On this day in 1861 was the birth of Nettie Stevens, an early American geneticist who was one of two researchers to discover and describe sex differences in chromosomes. She was born in Vermont and later moved with her family to Massachusetts, where she graduated Westford Academy in 1880. After teaching for a few terms she went on to Westfield Normal School (now known as Westfield State University) where she was the top of her class and finished the four-year program in only two years. She then went on to Stanford University to earn her B.A. and her M.A., and complete another year of graduate work.
Her studies were eventually continued at Bryn Mawr, where she eventually earned her Ph.D., after receiving a graduate scholarshop in biology and being named a President’s European Fellow, allowing her to study for some time in Germany. After earning her PHD, she went on to continue her studies, including work on germ cells in aphids, and a study on “spermatogenesis”, as well as regeneration, single-cell organsms, sperm and egg development, and more.
In her research done at Bryn Mawr College, she was one of the first American women ever recognized for their contributions to science. It was in her work in experimental morphology that she determined the sex differences in chromosomes during a study of insects. It was her discovery that was the first time anyone observed differences in chromosomes and linked it to physical differences, i.e., physical sex. She began this research when she was in her 30s, in 1905, performing a number of experiments on a range of insects and figuring out that physical sex depended on the absence or presence of the Y chromosome. It was Stevens who discovered the Y chromosome (though they weren’t named until later) by studying mealworms.
Despite her discoveries, which included 38 publications, she never managed to attain a full position at her university. In addition, the discovery of sex chromosomes is largely attributed not to Stevens, but to her colleague and mentor, E. B. Wilson (a man). Wilson published his work around the same time, but he believed in environmental factors and didn’t come to the same conclusion about sex determination in chromosomes until after he read Nettie’s work. His paper was later republished, with “thanks” to Nettie, and in time he got most of the credit and was known largely as the originator of the discovery.
Nettie died of breast cancer in 1912, just after she was offered a research professorship at Bryn Mawr. She was only 52 years old and had only earned her Ph.D. nine years prior.