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During the change associated with 20th century, biologist Nettie Stevens had been driven to fix a systematic secret which had perplexed mankind for millennia. The secret had been therefore simple but daunting: Why do men be girls and boys become girls? Inside her pioneering just work at Bryn Mawr College, Stevens — whoever birthday celebration is today, July 2 — found the intercourse chromosomes that produce the huge difference.
Before Stevens, we had been utterly clueless regarding how embryos become men or girls
Because of Stevens’s work — and also the work that built upon it — we now understand that sex is hereditary, and that dads’ sperm in particular determine the intercourse of offspring.
However for nearly all of history, this concern ended up being a mystery that is absolute plus it yielded some interesting theories.
Aristotle believed a sex that is child’s decided by the human body heat for the dad while having sex. “Aristotle counseled men that are elderly conceive within the summer time should they wanted to have male heirs, ” the textbook Developmental Biology describes. Continue reading Nettie Stevens discovered XY intercourse chromosomes. She did not get credit because she had two X’s.