Do we are already selected?
Researchers from Stockholm University and Manchester University found, by testing the reactions of sperm to the follicular fluid that surrounds human eggs that Human eggs release compounds called chemoattractants which chemically communicates with sperm. The researchers exposed sperm to follicular fluid from two females (a partner and a non-partner) and observed where the sperm accumulated. Because sperm can’t be exposed to follicular fluid from two different people at once in natural circumstances (because that isn’t logically possible anyways), the team also tested sperm with two follicular fluids consecutively. All up, the researchers tested sperm and follicular fluid from 60 couples undergoing reproductive treatments.
“Follicular fluid from different females consistently and differentially attracts sperm from specific males,” the team wrote in their paper, finding that eggs attracted between 18 to 40 percent more sperm from their preferred males. But how do we know it’s not the sperm doing the choosing? One of the researchers, zoologist John Fitzpatrick from Stockholm University, explains that it doesn’t make sense for sperm to be the picky one, as sacrificing the swimmers doesn’t cost males much. “But for eggs, and women, there are a lot of extra costs that come after fertilisation such as the costs of pregnancy. Hence, because of these costs, eggs should be choosy about which sperm fertilise them.”