Our Genetic Diversity

I found Razib Khan’s post on human genetic diversity fascinating. Here’s one of the key passages:

93-98.5% of the ancestry of humans outside of Sub-Saharan Africa (among those with no recent Sub-Saharan African ancestry, obviously) derives from a breeding population of 1,000 to 10,000, which expanded rapidly 60,000 years ago (reaching Australia and Europe around 45,000 and 50,000 years ago, accordingly).

So the simple “Out of Africa” narrative of a population crash and explosion across the world holds for North Africans, Eurasians, Oceanians, and Amerindians, some six and a half billion of us. But the origins of modern populations south of the Sahara are clearly more complex. Any bottleneck’s effects were much weaker within Africa, and multiple proto-modern populations seem to have been separating into distinct lineages as early as 200,000 years ago.

More graphically from a genetic standpoint Swedes and the Han Chinese resemble each other more closely than some people in neighboring villages in sub-Saharan Africa.

And speaking of graphics he includes some stunning graphics in his post. His map of migrations highlights and documents a point I have made here: as long ago as 15,000 years ago and almost certainly as long ago as 5,000 years ago human beings were just about everywhere in the world. No wonder the 16th and 17th century European explorers weren’t surprised to find people wherever they went. They were only surprised when they didn’t find people.

His post also ties in with another little news story, from the Associated Press:

WASHINGTON (AP) — What makes humans unique? Scientists have taken another step toward solving an enduring mystery with a new tool that may allow for more precise comparisons between the DNA of modern humans and that of our extinct ancestors.

Just 7% of our genome is uniquely shared with other humans, and not shared by other early ancestors, according to a study published Friday in the journal Science Advances.

“That’s a pretty small percentage,” said Nathan Schaefer, a University of California computational biologist and co-author of the new paper. “This kind of finding is why scientists are turning away from thinking that we humans are so vastly different from Neanderthals.”

The research draws upon DNA extracted from fossil remains of now-extinct Neanderthals and Denisovans dating back to around 40,000 or 50,000 years ago, as well as from 279 modern people from around the world.

all of which supports a point I’ve made here: the available evidence supports the hypothesis that present day human beings, Neanderthals, and Denisovans all belong to a single species. The relationship among us is more like the relationship among different breeds of dogs or horses than it is like a difference between species. What about Homo antecessor (800,000 ya) or erectus (1.7 million ya)? We may never know but I wouldn’t bet against all of us being members of the same species.