How the story of human evolution continues to branch out

How the story of human evolution continues to branch out

Razib Khan writes:

Over the last 20 years, genomics, ancient DNA, and paleoanthropology have joined forces to completely overhaul our understanding of the origin of our species. The true diversity and complexity of human evolution over the last few hundred millennia surpasses even the most unhinged imaginings we might have hazarded just a short generation ago. But greater clarity has left us with a messier and less elegant narrative. Our species’ status, it turns out, is “complicated.”

In the year 2000, the orthodoxy was that humans spread across the world 60,000 years ago, and were descended exclusively from a small population in Africa. Neanderthals and various other human groups (and yes, we didn’t even deign to give them all names) were evolutionary “dead ends.” Of interest mostly to scholars, they were dismissed as failed experiments in a world our ancestors won. Today, this tidy story of us no longer passes a basic fact check.

In 2010, genomes recovered from ancient remains of “archaic hominins” in Eurasia turned out to have genetic matches in many modern humans. It seems they weren’t quite as “archaic” as we thought. In addition, we had to get used to the new reality that a solid 2 to 3 percent of the ancestry of all humans outside Africa is Neanderthal. About 5 percent of the ancestry of Melanesian groups, like the Papuans of New Guinea, actually comes from a previously unimagined new human lineage discovered in Denisova Cave, in Siberia of all places.

Since these first major overhauls, the genetic picture has only grown more complex. Trace, but detectable (0.2 percent or so), levels of “Denisovan” ancestry are found across South, Southeast, and East Asia (as well as among indigenous people of the Americas). Similarly, trace but detectable levels of Neanderthal ancestry actually appear in most African populations. And, though we have no ancient genomes to make the triumphant ID, a great deal of circumstantial DNA evidence indicates that many African groups harbor silent “archaic” lineages equivalent to Neanderthals and Denisovans. We call them “ghost” populations. We know they’re there in the genomes, but we have no fossils to identify them with. [Continue reading…]

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