Intelligence

And of course, the eugenicists also like to make claims that various groups have more or less innate intelligence. And of course it is always the groups that they don't like which turn out to have lower innate intelligence: how convenient for them.

And, of course, when you actually look, you find that measured intelligence in given groups has changed enormously over periods of less than a century. Which is far, far too short a time for any genetically-driven change to happen.

Because, of course, the measures of intelligence are junk.

Again: the only safe thing to say about eugenics is that people who believe in it are not very smart. And they're usually racists.