More brothers could mean faster sperm and better fertility

Men with more brothers than sisters may have faster swimming sperm and are more likely to have increased fertility according to new research carried out by experts from the University of Sheffield.

Scientists from the University of Sheffield in collaboration with researchers at Brown University in America found a correlation between the swimming speed of a man’s sperm and the number of brothers he has.

The findings, reported online in the Asian Journal of Andrology, support previous theory that parents with genes for good male fertility are more likely to have boys.

mediumDr Allan Pacey, Senior Lecturer in Andrology at the University of Sheffield, said: “The results are very surprising and could provide genetic insights into why some men are more fertile than others but at the moment have no clinical relevance to how we might manage and treat male infertility. 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.”

In a study of 500 men attending semen analysis as part of infertility investigations, the team used sophisticated computer technology to accurately measure how fast the men’s sperm swam and then correlated this information with how many brothers or sisters each had in his family.

When the data were analysed, the researchers were surprised to find that men with mostly brothers had faster sperm than men with mostly sisters. Although this does not mean that siblings directly influence sperm, there is a correlation which could offer an insight into how different sperm speeds in men have evolved.

Dr Jim Mossman, Postdoctoral Researcher at Brown University, who collected the data during his PhD studies in Sheffield and who led the research said: “This is certainly not a smoking gun as a reason for infertility in men. However, it would be interesting to test whether the same relationships are observed in other human populations as well as in other species. Likewise, would we observe similar associations when looking at female fertility? If the relationship between sex-bias in the number of children and fertility is a more universal phenomenon, then we may expect female fertility to follow a similar pattern, albeit in the opposite direction.”

Jon Slate, Professor of Evolutionary Genetics at the University of Sheffield added: “We are very intrigued by this finding and hope other researchers examine their datasets in a similar fashion. 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.”

Additional information

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The University of Sheffield

With nearly 25,000 students from 125 countries, the University of Sheffield is one of the UK’s leading and largest universities. A member of the Russell Group, it has a reputation for world-class teaching and research excellence across a wide range of disciplines. The University of Sheffield was named University of the Year in the Times Higher Education Awards 2011 for its exceptional performance in research, teaching, access and business performance. In addition, the University has won four Queen’s Anniversary Prizes (1998, 2000, 2002, and 2007).

These prestigious awards recognise outstanding contributions by universities and colleges to the United Kingdom’s intellectual, economic, cultural and social life. Sheffield also boasts five Nobel Prize winners among former staff and students and many of its alumni have gone on to hold positions of great responsibility and influence around the world. The University’s research partners and clients include Boeing, Rolls-Royce, Unilever, Boots, AstraZeneca, GSK, ICI, Slazenger, and many more household names, as well as UK and overseas government agencies and charitable foundations.

The University has well-established partnerships with a number of universities and major corporations, both in the UK and abroad. Its partnership with Leeds and York Universities in the White Rose Consortium has a combined research power greater than that of either Oxford or Cambridge.


For further information please contact:

Paul Mannion
Media Relations Officer
The University of Sheffield
0114 222 9851