Originally Posted by bombusben
The genetic uniqueness that is used to categorize populations is from non-coding, hypervariable segments of mtDNA. These segments have no phenotypic expression, are not subjected to selection or meiotic recombination, and have vastly different mutation rates from nuclear DNA. They are genetic fossils.
Thanks bombusben for your insightful comments. You're on the ball!!
Mitochondrial DNA was chosen for two reasons ... first, as you mention, the rate of mutation is much higher than in nuclear DNA and second because of the predictable mode of inheritance. The initial focus of organizations such as The Human Genome Diversity Project were to answer basic questions about our genetic origins. Their questions could be satisfied by simply tracing lineage through mtDNA. This is not to say that the same could not be accomplished through the use of somatic sequence, it's just that mtDNA is easier.
Originally Posted by bombusben
I agree with you that to some unknown extent there is very complicated correlation between variation in the nuclear genome and physical capability. However there is nothing to suggest that hypervariable mtDNA segment mutation is consistent with the nuclear loci responsible for an individual's phenotypic expression of athletic ability. Therefore assuming that these traits follow a geographical distribution or evolutionary history is a complete shot in the dark.
I would agree with this 100%. Specifically, I would bet that there's zero correlation between inheritance patterns of mtDNA and that of genomic DNA. Were it not for parallel studies of Y chromosome migration patterns within populations, I would say that you're right. But if Y (also with a simple mode of inheritance relative to somatic DNA) can be traced and demonstrated to contain common segments among a population, then the same will almost certainly hold true for somatic DNA.
Originally Posted by bombusben
Take for instance the sickle cell allele. The fact that it is present in various ethnically distinct lineages “blacks, South Americans, Southern Europeans and Middle Easterners” suggests that nuclear DNA traits don’t always correlate well with the evolutionary history suggested by mtDNA analysis.
While I haven't seen the data, what makes you think that those populations aren't connected gentically? Specifically, might they share alleles in other loci independent of those that determine skin color, height, etc.
Originally Posted by bombusben
On top of that, I'm not sure what sort of inferences a reasonable person can be made about a population's "abilities and/or limitations" based upon the frequency of a single loci mutation like sickle cell or super hemoglobin (if it is also a single loci mutation). If the hemoglobin mutation is heritable, it is likely to spread to numerous populations much the same way sickle cell has. Will the Ethiopians be good at XC skiing too?
Again, I agree. What we're grasping for is some tractable means of tracing populations. Population geneticts have logically focused upon regions of the genome that are pehaps under less selective pressure than others ... highly conserved gene sequences and non-coding DNA. Sickle cell is a great example of a heritable trait that one would hope will be selected against a thousand years from now (although given that sickle cell anemia sometimes doesn't manifest until after child bearing age, this may never happen). Mutations that create competitive athletic advantages will likely never come under the same type of pressue and may be tracable in the future. As for Ethiopians being good at XC, I suspect that they could be under the right environmental conditions ... i.e. snow 8 out of 12 months of the year. Elite Ethiopian athletes certainly have the aerobic capacity.
You're keeping me on my toes ...
-mark