Background

Stevens was born July 7, 1861, in Cavendish, Vermont, to a middle-class family that had lived in New England for five generations. Her father was Ephraim Stevens, a carpenter. Her mother was Julia Adams, who died when Nettie was just two years old.

In 1865 her father married Ellen Thompson. The Stevens family, consisting of father, step-mother, Nettie, and her younger sister Emma, then relocated to Westford, Massachusetts.

Education

At that time, education for women was not common, but Stevens was lucky enough to attend the Westford Academy in 1881-1883, which was open to men and women of all nationalities. When she graduated at age 19, she became a teacher even though she still longed to further her education. She taught for only three terms while saving her money to attend the Westfield Normal School, a teachers' college.

Stevens's pattern of working, saving, and returning to school would repeat itself after graduation from Westfield. In 1896 at age 35, she enrolled at Stanford University, earning a Bachelor of Arts in 1899 and a Master of Arts in 1900. She began graduate school at Bryn Mawr College, which included a year of study (1901-1902) at the Zoological Station in Naples, Italy, and at the Zoological Institute of the University of Würzburg, Germany. She received a Doctor of Philosophy degree from Bryn Mawr in 1903 and remained at the college as a research fellow in biology for a year, as a reader in experimental morphology for another year, and as an associate in experimental morphology from 1905 until her death.

Career

At age 39, Stevens began working as a research scientist, and the next 11 years would be the most productive of her life. Stevens was interested in the process of sex determination. While studying the mealworm, she found that the males made reproductive cells with both X and Y chromosomes whereas the females made only those with X. She concluded that sex is inherited as a chromosomal factor and that males determine the gender of the offspring.

At the time, the chromosomal theory of inheritance was not yet accepted, and it was commonly believed that gender was determined by the mother and/or environmental factors. Most scientists did not embrace Stevens's theory immediately. Another researcher, Edmund Wilson, made a similar discovery at about the same time, but Stevens is generally considered to have made the larger theoretical leap (one which was ultimately proven correct). She was often overshadowed by Edmund Wilson, another researcher who independently made a similar discovery. Wilson was often credited with the discovery because of his other contributions and higher reputation, but his conclusions were not as strong or accurate as Stevens’. Stevens’ time in the spotlight would not arrive until after her death when progress in science would be followed by progress in the way we recognize revolutionary women.

Stevens continued to do research and teach at Bryn Mawr and Cold Spring Harbor Laboratories for the rest of her life. Her scientific career started late and ended much too soon when she died of breast cancer on May 4, 1912. However, in the intervening decade prior to her death, she had managed to contribute more to her field than many scientists have with much longer careers.

Achievements

• Nettie Stevens was one of the first female scientists to make a name for herself in the biological sciences.
  
  Nettie Maria Stevens developed the idea of sex determination by chromosomes. Her work established the importance of chromosomes in heredity and helped Thomas Hunt Morgan interpret the early genetic results from Drosophila.
  
  Stevens was inducted into the National Women's Hall of Fame in 1994.

Works

More photos

• book

  • Further Studies on the Ciliate Infusoria, Licnophora and Boveria

    (This work has been selected by scholars as being cultural...)

  • Further Studies on the Ciliate Infusoria, Licnophora and Boveria

    (Nettie Stevens's work on the Ciliate Infusoria, Licnophor...)

  • Studies On The Germ Cell Of Aphids

    (Nettie Stevens's work on the germ cell of aphids.)

  • Studies in spermatogenesis 1905

Views

Stevens’s earliest field of research was the morphology and taxonomy of the ciliate protozoa; her first published paper, in 1901, had dealt with such a protozoan. She soon turned to cytology and the regenerative process. One of her major papers in that field was written in 1904 with zoologist and geneticist Thomas Hunt Morgan, who in 1933 would win the Nobel Prize for his work. Her investigations into regeneration led her to a study of differentiation in embryos and then to a study of chromosomes. In 1905, after experiments with the yellow mealworm (Tenebrio molitor), she published a paper in which she announced her finding that a particular combination of the chromosomes known as X and Y was responsible for the determination of the sex of an individual.

This discovery, also announced independently that year by Edmund Beecher Wilson of Columbia University, not only ended the long-standing debate over whether sex was a matter of heredity or embryonic environmental influence but also was the first firm link between a heritable characteristic and a particular chromosome. Stevens continued her research on the chromosome makeup of various insects, discovering supernumerary chromosomes in certain insects and the paired state of chromosomes in flies and mosquitoes.

Quotations: "How could you think your questions would bother me? They never will, so long as I keep my enthusiasm for biology; and that, I hope will be as long as I live."

Personality

Nettie Maria Stevens grew up in America just after the Civil War. Beyond teaching, nursing, or secretarial work, little opportunity was available to women looking for a profession; most simply hoped to marry well. Stevens, however, would not go that route. She was a teacher, but it was only a means to an end. Stevens wanted to be a scientist and worked her way through school, eventually reaching her goal and earning her place in the history of genetics.

Stevens was an exceptionally bright student, and, although teaching was not her first love, her enthusiasm for science made her a caring and dedicated teacher.

Quotes from others about the person

• "Her single-mindedness and devotion, combined with keen powers of observation; her thoughtfulness and patience, united to a well-balanced judgment, account, in part, for her remarkable accomplishment." - Thomas Hunt Morgan.
  
  "Modern cytological work involves an intricacy of detail, the significance of which can be appreciated by the specialist alone; but Miss Stevens had a share in the discovery of importance, and her work will be remembered for this when the minutiae of detailed investigations that she carried out have become incorporated in the general body of the subject." - Thomas Hunt Morgan.
  
  "Miss Stevens’s work is characterized by its precision, and by a caution that seldom ventures far from the immediate observation. Her contributions are models of brevity - brevity amounting at times almost to meagerness." - Thomas Hunt Morgan.

Connections

Nettie Stevens had never been married and had no children.

Father:

Ephraim Stevens

Mother:

Julia Adams

step-mother:

Ellen Thompson

Sister:

Emma Julia Stevens

teacher:

Oliver Peebles Jenkins

colleague:

Thomas Morgan

References

• Scientific revolutionaries of 1905: Einstein, Rutherford, Chamberlain, Wilson, Stevens, Binet, Freud
  1979
• Forgotten Women: The Scientists
  2018