Brainy men really are the sexiest, claim scientists who have discovered a link between intelligence and virility.
The findings could explain why some of the world's most intelligent men have so many female admirers no matter their physical attractiveness.
They also suggest that being smart and funny might have developed as a signal to women looking for a mate with healthy genes.
The research, by the evolutionary psychologist Professor Geoffrey Miller of the University of New Mexico, centred around a study of 400 Vietnam War veterans who were put through extensive mental tests and were also asked to provide sperm samples.
According to the test results, it was found that men who scored high on a battery of intelligence tests boasted high counts of healthy sperm.
Whereas, low scorers tended to have fewer and more sickly sperm.
Professor Miller, who is speaking at a conference of the Association for the Study of Animal Behaviour at Oxford University, believes that sperm quality was directly related to brain quality.
The two traits could have evolved together as a way to advertise good genes, he said.
He believes a number of human traits including language, intelligence, humour and selflessness may have evolved because they are attractive to the opposite sex.