Today, thanks to S., I read an absolutely fascinating post on linguistic diversity in pre-historic Europe that I’m sure will be worth reading to some of you. To get you excited about it, here is just one idea I learned from it that I had never realised before: when the last proto-Indo-Europeans lived can be determined from what inventions the Indo-European languages have words in common for (wool? yoke? wheel?). The other thing of interest I read today was a comment on the Milford Wolpoff post, dealing with gene flow.
While the “linguistic” and “genetic” flows are both really fun to think about and share some similarity, both in broad pattern, and simply because they are related to one another, one of them is actually a lot easier to grasp intuitively for me.
The timescale of “language flow” is probably unsurprising. But it’s the timescale of gene flow that is incredibly counterintuitive. And not just now, when people routinely migrate across the entire world, but for thousands of years before that. For instance, when do you think the last common ancestor for all humans on earth right now lived? Try to guess, unless you happen to know. Was it 1,000 years ago? 10,000? 100,000? 1,000,000? Or was there even such a person?
Well, did you guess 4,000 years ago? Unless you knew the answer or are a Biblical literalist, you probably didn’t. But, as far as we know, that’s right. About 4,000 years ago, after the great pyramids were already built and writing was long invented, there probably lived a person whom all of us, from me to the Dalai Lama to James Altucher to someone checking in on the blog from the Amazon jungle, are descendants of. To me this is the most counterintuitive thing I have ever learned in genetics, or, possibly, at all.
Dad points out that in his opinion, there is nothing at all groundbreaking in the post on European linguistic diversity. Some of the things said there were new to me, but that does not make them new per se. He also adds that not only is the when of PIE determined from the invention of technologies with cognate names in IE languages, the where is also partially determined from looking at what animals and plants have cognate names – and then mapping where such an ecosystem would have occurred.
Furthermore, let me caution that the MRCA claim for human population is not without controversy. This is reasonable, since the claim is incredibly tendentious, as I mentioned. It is based, as it necessarily has to be, on mathematical modelling, which involves a myriad assumptions. However, most of those assumptions seem to me to be suitably conservative. For instance, a migration rate of 1 person per 10 generations over the Bering Straight, given archaeologically documented continued contact, does not to me seem outlandish. If you are interested, you should check out the Nature paper by Rohde, Olson and Chang (pdf link). Having read it, I am somewhat less cavalier about claiming 4,000 as a good guess for the number. Still, the upshot, is not in the number 4,000 but in the realization that, given gene flow, the MRCA lived much, much more recently than the “Great Human Diaspora” occurred.