Nettie Maria Stevens was born in Cavendish, Vermont, to a middle-class family. At the age of three, after her mother’s death, her father remarried, and they moved to Westford, Massachusetts. Her father, who was a carpenter, insisted that his daughters will receive a good education, and he saved money that enabled him to send Stevens and her sister Emma to Westford Academy, where they were among the only three women to graduate between 1872-1883. At 19, she moved to Lebanon, New Hampshire, and for a year, she taught at the local high school, saving money to continue her education. In 1881 she enrolled in the State Normal School, completing four years degree in only two years, scoring the highest in her class. At the age of 35, she entered Stanford University, and after receiving her B.A. in Biology, she continued to study for an M.A. At 39, Stevens began her doctoral studies at Bryn Mawr College, focusing mainly on the regeneration of multicellular organisms and the development of sperm and eggs. After receiving her Ph.D., she was appointed to a Research Fellow position, then to a Reader in Experimental Morphology, and afterward to an Associate in Experimental Morphology, where she stayed until she died. Her Ph.D. research on regeneration led her to explore the process of sex determination. She was interested to know if sex passed through genetic inheritance. She observed mealworm beetle and discovered that the males’ reproductive cells have two chromosomes – a small one and a large one (today known as Y and X chromosomes), while females have only one (the X chromosome). Stevens concluded that the chromosome carried by the male is what determines the sex of the embryo – paring with the small chromosome becomes a male (XY), and pairing with the large chromosome becomes a female (XX). When she worked on her research, another researcher, named Edmund Wilson, made a similar observation, and at the beginning, he was the only one to receive credit for the findings. Over the next 11 years, Stevens continued her research and teachings at Bryn Mawr College as well as publishing more than 30 papers, continuing to contribute to the field of genetic sciences until her last days. She passed away at the age of 50 from breast cancer. Read more...