A team from the UK Institute of Psychiatry analysed data from former USA Vietnam soldiers. They found that those who performed better on intelligence tests tended to have more - and more mobile - sperm.
The study, which appears in the journal Intelligence, appears to support the idea that genes underlying intelligence may have other biological effects too. For example, if tiny mutations impair intelligence, they might also harm other characteristics, such as sperm quality.
It was previously believed that the better health characteristics found in more intelligent people were lifestyle related, for example people of high intelligence are more likely not to smoke and to take exercise.
The latest study tested the gene theory by taking two characteristics that seemed unlikely to be associated with each other - intelligence and sperm quality.
They found a small, but statistically significant link, and were able to show that this could not be explained by unhealthy habits, such as smoking or drinking alcohol.
The study was based on 425 men who undertook several intelligence tests and provided semen samples.
The researchers found that independently of age and lifestyle, intelligence was correlated with all three measures of sperm quality - numbers, concentration, and ability to move.
