Posted by:
SL Cabbie
(
)
Date: March 09, 2011 06:07PM
That means I have to negotiate this frickin' dark and treacherous highway myself... Well, here goes, and any other serious anthros or geneticist-types who want to chime in, please do...
First thing, to "saviorself" (I love that one!): I would get a copy of Jared Diamond's "Guns, Germs, and Steel" about human migration patterns and history. It's not the last word on the subject--there never is such a thing--but it's damn good...
JMHO, but Jim's post needs to define "Genetic Drift" in order to clarify matters. And really, the issue is "genetic variability" and just how diverse certain populations are in terms of the number of "original founding DNA contributions" that are present in a given population.
We know Africa was the original homeland of all of our ancestors because the quantities of identifiable and measureable DNA differences (mitochondrial, from the mother, Y-Chromosome from the father, and "autosomal" within the cell nucleus, the most complex of all) on that continent are demonstrably more numerous and variable than anywhere else.
Mitochondrial DNA (mtDNA) which is passed on from mother-to-child with the father making no contribution (there may be rare exceptions, but this is pretty universal) was the first type of DNA evaluated in this manner. It's relatively short ("only" 16,569 "letters") but long enough to yield statistical precision to help pinpoint when changes in those "letters" occurred via a mutation.
See if you can decipher some of what this Wiki article is saying, and you'll be on your way...
http://en.wikipedia.org/wiki/Human_mitochondrial_geneticsSo if we find a sequence such as AACCTTGTC (it would be much longer, of course) among a population of Africans, and we find similar sequences across the Indian Subcontinent (one known migration route), we can infer what happened. Similarly, if we suddenly see a "AACCTTATC" emerge in populations in India that isn't found in Africa, we can then reasonably infer the mutation arose in that neighborhood (or has to be accounted for by another explanation), and then if we find the new sequence both north (say China) and south (Borneo), we have deduced a probable "route on the map" that early human migration patterns followed.
Okay? BTW, "Genetic Drift" can be understood in part as something as simple as the "number of blond-haired children in Utah." The original "founding population" here was small, but there were large numbers of Scandavians (and blonds from Britain, often with Viking ancestry). Hence, since they've definitely "multiplied and replenished Zion" (displacing the native Shoshones, Utes, Paiutes, and Goshutes), there are larger numbers of blond-haired individuals here than elsewhere.
Such factors require reasonable explanations within the hypotheses being evaluated to account for their presence...
And now to the article at hand, which makes me really nervous because USA Today is strictly a "popular journal," and science reporters are often notorious for misinterpreting material published in peer-reviewed science journals (which, again, are not the last word, but are generally credible).
We know that in the "Out of Africa" migration, people crossed from Africa to Asia. Determining exactly where is problematic, but that is the shortest distance with Yemen probably the most likely candidate.
So that involves East Africa. The study cited offers a claim with supporting evidence that humans arose in South Africa rather than East Africa... So it essentially becomes an anthropological "Where was the Garden of Eden" question...
>Modern humans may have evolved in southern Africa, not eastern Africa as previous research had indicated. A study of genetic markers from six hunter-gatherer groups there found that they have the highest levels of genetic diversity in the world.
>It is currently believed by many in the scientific community that modern humans originated in eastern Africa. That's where the earliest anatomically modern skulls have been found. Also, populations from outside of Africa are made up of subsets of the genetic diversity found there.
Cue up the music for the drama about to appear on the stage... Diamond has some excellent insights on the subtle "politics of scientific consensus," BTW...
I will criticize the author of this piece for not clarifying whether this was a study involving mitochondrial or autosomal DNA (it looks autosomal to me), and that definition of "SNP's" was particularly obtuse ("the researchers looked at 580,000 SNPs, or 'snips among human populations, especially hunter-gatherer peoples in Africa.' These are single-nucleotide polymorphisms, DNA sequence variations that are different between members of the same species. They're often called 'genetic fingerprints,' because each individual has a distinct set of snips."). That looks like a bit of buzzword jockeying rather than a genuine grasp of what was being said.
Edited 1 time(s). Last edit at 03/09/2011 06:17PM by SL Cabbie.