It's from the book, "before the dawn," by nick wade. I'll gladly loan you my electronic copy of the book if you send me an email:
bpesta22@cs.com.
Selective citation from Wade’s book in my post here, so I hope there is some continuity when reading this. I also submit this is fair use, as I cite it for educational purposes, and the book is 322 pages long…
“…people of different races may hold in their genetics essential clues to human history since the fragmentation of the ancestral human population 50,000 years ago. Races presumably developed in part in response to the pressures experienced by each population, and the genetic changes involved in race may allow those pressures to be identified. …
…the starting point for the emergence of human races would have been the dispersal, within Africa, from the ancestral homeland some 50,000 years ago. Before people left for the world beyond, the human population in Africa had apparently fragmented, doubtless by geographical distance, into several different populations. As already noted, those who left Africa belonged to just one of these populations, those descended from the L3 branch of the mitochondrial DNA tree. They carried away in their genes only a subset of the African genetic diversity, meaning only some of the alleles of each gene. That fact alone set them on a potentially different evolutionary path…
…the emigrants eventually spread out over the rest of the globe and themselves fragmented into many even smaller populations. The smaller a population, the greater is the force of genetic drift, which reduces the num-ber of available alleles. Without interbreeding to keep the human gene pool mixed, the populations of each continent or region would over time have be¬come more distinct and less like the others….
…besides drift, another differentiating force on the world’s separate hu¬man populations would have been natural selection. Selection may have pressed particularly hard on the people who left the African homeland, since they would have had to adapt to radically new diet, terrain and climates. A particularly striking example of selection is a recently discovered gene vari¬ant that causes pale skin in Caucasians. Almost all African and Asians have the same, ancient form of the gene, which is known at present as SLC24A5. Some 99% or more of Europeans have a new version, which must have arisen after Caucasians and East Asians had become separate populations. The new version presumably became almost universal among Caucasians be¬cause the pale skin it conferred was of overwhelming advantage, whether for reasons of health or sexual attractiveness or both. A different gene, yet to be discovered, must give East Asians their pale skin…
…Marcus Feldman of Stanford University reached a very similar conclu¬sion. Instead of examining just a few markers, or sites on the DNA, as many previous studies had done, Feldman and his colleagues looked at 377 sites throughout the genome, a larger and more representative sample. This was done for each of 1,000 people from 52 populations around the world. A com¬puter was then instructed to group the individuals, based on their DNA dif¬ferences at the 377 sites, into clusters. They fell naturally into 5 clusters, corresponding to their five continents of origin—Africa, western Eurasia (Europe, the Middle East, and the Indian subcontinent), East Asia, Oceania and the Americas…
…Feldman’s method gives a glimpse of how deeply genetic markers may be able to reach into population history. The computer program used to sort the genome samples into continental clusters could also split an individual’s genome into different parts if the person was of mixed ancestry. People from the Hazara and Uighur of Central Asia, long a crossroads between east and west, emerged with genomes roughly half Caucasian and half East Asian in origin. The Surui, a fairly isolated people of Brazil, have genomes that are entirely American (in terms of the computer program’s 5 racial clusters…
…but people can now be objectively assigned to their continent of origin, in other words to their race, by genetic markers such as those used by Feldman. And Lewontin’s characterization of the differences he had found as trivial was as much a political as a scientific opinion. The degree of differentiation he had measured in the human population was similar to other estimates that put the value of global FST as between 10 and 15%. Sewall Wright, one of the three founders of population genetics and the inventor of the FST measure, com-mented that “if racial differences this large were seen in another species, they would be called subspecies."
