N. M. (Nettie Maria) Stevens

Born in Cavendish, Vermont, in 1861, she began her professional life as a teacher before turning to science more fully as an adult. She studied at Stanford University and later at Bryn Mawr College, where she worked in cytology and embryology at a time when women had few paths into research.

She is best known for her 1905 work on insects, especially mealworms, which showed that sex is linked to different chromosome combinations. That finding helped establish the chromosome basis of heredity and made her one of the key early figures in genetics.

Her life was brief—she died in 1912—but her influence has lasted. Today she is remembered as a careful, original scientist whose work clarified one of biology’s central questions and opened the way for later genetic research.