Natural selection favors the intelligent. The evidence is right here in our civilization. We are smarter than our distant ancestors, Australopithecus, Homo erectus, Cro-Magnon — that is a given. The question is, did intelligence evolve because the smarter members of the population could avoid getting killed off? In prehistoric times, this would involve finding the best foods and avoiding enemies; in modern times this means staying in shape, not smoking, and avoiding violent lifestyles. Or were intelligent people more likely to reproduce because they attracted mates? We all know intelligence is sexy, but has it always been so? Or are intelligence, health, and reproductive ability linked genetically, even before the connection to behavior?

As reported in The Economist, a study led by Rosalind Arden of King’s College in London might bring us a tad closer to the answer. Her team analyzed data taken in 1985 from 435 Vietnam veterans that included intelligence scores based on Spearman’s g AND sperm samples that were tested at the time for sperm count, concentration, and motility.

Ms Arden found 425 cases where samples had been collected and analysed from unvasectomised men who had managed to avoid spilling their seed during the collection process and had answered all the necessary questions for her to test her hypothesis, namely that their g values would correlate with all three measures of their sperm quality. They did. Moreover, neither age nor any obvious confounding variable that might have been a consequence of intelligent decisions about health (obesity, smoking, drinking and drug use) had any effect on the result. Brainy men, it seems, do have better sperm.

This doesn’t tell us what caused the correlation. Vietnam veterans are, intelligent or not, the product of millions of years of natural selection. There may be something deep in our limbic systems that causes us to seek out intelligent mates when we can get them, at least someone more intelligent than our prehistoric ancestors, for childbearing purposes. Or the traits may have been linked genetically many generations ago, and continue no matter who mates with who, because people of below average intelligence are still reproducing (which explains why you often feel surrounded by idiots). The Economist article posits the possibility that intelligence is just another manifestation of general healthiness, as is sperm count and attractiveness as a mate. Better specimens are just plain better specimens all over.

Still, it’s nice to know that brainy men have better sperm. Should you ever be in a position to use that as a pickup line, it’s available with citable research.