Hidden Histories: Nettie Stevens

Art by Malia Kuo.

Nettie Maria Stevens was born on July 7, 1861, in Cavendish, Vermont, where her family had lived for several generations. Still feeling the aftereffects of the Civil War, women in the US generally had few educational and professional opportunities. However, in part because of her father’s accumulated wealth, Stevens attended public schools, eventually graduating from Westford Academy at the age of nineteen. Stevens was a dedicated student, earning praise from teachers and peers alike. 

After graduation, Stevens became a high school teacher to save money to continue her education. Later, she attended Bryn Mawr College and pursued a graduate scholarship in biology. After just six months at Bryn Mawr, Stevens performed such brilliant work that she was awarded a fellowship to conduct research abroad. She studied at the Zoological Station in Naples, Italy and the Zoological Institute of the University of Würzburg in Germany. After earning her doctorate at Bryn Mawr, she continued to teach and research at the college until her death due to breast cancer in 1912.

Stevens studied morphology, the study of the forms of living organisms, and cytology, the study of the structure and function of plant and animal cells. Her research focused on sex determination, how biological sex and sex characteristics are determined in organisms. At the time of Stevens’ research, there were two major schools of thought on sex determination. Some believed sex was determined by external factors and others believed that sex was determined at the point of fertilization, not by the surrounding environment. Over the course of her research, Stevens noticed that male mealworms produced sperm with either a large chromosome (now known as the X chromosome) and sperm with a small chromosome (now known as the Y chromosome), but female mealworms only produced eggs with large chromosomes. She concluded that chromosomes, specifically on the paternal side, are responsible for sex determination. 

Despite Stevens publishing her groundbreaking discoveries, many credit Edmund Wilson, a geneticist who worked in the same fields as Stevens, for the finding. While Stevens and Wilson worked on chromosomal sex determination simultaneously, they arrived at the conclusion independently. In fact, Thomas Hunt Morgan, a mentor to Stevens who did not accept the theory of chromosomal inheritance at the time, is often credited with discovering the genetic basis for sex discrimination. Morgan even went on to win a Nobel Prize in 1933 “for his discoveries concerning the role played by the chromosome in heredity.”

Stevens is not the only female scientist whose contributions to science were not recognized as her own until long after her death. Others include Rosalind Franklin, who co-discovered the helical structure of DNA, and Esther Lederberg, who discovered a virus that infects E. coli bacteria, a widely used tool in the current study of genetics. This pattern indicates the Matilda effect: the repeated dismissal of scientific discoveries made by women in science. Stevens’ discoveries about sex determination are the basis for many advancements in research on Turner syndrome and Down syndrome, as well as developments in the chromosomal basis of heredity. Although Stevens dedicated much of her life to her education and research, making crucial contributions to the field of genetics, the highest position she ever reached was as an associate in experimental morphology at Bryn Mawr College. Thomas Hunt Morgan described her as more of a lab technician than a true scientist. Reporters at the time stressed Wilson’s discovery over Stevens’, even though Stevens stated her conclusions more explicitly. 

Without Stevens’ discoveries, it is impossible to know where the field of genetics would be today. Yet, like many other female researchers, her work has been consistently undervalued. There is limited research available on how to diminish gender bias in scientific fields. However, by continuing to acknowledge the contributions of female scientists, we can work to create a world where the Matilda effect does not exist—a world in which we celebrate Nettie Maria Stevens for her achievements.