Human eggs are attracted to some sperm more than others

In a recent study from Stockholm University, experts have found that human eggs show preferential treatment when it comes to male sperm. While it is known that human eggs release chemicals to attract sperm, the research suggests that not just any sperm is chosen.

People invest a lot of time and energy in finding a suitable partner, but the mate selection process may not be entirely under our control. The new study has revealed that different eggs attract different types of sperm – that do not necessarily belong to chosen mates.

“Human eggs release chemicals called chemoattractants that attract sperm to unfertilized eggs. We wanted to know if eggs use these chemical signals to pick which sperm they attract,” said Professor John Fitzpatrick.

The research was focused on the interactions between sperm and the follicular fluids that surround the egg and contain sperm chemoattractants. The team set out to investigate whether substances in follicular fluids promote fertilization by specific sperm more than others.

“Follicular fluid from one female was better at attracting sperm from one male, while follicular fluid from another female was better at attracting sperm from a different male,” said Professor Fitzpatrick.

“This shows that interactions between human eggs and sperm depend on the specific identity of the women and men involved.”

The study revealed that eggs did not always attract more sperm from their partner compared to sperm from another male.

Professor Fitzpatrick explained that sperm have only one job, which is to fertilize eggs, so it does not make sense for them to be picky. On the other hand, eggs stand to benefit from selecting high quality or genetically compatible sperm.

“The idea that eggs are choosing sperm is really novel in human fertility,” said study senior author Professor Daniel Brison, the scientific director of the Department of Reproductive Medicine at Saint Mary’s Hospital.

“Research on the way eggs and sperm interact will advance fertility treatments and may eventually help us understand some of the currently ‘unexplained’ causes of infertility in couples.”

“I’d like to thank every person who took part in this study and contributed to these findings, which may benefit couples struggling with infertility in future.”

The study is published in the Proceedings of the Royal Society B.

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By Chrissy Sexton, Earth.com Staff Writer