The female reproductive tract is cleverly shaped to weed out weak sperm.
That’s the claim made by scientists at New York’s Cornell University, who say a series of ‘pinch points’ – such as a narrowing between the uterus and fallopian tubes – is the biological equivalent of an assault course.
As a result, only the strongest sperm cells can push their way through the bottleneck to reach the egg, creating a quality control process for fertilisation.
The finding could help improve fertility screenings and improve a couple’s chances of conceiving.
‘If you look at the anatomy of the reproductive system in mammals, you can see that the dimensions of the canal that leads to the egg is not constant,’ said Dr Alireza Abbaspourrad, a chemist and lead author on the study.
‘The overall effect of these strictures is to prevent slow sperm from making it through and to select for sperm with highest motility.
‘At some points it is extremely narrow so that only a few sperm can pass while others fail.’