Great Women In History: Nettie Maria Stevens

Nettie Maria Stevens, a scientist and biologist, accomplished more in her short life than most of us will – given many more years on this earth. The men around her, doing similar research, felt that women were capable of doing experiments, but not as competent to fully understand the results. Nettie Stevens’ focus of research was in cytology, and in particular, working with the chromosomal theory of inheritance, particularly in reference to sex determination. T.H.Morgan, head of the Biology Department at Bryn Mawr, wrote an obituary of Nellie Stevens, belittling her importance in the lab and basically said she was just a glorified lab technician. Earlier, however, BEFORE she passed away, he described her as the most successful and capable graduate student he had ever had. Nettie was obviously competent enough to get a Ph.D as well as a professorship and is known for the fabulous results that the men around her had never been able to achieve.

Born in 1861 in Vermont, Nettie went to a small college and was at first a teacher and librarian. Soon, she decided to return to her studies and received her B.A. from Stanford in 1899, and her M.A. In 1900. Then on to Bryn Mawr College, receiving her Ph.D in 1903. Although a relatively obscure research biologist, in 1905, she wrote a paper with the long-winded title, “Studies in Spermatogenesis with Especial Reference to the “Accessory Chromosome.” It became one of the 20th century’s major scientific breakthroughs, showing that the chromosomes known as “X” and “Y” were responsible for determining the sex of individuals. This ended the long-standing scientific debate as to whether sex was determined by heredity or other factors.

Her work on sex determination was published as a Carnegie Institute Report. In this study she looked at sex determination in the common mealworm. Investigating mealworms, she found female cells contained 20 chromosomes, but male cells contained 19 large chromosomes and one very small one. She showed that the X body was paired with a 20th, a much smaller, chromosome in meiosis. She proposed that these two chromosomes be called X and Y, and explained that females contained two X chromosomes.

Although Nettie had collaborated with Thomas Hunt Morgan, one of her professors at Bryn Mawr, most of her work was carried out as an independent investigator. Her work in the field of genetics has largely been ignored because the credit for the discovery of X and Y chromosomes and their role in determining gender was instead given to Edmund B. Wilson, one of Nettie’s instructors at Bryn Mawr. Wilson had read Steven’s manuscript on chromosomal patterns before publishing his “own theory.” Along with another Bryn Mawr professor, T.H.Morgan, they shared the Nobel Prize for the “supposed” discovery. Our hats are off to Nettie and her perseverance.