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hpisbi t1_jdqk78v wrote

Reply to comment by artaig in TIL that the ratio of male births to female births is 51/49%, and it's thought the ratio of X and Y chromosomes in the man's sperm is most likely the cause. by iKickdaBass

there are some other theories, including that Y chromosome sperm swim slightly faster than X chromosome sperm or that female embryos have a slightly higher chance of miscarrying. so they’re saying that the current view is that the ratio of X and Y sperm produced is what makes the difference, not the other theories.

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