Researchers found men of higher intelligence have better quality sperm
They can often be overlooked in favour of their handsome counterparts.
But brainboxes should stop despairing because research shows they are more virile than other men.
Scientists have shown that bright men have better sperm.
They produce more of it and it is of higher quality, suggesting they are better-equipped to start a family than their intellectually inferior friends and colleagues.
Researchers from the Institute of Psychiatry at King's College London made the link after comparing archived data on 425 Vietnam War veterans.
This dated back to 1985, when the men had given sperm samples as part of an extensive medical and undergone intelligence testing.
Comparing the two clearly showed that the brainiest men had the best quality sperm.
Total sperm count was higher, as well as sperm concentration and ability to swim, the journal Intelligence reports.
What is more, the finding could not be explained by factors known to affect health such as smoking, drinking and obesity, said researcher Rosalind Arden.
She said: 'We took two characteristics that seemed, on the surface, unlikely to be associated with each other - intelligence and sperm quality - and tested whether there was a statistical relationship between them.
'We found a small positive relationship: brighter men had better sperm.
'This association wasn't caused by habits like avoiding smoking or drinking - the big hitters of health.'
The finding feeds into recent research showing intelligence is linked to many aspects of health, including lifespan.
While it could be argued that brainy folks lead healthier lives, Miss Arden believes IQ is an outward sign of good genes.
If the genes involved in intelligence also have many other functions in the body, brainy people could expect to be fitter and more fertile.
Similarly, flaws that impair intelligence could harm health and the ability to become a parent.
Miss Arden said: 'We were interested in testing the idea that if most of our genes act on many characteristics (not one gene, one trait), there might be a weak but discoverable relationship right across all of our characteristics - from nose to toes.
'This set of weak relationships would give rise to a "fitness factor" in evolutionary terms.
'This does not mean that men who prefer Play-Doh to Plato always have poor sperm: the relationship we found was marginal.
'But our results do support the theoretically important "fitness factor" idea.'
Fertility experts, however, said that straining to complete crossword puzzles and other brain-sharpening games was likely to do little to improve a man's chances of fatherhood.
Dr Allan Pacey, a male fertility expert from Sheffield University, 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' womb, and therefore how well they both function in adult life, rather than suggesting that playing Sudoku can somehow stimulate more sperm to be produced.