Interbreeders

There's an anthropologist in St. Louis who used a computer simulation to prove that people interbred with other species for at least a million years. You know what that means -- Homo erectus is more ripe for punnage than ever. Washington University professor Alan R. Templeton published his findings in the recently issued Yearbook of Physical Anthropology, explaining that he'd finally disproved the popular "out of Africa" theory, which holds that Homo sapiens zoomed out of Africa roughly 100,000 years ago, killing every other hominid it met (including fellow tool users and fire makers Homo erectus and Homo neanderthalis).

Instead of killing, Templeton found, early humans were more likely having sex with these hominids on their way out of Africa into Asia and Europe. They also probably migrated out of Africa in three waves, rather than one or two, seeding Asia and Europe with early hominids who later cozied up with newly arrived groups.

Templeton figured all this out using a computer program called GEODIS, which reconstructs early human mating patterns by doing statistical analysis on population distributions of haplotypes, chunks of genes that get inherited together over long swaths of history. Based on what he found, Templeton says, "The hypothesis of no interbreeding is so grossly incompatible with the data that you can reject it."

It's always struck me as kind of weird that the dominant theory of human evolution -- often called the "replacement theory" or "single origin hypothesis" -- holds that Homo sapiens evolved all on its own in Africa, without any interbreeding with its comely hominid neighbors. The single origin hypothesis says that when Homo sapiens migrated out of Africa, it simply destroyed (or, in polite anthropology-speak, "replaced") all the other hominids. But even if we assume that Homo sapiens are such a bloodthirsty lot that their response to another form of intelligent life is to battle it, we all know what happens in battles. The conquered are often raped and/or enslaved. This seems like such a time-honored occurrence -- even inspiring a snotty little book by some prim profs a few years ago called A Natural History of Rape -- that it's hard to believe it wasn't happening in our earliest evolutionary incarnations.

Now you may be saying, sure, humans could have been raping Homo erectus, but that doesn't mean any of them made babies -- that's like saying humans who rape chimps are interbreeding. And you'd be right if it turned out to be true that there was only one migration out of Africa 100,000 years ago, when Homo sapiens had diverged enough from its fellow hominids that matings were likely to be sterile. But if Templeton's findings are accurate, there were migrations out of Africa 1.5 million years ago and 700,000 years ago, as well as the familiar one we all know and love, 100,000 years ago.

What Templeton's arguing is that the forebears of the creatures we are today -- Homo sapiens sapiens -- were interbreeding with the forebears of other hominid groups. His theory about the migrations at 700,000 years ago could help explain the sudden expansion in brain pan size among humans at that time, as well as evidence that tool use had begun to spring up among hominid groups across Europe and Asia. In Templeton's vision, we are hybrid hominids, not some pure species whose coolness and ingenuity allowed it to sweep over Asia and Europe "replacing" everything we found. We didn't "replace" other hominids; often, we merged with them.

Interestingly, Templeton sees his discoveries as a refutation of more than the replacement hypothesis. He sees it as scientific proof that racism has no rational basis. "You can be 99 percent confident that there was recurrent genetic interchange between African and Eurasian populations," he says. "So the idea of pure, distinct races in humans does not exist. We humans don't have a tree relationship, but rather a trellis. We're intertwined."