Science, Now + Beyond

A woman discovered the Y chromosome

Happy birthday, Nettie Stevens!

If you took basic high school biology, you learned that each human cell nucleus contains 23 pairs of chromosomes – 22 pairs of “autosomes”, which look identical in males and females, and 1 pair of “allosomes”, or what we know as sex chromosomes. Call me a nerd, but I think it is wildly fascinating how something as simple as a single chromosome can influence countless traits to determine whether an individual is male or a female. We all know about this, but who actually discovered it? You can thank badass Nettie Stevens for that, and while you’re at it, wish her a happy birthday too!

Who was Nettie Stevens?

Nettie Maria Stevens was born on July 7, 1861 (HAPPY BIRTHDAY NETTIE!) in Vermont. After graduating from Westford Academy, she taught a number of courses at a high school including physiology, zoology, and math. She moved on from three years of teaching to continue her education at Westfield Normal School where she graduated at the top of her class.

She followed that by attending Stanford University where she received her B.A. degree in 1888 and her M.A. in physiology and cytology. Stevens continued her studies in cytology at the women’s college, Bryn Mawr, just outside of Philadelphia, where she got her Ph.D. She received many scholarships and accolades for her work –something that was very impressive for that time as a woman.

Nettie Stevens

What did she contribute to science?

Nettie Stevens was one of the first American women to have her work recognized as a solid contribution to science. In 1905, using insects, she discovered that chromosomes are different among the sexes. Stevens identified the Y chromosome, the chromosome that attributes to male characteristics, in a mealworm Tenebrio. Unfortunately though, as badass and accomplished as she was, Nettie Stevens was never granted a full regular university teaching position. She passed away on May 4, 1912 of breast cancer. Her Ph.D advisor, Thomas Hunt Morgan, included a piece of a recommendation letter he wrote on her behalf in his obituary for Stevens in the journal Science. He wrote, “Of the graduate students that I have had during the last twelve years I have had no one that was as capable and independent in research as Miss Stevens.”

Though her lifespan was short, Nettie Stevens was so incredibly accomplished—publishing nearly 40 papers among numerous other achievements. She truly changed the field of science and genetics with her discovery. It’s crazy that we don’t even learn about her in school, while her discoveries laid the groundwork for what we know about sex determination. I know that I have and will continue to be inspired by her work as a scientist, a researcher, and an all around badass woman!