Tuesday, November 22, 2005

Man is more than one tree   posted by Razib @ 11/22/2005 09:21:00 PM

This is a short post which I will elaborate on later in a broader biological context, but Richard Sharpe's comment is something I want to respond to real quick: "If Greeks are Caucasian, then...Just how do you designate yourself...."

First, I'm not white, my ass is a rich brown, ergo, I'm not "Caucasian." The nerdy amongst us though might be familiar with the term "Caucasoid," which shares a relationship with Caucasian (there were very few non-white Caucasian/Caucasoids in the country when these terms became common). Well, operationally I don't think South Asians should really be considered Caucasoid (though Middle Easterners should, Middle Easterners-Europeans are a monophyletic clade in relation to Brownoids). On a phylogenetic tree, if I had to make one, I would make Caucasoids and Brownoids (my term) a monophyletic clade in relation to other races of man.

But there's a serious problem with this in my opinion. In The Real Eve Stephen Oppenheimer spun a grand genetic-historical narrative which culminated during the Last Glacial Maximum, about 30,000 years ago. It is from this point that Oppenheimer traces the origins of modern races. He states flat out that admixture has been minimal. Perhaps. Perhaps not. The problem with Oppenheimer's story is that it is rooted in mtDNA, which is passed only through the female line. This is neat, because it eliminates recombination between lineages, so you get a clean cladistic tree all the way back to a common ancestor with all the putative ancestral character states. But the vast majority of our DNA is recombinant, and not passed uniparentally. You look at many Latin Americans, and the mtDNA will tell you they are cousins to East Asians, while the NRY (passed through fathers) will tell you they are Iberians. This is the most extreme case, but I doubt it is the only one.

So back to Richard's question. The problem I have with answering stuff like this is that I'm a melange, as all people are. I can say that I suspect it is likely that vast majority of my ancestry can probably be traced to the South Asian subcontinent around 10,000 years ago, but my NRY and mtDNA might say something different. Our full ancestral complement does not decompose itself into a bushy cladistic tree, it a reticulated mish-mash, like a ball of spaghetti. I mean, we're not asexual, right? We're one species across which genes can flow in a sweeps. Well, tell that to the authors that are making tidy advances based on books that pedal neutral lineage markers as the family-tree writ large. Genealogy is big bucks, even in quasi-scientific garb.

And who forgot selection? (Natural and social)

P.S. I have to say, about 2/3 of my scientific posts probably are derived from a question from the comment boards. A lot of the time it is even a 2nd or 3rd order idea, not a direct response. So thanks.