Not so random after all: Human egg cells choose which sperm is the lucky winner

[H]ormones present at ovulation can drive a woman to choose a cocky, confident man with a slight stubble and more masculine features. Men can sniff out an ovulating woman just by smelling her T-shirt, while women appear to prefer the smell of a man with dissimilar genes, which could give her offspring a boost up the evolutionary ladder.

A fascinating new study finds those chemical-based preferences continue even after sex. Human eggs appear to “choose” which sperm will become the lucky winner in conceiving a baby.

“Human eggs release chemicals called chemoattractants, which leave a sort of chemical breadcrumb trail that sperm use to find unfertilized eggs,” said study author John Fitzpatrick, an assistant professor in the department of zoology at Stockholm University in Sweden.

“What we didn’t know until this study is those chemical breadcrumbs act differently on sperm from different males, in effect choosing which sperm is successful,” Fitzpatrick added.

And here’s the extraordinary finding: A woman’s egg doesn’t always agree with her choice of partner.

“We expected to see some sort of partner effect, but in half of the cases the eggs were attracting more sperm from a random male,” Fitzpatrick said. “The most likely explanation for this is that these chemical signals allow females to choose males who are more genetically compatible.”

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