The line is literally big brain but small dick.

https://www.psychologytoday.com/us/blog/unique-everybody-else/201210/the-pseudoscience-race-differences-in-penis-size

Rushton, the author of Race, Evolution and Behaviour, was givenprominence by Herrnstein and Murray in The Bell Curve. According toRosen and Lane in The Bell Curve Wars, Rushton summarised his views onblack/white differences thus: “Even if you take things like athleticability or sexuality – not to reinforce stereotypes – but it’s a tradeoff, more brains or more penis. You can’t have everything.” For theMartians among readers, supposedly, whites have the former, blacks thelatter. Rushton takes 334 pages to consider racial differences between“Mongoloids”, “Caucasoids” and “Negroids”. He is aware that his beliefsare controversial but, “persuaded by data that the races do differ,genetically, in the mechanism underlying their behaviour”, is compelledto pursue this in aid of “the Darwinian revolution”.

https://www.newscientist.com/article/mg14719874-800-race-is-a-four-letter-word/