Women’s bodies can weed out ‘unwanted’ sperm, study finds

Men can get rejected even after sealing the deal.

Contrary to popular belief, the fastest sperm don’t always finish first. Various chemicals in the female reproductive system can also determine which sperm are successful, according to a new study published Wednesday in the journal Proceedings of the Royal Society B.

“The whole reproductive tract of the female seems to have evolved to filter out ‘unwanted’ spermatozoa,” Jukka Kekäläinen, a biology professor at the University of Eastern Finland who co-authored the study, told CNN.

Specifically, the cervix acts as a reproductive bouncer of sorts — both rejecting “abnormal” sperm, while aiding swimmers that give the woman’s offspring the best chance of survival, per the research. A prior study by the same team found that a woman’s follicular fluid serves the same purpose, CNN reports.

To test the organ’s selective function, the team combined all possible variations of cervical fluid of nine women with the sperm of eight men, and then compared swimmers’ finishing rate to the genotype of each participant.

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