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Nettie Stevens discovered XY intercourse chromosomes. She did not get credit because she had two X’s.

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During the change associated with century that is 20th biologist Nettie Stevens had been driven to fix a systematic secret which had perplexed mankind for millennia. The mystery ended up being therefore easy but daunting: Why do males be girls and boys become girls? Inside her pioneering just work at Bryn Mawr university, Stevens — whose birthday celebration is today, July 2 — found the intercourse chromosomes that produce the real difference.

Before Stevens, we were utterly clueless exactly how embryos become guys or girls

Because of Stevens’s work — additionally the work that built upon it — we currently realize that sex is hereditary, and that dads’ sperm in particular determine the sex of offspring.

However for nearly all of history, this concern had been a complete secret — also it yielded some interesting theories.

Aristotle believed a child’s sex ended up being decided by your body heat regarding the dad during intercourse. “Aristotle counseled senior males to conceive during summer when they wanted to have male heirs, ” the textbook Developmental Biology describes.

In 19th-century Europe, it absolutely was commonly thought that nourishment had been the answer to intercourse determinant. Bad nutrition resulted in males, good nourishment to females. Continue reading