BJ&TheBear:

In walks the science:

In one of the most extensive of these studies to date, considering 1,056 individuals from 52 human populations, with each individual genotyped for 377 autosomal microsatellite markers, we found that individuals could be partitioned into six main genetic clusters, five of which corresponded to Africa, Europe and the part of Asia south and west of the Himalayas, East Asia, Oceania, and the Americas

<link>

And, having walked in, the science boldly announces an r-squared of.... 0.2.

As the synopsis says:

"They then show that allele frequency differences generally increase gradually with geographic distance. However, small discontinuities occur as geographic barriers are crossed, allowing clusters to be produced."

I.e., although there is wide variation among each geographic "race" there are "small discontinuities" from one to the next, which clustering software can detect.

From their prior publication, which they reference: "Within-population differences among individuals account for 93 to 95% of genetic variation; differences among major groups constitute only 3 to 5%." <link> (That's actual physical differences between all physical genes, total, including the obvious pigmentation, not differences in IQ) My editorial comment: Reminds me of those ads that try to sell you things that increase your gas mileage; it's always "up to 5%", i.e., big enough to be interesting, but too small to reliably detect without a scientific study like this.

(From fig. 6, summing up their best analysis; there's a linear relationship between genetic distance and geographical distance, so that every 5,000 miles adds about .01 to the genetic distance, no matter what the population (although some of the spreads are ten times that). No surprise. in addition to that, there's a jump of about .02 between Eurasia and East Asia, about .02 between Eurasia and Africa, and about .05 between East Asia and America (i.e. Native American) or Oceania. ) Again, what this boils down to: "Within-population differences among individuals account for 93 to 95% of genetic variation; differences among major groups constitute only 3 to 5%."