Today's Google doodle honours Nettie Stevens, pioneering geneticist who worked out that sex is determined by chromosomes

Today's Google doodle celebrates the 155th birthday of Nettie Stevens.

Today's Google doodle celebrates the 155th birthday of Nettie Stevens.

You've just got to love the history lessons we get to learn thanks to Google's wonderful daily doodles. Today, Google is celebrating the birthday of Nettie Maria Stevens, a pioneering geneticist who overcame the hurdles of being a 19th century woman in STEM to be one of the first female scientists recognised for her work. Her research into genetic sex determination fundamentally changed our understanding of what makes someone born with male or female biological markers. 

Before Stevens' important work, it was assumed the sex of babies was determined by the mother, which often led to women being blamed for failing to produce a boy. Remember the femicidal King of England, Henry XIII who killed two of his six wives and formed a whole new church because the existing Catholic one wouldn't let him divorce the others? It's understood his main reason for having Anne Boleyn executed was that she "failed to produce" him a male heir (depite having a son, who apparently didn't count because he was stillborn). A treacherous woman indeed.

Anyway, back to Stevens. Born in Vermont in 1861 to a middle class family, she had little opportunities open to her for education or professional work, but she was lucky enough to attend a good school and became utterly passionate about biology. She graduated and became a teacher at the age of 19, and spent the following decade and a half alternating work as a teacher and librarian with further study, eventually enrolling at Stanford University at 35.

Nettie Stevens

Nettie Stevens

At the ripe old age (for those days!) of 39, Stevens finally got her big break and began working as a research scientist, looking into the process of sex determination by studying mealworms, of all things. Around 1905, she worked out that females made reproductive cells only with X chromosomes, while males made both X and Y, and concluded that the sex is therefore determined by the male reproductive cells (the Y ones end up with male biology!) 

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And so our modern understanding of biological sex was born. 

Stevens, who would have been 155 years old today, had her life and blossoming career tragically cut short by breast cancer just as a research fellowship was about to be opened for her at Bryn Mawr College outside Philadelphia. 

In her obituary, a male colleague who had praised her while she was alive belittled her achievements by suggesting she was little more than a lab technician.

Here's hoping plenty of people have learnt the truth about her achievements after clicking on a little Google illustration today.