[Apologies this one's up so very late. Busy day today.]
We’ve previously discussed the idea of lineage: that we can be assured that each one of our ancestors going back was able to pass on his and her genes, respectively, ultimately resulting in us. We tie these ancestors to a geographic location. My immediate lineage (myself included) come from the mid-Appalachians: present-day West Virginia. Go back a few hundred years and my ancestors all settle into two rough geographic locations: the British Isles and present-day Germany… ish. My mother’s paternal descent is Bavarian, we think, so that could be anywhere around southern Germany, Switzerland or Austria. The point is, I have a pretty good idea where these people all lived, and that probably holds up as far back as roughly a thousand years ago. Before that, though, who knows? Certainly my ancestors didn’t spring up in Europe all on their own; at some point they traveled there. Was it as late as during the era of the Roman Empire? Or was it as early as the first migrations of modern humans into Europe? I could send out samples of my DNA for analysis but all they’ll give me with present technology is a rough estimate and a bill for a few hundred dollars.
I get that with my car already.
One thing we do know, though, by combining fossil evidence with sequencing mitochondrial DNA from present-day humans and ancient remains is that all humans on the planet can eventually trace their lineages back to Africa, because that’s where all potential human ancestor species arose. But were those early ancestors modern Homo sapiens?
We previously talked about how there are three confirmed major migrations out of Africa, the most recent of which – roughly 100,000 – 50,000 years ago – was modern Homo sapiens. The idea that all present-day humans can trace their lineages to either those humans who migrated out or else their cousins who stayed put is, appropriately enough, known as the “Out of Africa” theory. Makes sense, right?
“But wait,” you say. “If there were three migrations out of Africa, and our ancestors were the third, then weren’t there already earlier human species spread throughout Eurasia when they got there?”
The answer is yes, there were, and we know that these modern humans interacted with Neanderthals at the very least.
You scratch your brow for a second and then slowly ask, “is ‘interacted with’ a euphamism for, uh…”
IT MIGHT HAVE HAPPENED.
Well, that’s not as silly of a question as you might think, because it turns out the answer very well might be “yes, it is.”
Yep, it seems that a team of scientists led by Jeffrey Long have found, by scanning the genes of a large number of people from across the globe, that many present-day humans who are not of pure African descent (eg, me) seem to carry some markers that are found in Neanderthals. This, they posit, is a telltale sign that there was enough human-on-Neanderthal action going on roughly 50,000 – 30,000 years ago (the peak period of interaction between humans and Neanderthals in Europe) that non-African present-day humans have some Neanderthal ancestry.
Of course, this is quite a thing, isn’t it? I mean, you could approach this from a metaphysical angle, an ethics angle… basically, you can chop it up and determine what it says about human nature as much as you like. For now, I’m only going to agree with Razib Khan when he says that it indicates that human ancestry is a lot more complicated than we thought not too long ago. That is, if this business [biznass?] with Neanderthals is true.
Genetics is a funny thing like that. It’s only one lens through which to examine the story of human ancestry. The use of genetics as a tool for a reductionist approach to figuring out our ancestry requires both a tremendous number of samples from present-day humans and solid samples from isolated times and places in the past. Still, it’s an act of trying to tease out a single, meaningful line connecting two points from a massive jumble that seems ever-more-complex with each time we get a better look at it. This is a prime example of what Richard Feynman called the “inconceivable nature of nature” and the best way I can illustrate it to you is by letting him tell it himself:
In the above video (which is well worth 5 3/4 minutes of your life) imagine that, instead of talking about electromagnetic waves, he’s talking about genetic code. That ought to give a fairly reasonable approximation for the stupendous audacity of the act of going about figuring out the lineage of all human kind.
So there’s room for more than one theory, here. On the other side of the Out of Africa explanation is multiregionalism. Multiregionalism states, in short, that the important event of human ancestry wasn’t the migrations from Africa, but what happened with the interactions between distinct populations (and yes, even species) of early humans once they settled down throughout Eurasia. Certainly this recent study seems to offer evidence in that direction. But I think the best approach is a sort of a compromise, what’s been called the “out of Africa again and again” hypothesis. In a nutshell, it states that yes, these three migrations were very important to the history of early humans, but there was also genetic cross-talk to varying degree between otherwise-isolated populations at that time. Furthermore, the third and final human migration (ie, ours) wasn’t a singular, Biblical exodus but probably happened over many thousands of years, further suggesting there was a slow exchange of genes going on. This seems most reasonable to me, and, given the apparent complexity of human lineage, leaves enough room for expansion when we come upon new information.
Of course, as long as there are different ways to go about interpreting data of such a complex nature, there’ll always be multiple theories and controversy surrounding those theories. And, really, that’s okay. “How did we get here?” is one of the most important questions humans can ask, and we shouldn’t hesitate to get our hands dirty – both figuratively and literally – and search for more clues. We’ve got plenty of genetic information now: about 7 billion subjects from which to choose. The trouble, I think, is a lack of a solid number of genetic samples from different times and places. That’s where the “literally” end of things comes up; the answers we’re looking for to the question of human ancestry are probably long-buried in the ground. We just gotta dig ‘em up, and, who knows, maybe in a couple of decades we’ll have figured it all out. I can’t wait to see what we find.
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