New research shows that men with a lot of brothers are more likely to have a lot of children themselves, as they are likely to be more fertile.

The findings were published in the Asian Journal of Andrology, and the research also support the theory that parents with genes for good male fertility are more likely to have boys.

Experts from the University of Sheffield compared the traveling speed of the sperm of 500 men with their family make-up.

“We found the greater number of brothers rather than sisters a man has, the faster his sperm is, increasing the likelihood of fertility,” said Dr. Allan Pacey. “Lots of brothers is also an indication that the man’s parents have strong male fertility genes, and they would then be passed on  to the son. 

“The results are very surprising and could provide genetic insights into why some men are more fertile than others.

“It does, however, give food for thought about the importance of genetics for sperm motility and may open the way to more studies in this area,” he added.

Sperm activity, or “motility,” is known to be a major factor influencing male fertility.  

“We are very intrigued by this finding and hope other researchers examine their data sets in a similar fashion,” said Jon Slate, professor of evolutionary genetics at the University of Sheffield.

“If our results can be replicated we think it provides some evidence that humans have experienced what evolutionary biologists like to call ‘sexual conflict.’ The idea behind this is that genes that make males reproductively successful make females reproductively unsuccessful, and vice versa.”

The researchers said it did not mean men with a large number of sisters should worry, and they did not look at whether women with lots of sisters are likely to be more fertile, as it is much more difficult to measure.

It does, however, make sense that a man with many brothers would be more fertile, as his father clearly proved to be.

James Gilbert | Elite.