Nettie Maria Stevens Biography (1861-1912)


Nettie Maria Stevens was born in Cavendish, Vermont, on July 7, 1861. She wasan outstanding student, who finished high school during a time when most women never even reached that educational level. Still, her career opportunitieswere limited. Stevens earned her living as a school teacher and librarian, as did most unmarried women in the late 1800s. But unwilling to spend her whole life teaching high school, she sought further education. Since most universities did not admit women, she enrolled in Westfield Normal School, a teacher's college. After earning her certificate, she spent the next thirteen yearsworking and saving in hopes of attending one of the country's few co-ed universities.

In 1896, she entered Stanford University in California, where Stevens received her master's degree in 1900. She was eventually attracted to Bryn Mawr College, where she conducted her postgraduate work under Thomas Hunt Morgan. (Another distinguished member of the faculty, Edmund Wilson, left the staff justbefore Stevens arrived.) Morgan, impressed with Stevens's brilliant work as afirst-year student, helped her get a fellowship to study abroad. Her work inGermany with Thomas Boveri on the role of chromosomes in heredity helped prepare the way for her later contributions to science.

Upon her return to the United States in 1904, Stevens won a grant from the Carnegie Institute that allowed her to do original research. At this time, despite all the chromosome observations, experiments, and theories, no one knew for certain how the sex of a baby was determined. Stevens decided to find out.In her studies with mealworms, she observed that there were distinct differences in the chromosomes of a male versus the chromosomes of a female. Upon further study, she found a perfect correlation between sex and chromosome type.The females always carried two X chromosomes, but males produced either a large X chromosome or small Y chromosome. If an egg were fertilized with spermcarrying the male's X chromosome, it would produce a female. If it were fertilized with the male's Y chromosome, it would produce a male. Stevens published her findings on May 23, 1905. However, Wilson knew of Steven's work and wassimultaneously conducting similar research. Wilson's paper, which essentially reached the same conclusions, was dated May 5, 1905, but was not publisheduntil August. Still, Wilson is usually given sole credit for the discovery, although he continued to acknowledge Stevens's work throughout his career.

Stevens remained at Bryn Mawr as a professor and researcher until her death of breast cancer. She died in Baltimore on May 4, 1912.

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