Data from U.S. veterans suggests that smarter men produce more, and more agile, sperm.
According to the BBC, researchers at the Institute of Medicine examined sperm samples from 425 Vietnam War-era U.S. veterans, collected in 1985 by the U.S. Centers for Disease Control and Prevention. The scientists looked at the volume and mobility of sperm, as well as scores from a variety of intelligence tests taken by the veterans.
The team found that, after ruling out factors such as age and lifestyle, higher intelligence was correlated with all three measures of sperm health -- numbers, density, and mobility.
The relationship was not strong, lead researcher Dr. Rosalind Arden told the BBC, "but our results do support the theoretically important 'fitness factor' idea." That theory suggests that certain genes work together to make certain individuals fitter, healthier and smarter.
This connection probably starts in the womb, one expert said.
"The fact that it's possible to detect a statistical relationship between intelligence and semen quality in adult men probably says more about the co-development of brain and testicles when the man was in his mother's womb, and therefore how well they function in adult life, rather than suggesting that playing Sudoku can somehow stimulate more sperm to be produced," Dr. Allan Pacey, a fertility expert at the University of Sheffield, U.K., told the BBC.
The findings were published in the journal Intelligence.