Cultural lag is the polite term for habits and hypotheses that never die.

From More Markers, More Differentiation, and People Know What Race They Are Anyway by James Thompson.  He is addressing a claim which has been around for years and has been wrong for that entire period.  

The claim is that race is a social construct because within group variation is greater than between group variation.  One of those claims which has just enough of a patina of complexity to appear plausible and yet which is not.

Cultural lag is the polite term for habits and hypotheses that never die. They become immune to refutation by virtue of constant repetition. One such meme, due to Lewontin (1972), asserts that there is more genetic variation within genetic groups than between them, and therefore that…… er, ….there is no difference between the groups/there is no genetic difference between genetic groups/any differences between groups cannot be due to genetic reasons/asserting that genetic group differences are discriminable by genetics would be arbitrary and wrong/genetic groups do not exist.

I had never been convinced by these arguments, on the simple basis that genetic groups are clearly visible, and sustain themselves by genetic means, and are usually halved by admixture. Also, it was only a vague thought, but it seemed to me that a test could still be significant with relatively small mean differences if the sample size was high enough. Probably not relevant in genetics, I mused.

In fact, the ease with which you can separate two genetic groups depends, like all discriminations and all clustering, on the number of markers available for the discrimination and clustering techniques being used. With only a few markers, discrimination is difficult, and error prone. As you increase the number, allocation to different groups becomes progressively easier.

So, to counter the endless echo of the original hypothesis, I am trying to put together a list of papers which explain and test the issue.

Tim Bates explains that Lewontin based his claims on blood type markers: about as advanced as it was possible to be in 1972, but hopeless to identify genetic clustering, therefore doomed to render a false negative. The 2005 paper by Neil Risch (now cited 400 times) shows how inadequate that procedure was by showing one can now predict race near perfectly with random sets of SNPs.

He then goes on to excerpt the key research in the cited paper which undermines the "race is a social construct" hypothesis.  The key evidence is:

We have analyzed genetic data for 326 microsatellite markers that were typed uniformly in a large multi-ethnic population-based sample of individuals as part of a study of the genetics of hypertension (Family Blood Pressure Program). Subjects identified themselves as belonging to one of four major racial/ethnic groups (white, African American, East Asian, and Hispanic) and were recruited from 15 different geographic locales within the United States and Taiwan. Genetic cluster analysis of the microsatellite markers produced four major clusters, which showed near-perfect correspondence with the four self-reported race/ethnicity categories. Of 3,636 subjects of varying race/ethnicity, only 5 (0.14%) showed genetic cluster membership different from their self-identified race/ethnicity. 

There is further discussion.  The final paragraph is a nice epitaph for the never-particularly-credible hypothesis.  

In sum, you get a near perfect correspondence between genetic measures and the common racial labels, with a misclassification rate of a mere 14 per 10,000. Some of this is due to the admixed “other” category, and perhaps some existential confusion in the others, but 9,986 in 10,000 subjects can master the art of looking in a mirror and noting which race they most resemble, a task beyond the wit of some academics.

Reminds me of George Orwell's comment in Notes on Nationalism.

One has to belong to the intelligentsia to believe things like that: no ordinary man could be such a fool.

Or Bertrand Russell's comment in My Philosophical Development.

This is one of those views which are so absurd that only very learned men could possibly adopt them.