Kenan Malik in his blog Pandemonium wrote possibly the best article on human race and the current controversy between "race realists" and biologists and geneticists who say that race is not a biological reality. The controversy flared up a bit recently due to a review, written Jan Sapp (a biologist) of two books that insist that race has no biological validity. Sapp agrees, and states that race as "type" or as "genetic population" is a misconception, and that human races are sociocultural constructs. According to Sapp, most biologists would agree on this. I think that Sapp is correct in stating that most biologists agree with this. But Jerry Coyne disagreed with Sapp and wrote that "human races exist in the sense that biologists apply the term to animals". Jonathan Marks (a biological anthropologist) got really aggravated because he says that Coyne is ignoring all that anthropology has to say about the subject. Marks writes: "Of course the discovery that people in different places are different is a trivial one. At issue is the pattern of those differences and its relation to the classification of the human species. To equate the existence of between-group variation to the existence of human races is to miss the point of race entirely. Race is not difference; race is meaningful difference". Malik's position is that both sides of the debate are wrong. And both are right. His article is long, but worth every word. He explains why most biologists or geneticists refuse to think of human races as being biologically valid, emphasizing that the more we know about human genomics and genetics, the fuzzier the picture becomes. His conclusion is that race is a social category but one which can have biological consequences. I'm in agreement with this. Read the entire article, you will not get bored or regret it.
Knowing something about a person's ancestry can be medically relevant because certain diseases or disease alleles are exclusive to certain ancestry groups (like Tay-Sachs in Ashkenazi Jews, for example), BUT read this paragraph to understand why even that statement, that race is biologically relevant because it's medically relevant is not that clear cut, either. The two paragraphs below were among my favorite in Malik's article.
Yet race is not necessarily a good guide to disease. We all know, for instance, that sickle cell anaemia is a black disease. Except that it isn’t. In the USA, the presence of the sickle cell trait can help distinguish between those with, and without, African ancestry. But not in South Africa. In South Africa, neither blacks nor whites are likely to possess the trait. Sickle cell is not a black disease, but a disease of populations originating in areas with high incidence of malaria. Some of these populations are black, some are not. There are four distinct sickle cell haplotypes (a haplotype is a set of linked genes) two of which are found in equatorial Africa, one in parts of southern Europe, southern Turkey, and the Middle East, and one in central India. The majority of people in Africa, including those in southern Africa, do not suffer from sickle cell disease.
Most people know, however, that African Americas suffer disproportionately from the trait. And, given popular ideas about race, most people automatically assume that what applies to black Americans applies to all blacks and only to blacks. It is the social imagination, not the biological reality, of race that turns sickle cell into a black disease.
The only one thing I'm 100% sure about after reading this article is... I want this puzzlegirl's phone number.
I also loved this passage for its clarity, and because I really admire the 90-year old geneticist Luca Cavalli-Sforza.
1. ‘A race is a geographically and genetically distinct population’
The first claim defines a race as a ‘geographically and genetically distinct population’. It is a concept derived from Ernst Mayr’s ‘population’ definition of race. A race, the biologist Alice Brues writes, is ‘a division of a species which differs from other divisions by the frequency with which certain hereditary traits appear among its members’. Races are distinguished from each other, not because they possess unique, fixed genetic features, but because one differs from another statistically in the frequencies of particular alleles. It does not matter what genes differ, or how many, or to what degree, just that some do to some extent.
The trouble with this definition, though, is that if we were to test for enough genes, we could find a statistical difference between virtually any two populations. As Cavalli-Sforza explains,
Our experiments have shown that even neighbouring populations (villages or towns) can often be quite different from each other… The maximum number of testable genes is so high that we could in principle detect, and prove to be statistically significant, a difference between any two populations however close geographically or genetically. If we look at enough genes, the genetic distance between Ithaca and Albany in New York or Pisa and Florence in Italy is most likely to be significant, and therefore scientifically proven.
Cavalli-Sforza adds that while ‘the inhabitants of Ithaca and Albany might be disappointed to discover that they belong to separate races’, the ‘people in Pisa and Florence might be pleased that science had validated their ancient mutual distrust by demonstrating their genetic differences.’
If any population in the world can be defined as a ‘race’, then the concept becomes meaningless. As Cavalli-Sfroza puts it in his understated way, ‘classifying the world’s population into several hundreds of thousands or a million different races’, is ‘impractical’. The anthropologist Vincent Sarichresponds that ‘it is for Nature to tell us’ what is a ‘reasonable’ number of races. But if the people of Ithaca and Albany are to be treated as distinct races, then Nature is probably telling us to trash this particular definition of race.
Also, here is a great free article on human genome diversity, and FAQs. Very, very good. Published 2 years ago in Trends in Genetics (Cell Press).
From that article, I want to highlight this paragraph about skin color because very often people think races should be classified just on the basis of skin color.
What about skin color?
Wouldn’t it be better to simply classify people according to skin color? As a matter of fact, no. With an estimated 70 loci affecting pigmentation, and different metabolic pathways leading to the production of the two main pigments, eumelanin and pheomelanin, skin phenotypes present the challenges of all complex traits . The basic color depends on the proportion of the two main pigments, the size of
melanosomes, and their location in the epidermis. Variation has been related to mechanisms of sexual  or natural  selection, but a general preference for lightskinned partners, predicted by models of sexual selection, is not supported by data . The strong correlation between melanin levels and average UV radiation (UVR) intensity is probably due to geographically variable selection, because melanin protects against excess UVR, but hinders vitamin D synthesis when UVR is low . People
living at the same latitude and subjected to similar selective regimes (e.g. Europeans and East Asians) have similar skin color, but that color is the product of convergent evolution in which different mutations determine similar phenotypes . Therefore, clusters of people with similar skin colors would include individuals with very different origins and genotypes
Rosenberg and his colleagues studied 377 DNA sequences from 1056 individuals spread across 52 populations worldwide using a computer programme calledstructure. Structure takes any set of data, and attempts to find a rational way of dividing it into as many groups as it is asked to. In this study, structure was asked to divide up the populations of the world (represented by the 52 DNA samples) into two, three, four and five groups according to how similar or dissimilar were their DNA sequences. When the scientists asked the computer to divide the population of the world into two groups, one group comprised of DNA samples from Africa, Europe and western Asia and the second group of samples from eastern Asia, Australia and the Americas. When the DNA data was divided into three groups, the group consisting of populations from Eastern Asia and the Americas remained unchanged. But the populations of sub-Saharan Africa were separated from those of Europe and Western Asia. In other words, the three groups were the populations of sub-Saharan Africa, those of Europe and Western Asia, and those of Eastern Asia, Australia and the Americas. When asked to create four groups, structure created a new group by separating the populations of eastern Asia and the Americas. And when asked to break the data into five groups, structure kept all the other groups as they were but separated off the populations of Australasia from the rest of Asia.
And now there are even newer measurements, with more human genomes, meaning much more than 377 DNA sequences!