Different women’s eggs attract different men’s sperm

Choosing your partner continues even after sex – human eggs can “choose” sperm.

According to a new study published in the Proceedings of the Royal Society B, human eggs appear to “choose” which sperm will become the lucky winner in conceiving a baby.

The study conducted by the Stockholm University and Manchester University NHS Foundation Trust, suggests that human’s eggs use chemical signals to attract and choose sperm. It means women’s eggs prefer some men’s sperm over others.

John Fitzpatrick, an Associate Professor at Stockholm University, said, “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.”

Scientists studied the sperm response to follicular fluid, which surrounds eggs and contains sperm chemoattractants. They determine how those chemical breadcrumbs act differently on sperm from different males.

Professor Fitzpatrick said, “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.”

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

The study, in other words, suggests that women’s eggs do not always agree with the women’s choice of partner. Also, eggs did not always attract more sperm from their partner compared to sperm from another male.

Sperm’s job is to fertilize eggs. Thus, it doesn’t make sense for them to be choosy. Eggs, on the other hand, can benefit from picking high quality or genetically compatible sperm.

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

The University of Manchester Honorary Professor added: “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 the future.”

Journal Reference:
  1. Chemical signals from eggs facilitate cryptic female choice in humans. DOI: 10.1098/rspb.2020.0805

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