids went on to dominate the colonization of Europe and Asia. The native Neanderthals died out before human DNA could take a hold.
So Europeans and Asians have a bit of Neanderthal in them. It'll be interesting to see if these regions have any advantage for the humans that have them. And maybe those Geico ads will have to be changed to, "So easy a European can do it."