Nettie Stevens discovered XY sex chromosomes.
Nettie Stevens discovered XY sex chromosomes. She didn't get credit because she had two X’s. At the turn of the 20th century, biologist Nettie Stevens was driven to solve a scientific mystery that had perplexed humanity for millennia. The mystery was so simple but daunting: Why do boys become boys and girls become girls? In her pioneering work at Bryn Mawr College, Stevens discovered the sex chromosomes that make the difference. Today would be her 155th birthday. Google is celebrating her accomplishments today — she’s featured in the Google Doodle — and so should we. Before Stevens, we were utterly clueless about how embryos become boys or girls Thanks to Stevens’s work — and the work that built upon it — we now know that sex is hereditary, and that dads’ sperm in particular determine the sex of offspring. But for most of human history, this question was an absolute mystery — and it yielded some interesting theories. Aristotle believed a child’s sex ...