Three attacks on my book A Troublesome Inheritance have appeared on The Huffington Post's blog this month. For readers puzzled by the stridency and personal animus of these compositions, I'd like to explain what is going on.

The issue is how best to sustain the fight against racism in light of new information from the human genome that bears on race.

My belief is that opposition to racism should be based on principle, not on science. If I oppose racism and discrimination as a matter of principle, I don't care what the science may say because I'll never change my position. As it happens, however, the genome gives no support to racism, although it does clearly show that race has a biological basis, just as common sense might suggest.

Many social scientists, on the other hand, have long based their opposition to racism on the assertion that there is no biological basis to race. I doubt they personally believe this and suspect that they oppose racism on principle, just as I do. But they believe that other people, less enlightened and intelligent than they, will not abandon racism unless told that everyone is identical beneath the skin. So whenever someone points out that race is obviously biological, defenders of the social science position respond with attacks of whatever vehemence is necessary to get the inconvenient truth-teller to shut up.

For many years this tactic has been surprisingly effective. It takes only a few vigilantes to cow the whole campus. Academic researchers won't touch the subject of human race for fear that their careers will be ruined. Only the most courageous will publicly declare that race has a biological basis. I witnessed the effects of this intimidation during the 10 years I was writing about the human genome for The New York Times. The understanding of recent human evolution has been seriously impeded, in my view, because if you can't study the genetics of race (a subject of no special interest in itself), you cannot explore the independent evolutionary histories of Africans, East Asians and Europeans.

The attacks on my book come from authors who espouse the social science position that there is no biological basis to race. It is because they are defending an ideological position with a counterfactual scientific basis that their language is so excessive. If you don't have the facts, pound the table. My three Huffington Post critics -- Jennifer Raff, Agustín Fuentes and Jonathan Marks -- are heavy on unsupported condemnations of the book, and less generous with specific evidence.

Despite their confident assertions that I have misrepresented the science, which I've been writing about for years in a major newspaper, none of these authors has any standing in statistical genetics, the relevant discipline. Raff is a postdoctoral student in genetics and anthropology. Fuentes and Marks are both anthropologists who, to judge by their webpages, do little primary research. Most of their recent publications are reviews or essays, many of them about race. Their academic reputations, not exactly outsize to begin with, might shrink substantially if their view that race had no biological basis were to be widely repudiated. Both therefore have a strong personal interest (though neither thought it worth declaring to the reader) in attempting to trash my book.

It would try the reader's patience to offer a point-by-point rebuttal of the three reviews, so I will address just the principal arguments raised by each. Let's start with Raff, who asserts, "Wade claims that the latest genomic findings actually support dividing humans into discrete races." In fact, I say the exact opposite, that the races are not and cannot be discrete or they would be different species, but it's easier to attack an invented statement.

The human genome points to the overriding unity of humankind. Everyone has the same set of genes, so far as is known. Genes come in the alternative versions known as alleles, so one might expect next that races would be demarcated by alleles. But even this is not the case. In fact, the races are not demarcated at all. They differ only in relative allele frequency, meaning that a given allele may be more common in one race than in another. How that translates into the familiar differences in physical appearance between human races is a matter I explain in my book.

Because of these characteristic differences in allele frequency, geneticists can analyze the genome of someone of mixed race -- an African American, say -- and assign each segment to an African or European ancestor, an exercise that would be impossible if races did not exist. Also because of differences in allele frequency, researchers analyzing human genetics around the world have found in surveys dating back to 1994 that people cluster in groups that coincide with their continent of origin.

Raff and Marks take issue with one of these surveys, Rosenberg et al. 2002, which used a computer program to analyze the clusters of genetic variation. The program doesn't know how many clusters there should be; it just groups its data into whatever target number of clusters it is given. When the assigned number of clusters is either greater or less than five, the results made no genetic or geographical sense. But when asked for five clusters, the program showed that everyone was assigned to their continent of origin. Raff and Marks seem to think that the preference for this result was wholly arbitrary and that any other number of clusters could have been favored just as logically. But the grouping of human genetic variation into five continent-based clusters is the most reasonable and is consistent with previous findings. As the senior author told me at the time, the Rosenberg study essentially confirmed the popular notion of race.

The chief point extractable from Fuentes' review is that since I don't say exactly many races there are, races can't exist. This is a misunderstanding of the nature of continuous variation. People may disagree on the number of colors there are, but that doesn't mean colors don't exist. Humans cluster into five continental groups or races, and within each race there are further subclusters. So the number of human races depends on the number of clusters one wishes to recognize. Contrary to Fuentes' belief, this has no bearing on whether or not races exist.

The wider issue arising from these three reviews is that the social science position on race that they represent is obscurantist, counterfactual and outdated. As I show in my book, understanding the nature of human racial variation lends no support to racism. But such understanding is essential for the simple reason that there is not one story of recent human evolution but at least five different stories, given that the populations on each continent have evolved largely independently of one another since the dispersal from Africa some 50,000 years ago.

By denying the existence of race, social scientists are intimidating biologists from pursuing this path. This is particularly exasperating given the fallacious nature of the belief that race must be denied if racism is to be quelled. The geneticist Theodore Dobzhansky observed, "People need not be identical twins to be equal before God, before the law, and in their rights to equality of opportunity." Unlike identical twins, we are not all clones. We exist as different races by virtue of our evolutionary histories. The recovery of this history is a legitimate subject of scientific inquiry, and from this advance of knowledge unimagined benefits may accrue.