It is common knowledge that we generally determine the sex of someone as female (XX) and male (XY) by their chromosomes. While most people would credit this discovery to Thomas Morgan, the honor actually belongs to Nettie Stevens. Nettie’s discovery became the first of its kind to link chromosomes to physical characteristics [1]. Nettie was born in 1861 in Cavendish, VA to Ephraim Stevens, a carpenter, and Julia Adams. After her mother died and father remarried, the family moved to Westford, MA in 1865, where Nettie was enrolled in private school along with her sister Emma. They both proved to be highly exceptional students and once they graduated both went into teaching. Having enjoyed teaching, Nettie enrolled at a teachers college in Westford and completed their four-year program in two years, once again proving her high intellect.

She continued teaching for many years after that until 1896 when, at 35 years of age, she enrolled at Stanford University in their physiology bachelor’s program. After graduating in 1899, she remained in California to study organisms and cells at Stanford’s Hopkins Seaside Laboratory [1]. She returned to Stanford to complete her master’s degree in cell biology and organisms in 1900. In 1901, Nettie started going to Bryn Mawr College, near Philadelphia, to work on her Ph.D. in cytology (cells). It was during her time at Bryn Mawr College that she met Thomas Hunt Morgan, one of her professors, who was the head of the biology department [1]. Owing to her excellent work and talent, Nettie was offered the opportunity to study abroad from 1901 to 1902 at the Naples Zoological Station in Italy and the University of Würzburg in Germany. She studied under Theodor Boveri in Germany and was conducting research into chromosomal inheritance, which she would follow up on in her postdoctoral work [1]. In 1903, she graduated with her Ph.D. and continued to teach as well as research in order to keep her funding.

Nettie began conducting experiments on chromosomal heredity for her postdoctoral research and, in 1905, she published her work in the Carnegie Institute Report that showcased sex determination in mealworms [2]. She showed that sex was determined by the X and Y chromosomes. Her results were considered controversial because of her gender as well as the fact that the idea that chromosomes were used for sex determination went against the current thought at the time [3]. Edmund Wilson, at Columbia University, also discovered the link between chromosomes and sex determination at the same time as Nettie, furthering support for this new idea.

Before she could continue her research, Nettie died of breast cancer in 1912. Despite her late entry into science and short time as a researcher, Nettie managed to accomplish quite a lot. Unfortunately, Thomas Morgan took most of the credit for her work and relegated her to a simple technician that helped him [4]. Thomas Morgan won the Nobel Prize in Physiology or Medicine in 1933 for his (and Nettie’s) research on the role that chromosomes played in sex determination [5]. Fortunately, researchers looked into Morgan’s work and found that he supported other, incorrect, views of sex determination that did not align with the work that he presented as his own. This gave credence to the fact that Nettie was the real person who deserved to be awarded. Now at least, we know how amazing Nettie was and can appreciate her work. She lived in a time when women were not expected or encouraged to seek out education, especially not a Ph.D. level of education. Nevertheless, she was encouraged by her family, friends, and own self-determination to persist towards these goals.

Photo of Nettie Stevens. Acquired from Wikipedia Commons