Stevens, Nettie Maria (1861-1912), an American biologist , is known for identifying the role of chromosomes in determining sex. In humans and other living things, chromosomes are the carriers ofinheritance—that is, the physical or behavioral characteristics passed from parents to their offspring.
Stevens was born July 7, 1861, in Cavendish, Vermont. At the time, educational opportunities for women were limited. Her family could afford to send her to a private school that was open to men and women. She graduated in 1880 and earned a teaching certificate in 1893. She went on to work as a teacher for many years. Following an interest in science, Stevens enrolled at Stanford University in California, where she earned a bachelor’s degree in physiology in 1899, and a master’s degree in 1900. She received her Ph.D. degree in 1903 at Bryn Mawr College in Pennsylvania.
Stevens’ most famous research involved chromosomes and how they determine sex in animals. Studying beetles , she found that the males made reproductive cells that had either one X-shaped chromosome or a smaller chromosome, now called the Y chromosome. Female beetles only produced reproductive cells with an X-shaped chromosome. Beetles that inherited one X chromosome from each parent developed into females. Beetles that inherited one X and one small chromosome developed into males.
Stevens published her discoveries in 1905. At the time, most scientists did not think chromosomes had any influence on sex determination. Most believed sex was somehow determined by environmental factors. Many scientists did not immediately accept that her discovery was correct. Stevens remained at Bryn Mawr for the rest of her career. She died on May 4, 1912.
