Bio #4: Nettie Stevens Mystery Cache

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Nettie Stevens was the person who first discovered that sex is determined by x and y chromosomes. She was born on July 7, 1861 in Cavendish, Vermont. From 1881 to 1883, Nettie attended the State Normal School in Westfield, Massachusetts. She did extremely well in school and in 1896, started attending the prestigious Stanford University. She earned a B.A. there in 1899 and received her masters in 1900. She moved across the country to Pennsylvania, where in 1903, Stevens obtained a PhD from Bryn Mawr College. In 1904, she wrote a breakthrough paper on cytology (the study of cells as fundamental elements of living things) with Thomas Hunt Morgan, after studying that topic for several years. Dr. Morgan was famous in his own right, establishing the “Fly Room,” a genetic laboratory at Columbia that produced a series of nobel prize winners. 

Stevens failed to obtain a full university position, however, she achieved a research career She recorded 38 publications, including several contributions which confirmed ideas of chromosomal heredity. As a result of her research, Stevens provided critical evidence for Mendelian and chromosomal theories of inheritance.

Nettie Stevens made her largest contribution to science in 1905 when she published her work on mealworm/beetle genetics. This discovery, that the sex of an organism was determined by what x and y chromosomes. She observed that the chromosomes of male and female beetles were different, specifically for one of their chromosomes. A similar discovery  was also made by another scientist, Edmund Beecher Wilson, in the same year. Wilson received more credit for the discovery, but Stevens’ model was more accurate.

Before her discovery, people had been arguing over whether an individual’s sex was inherited or impacted by things in the environment such as nutrition, temperature, or weather. For instance, many reptiles determine the sex of their offspring from the temperature of the eggs. Like nearly all breakthrough discoveries, scientists did not embrace the new discovery at first, and kept on insisting that it might be the environment that was responsible for an individual’s sex.

After making her discovery, Nettie Stevens kept on researching the chromosomes in insects. From 1905 until she passed away in 1912, she was an associate in experimental morphology (the study of the structure of plants) at Bryn Mawr College. According to Vox, the New York Times’ obituary for her said this: “She was one of the very few women really eminent in science, and took a foremost rank among the biologists of the day.”