Well, that contradicts what you said above: "Looking at genotype printouts, one often couldn't determine which race a person belongs to."
So what? That doesn't suggest that the 4 (or 3 or 5) races are the best (or even an adequate) way of describing human genetic diversity.
You keep missing the point: racial classifications were never intended
to be "descriptions of genetic diversity," and did not have that communicative purpose. They refer only to a complex of physiological characteristics, most of them empirically evident, associated with particular geographic regions of the planet. Claims such as, "There are no such things as race," or, "Races don't exist," or, "Race is just a social construct," etc., are fatuous, post-modernist nonsense. Those differences do have a genetic basis, just as does the concept of sex, which PM-ers are also (ridiculously) trying to dismiss as a "social construct."
Among the salient DNA findings: there is more gentic diversity in Africa than in the rest of the world put together. This being the case, why would any geneticist find "Negroid" to be one race, but Caucasoid, Mangoloid, Aborigine (etc) to be separate races? That makes no sense.
Same answer --- because the extent of genetic diversity is not the criterion for descriptive racial classifications. A person is Negroid if he has most of the defining, empirical characteristics of that race, regardless of the diversity in other genes members of that group may have.
You seem not have read your own links. From the NYT piece:
"In this way, a consensus was established that among human populations there are no differences large enough to support the concept of 'biological race.' Instead, it was argued, race is a 'social construct,' a way of categorizing people that changes over time and across countries.
"It is true that race is a social construct.[*] It is also true, as Dr. Lewontin wrote, that human populations 'are remarkably similar to each other' from a genetic point of view.
"But over the years this consensus has morphed, seemingly without questioning, into an orthodoxy. The orthodoxy maintains that the average genetic differences among people grouped according to today’s racial terms are so trivial when it comes to any meaningful biological traits that those differences can be ignored.
"The orthodoxy goes further, holding that we should be anxious about any research into genetic differences among populations. The concern is that such research, no matter how well-intentioned, is located on a slippery slope that leads to the kinds of pseudoscientific arguments about biological difference that were used in the past to try to justify the slave trade, the eugenics movement and the Nazis’ murder of six million Jews.
"I have deep sympathy for the concern that genetic discoveries could be misused to justify racism. But as a geneticist I also know that it is simply no longer possible to ignore average genetic differences among 'races.'
"Groundbreaking advances in DNA sequencing technology have been made over the last two decades. These advances enable us to measure with exquisite accuracy what fraction of an individual’s genetic ancestry traces back to, say, West Africa 500 years ago — before the mixing in the Americas of the West African and European gene pools that were almost completely isolated for the last 70,000 years. With the help of these tools, we are learning that while race may be a social construct, differences in genetic ancestry that happen to correlate to many of today’s racial constructs are real.
"Recent genetic studies have demonstrated differences across populations not just in the genetic determinants of simple traits such as skin color, but also in more complex traits like bodily dimensions and susceptibility to diseases. For example, we now know that genetic factors help explain why northern Europeans are taller on average than southern Europeans, why multiple sclerosis is more common in European-Americans than in African-Americans, and why the reverse is true for end-stage kidney disease.
"I am worried that well-meaning people who deny the possibility of substantial biological differences among human populations are digging themselves into an indefensible position, one that will not survive the onslaught of science."
* In the trivial sense that all concepts expressible in language are "social constructs."