Nettie Stevens

Nettie Maria Stevens was born on July 7, 1861, in Cavendish, Vermont, and died on May 4, 1912. She was an American biologist who was one of the first scientists to discover the chromosomes relating to the determination of sex in humans. Stevens first attended the State Normal School in 1881-1883. In 1896, she decided to move on to study at Stanford University, where she earned a Bachelor's degree in 1899 and a Master's degree in 1900. Stevens started doctoral studies in biology at Bryn Mawr College and a year of study at the Zoological Station in Naples, Italy, and at the Zoological Institute of the University of Wurzburg, Germany, where she received a Ph.D. Nettie Stevens was then given an assistantship by the Carnegie Institute. Her starting field of research was experimental morphology and taxonomy. She soon changed course and began focusing on cytology and the regenerative process of cells. One of her most significant papers was written with zoologist and geneticist Thomas Hunt Morgan, which won a Nobel Prize.

Stevens began investigating regeneration and the differentiation of embryos, which led to her study of chromosomes in different insect biologies and thus the discovery of X and Y chromosomes determining the sex of a fetus. She discovered this while studying mealworms, which showed that males had reproductive cells with both X and Y chromosomes, while females only had the X chromosome. This helped her draw the conclusion that the sex of a fetus was determined by a chromosomal factor, and that ultimately males determine the gender of a baby. This discovery helped end the major scientific debate of if sex was due to heredity or embryonic environmental influence. Stevens continued to research and study different chromosome makeups of insects. She eventually discovered paired states of chromosomes in various flies and mosquitoes. Nettie Stevens had a lasting impact on biology and the study of genetics through her dedication and research.