Men with the highest IQ also have the healthiest sperm, according to an evolutionary psychologist, reports the Telegraph.

The qualities of being smart and funny may have evolved to become signals to women looking for a partner with healthy genes, the psychologist said.

The results come from a study of 400 Vietnam War veterans. The men underwent mental tests and provided sperm samples. Those who got high scores in the intelligence tests had high counts of healthy sperm. Those with lower intelligence test scores had fewer and less healthy sperm.

Sperm quality is directly related to brain quality, believes Professor Geoffrey Miller, from the University of New Mexico, who conducted the research.

Professor Geoffrey Miller thinks human traits like language, intelligence and humour evolved in both men and women because these qualities are attractive to the opposite sex.