N. M. (Nettie Maria) Stevens

Born in 1861, Nettie Maria Stevens was an American scientist whose research helped change how biologists understood heredity and sex determination. After studying at Stanford University, she carried out advanced research at Bryn Mawr College, where she focused on cytology and experimental biology.

Stevens is especially remembered for her studies of chromosomes in insects. In the early 1900s, she showed that sex could be linked to a specific difference in chromosomes, helping establish the role of what came to be known as the X and Y chromosomes. That discovery made her an important figure in the early history of genetics.

Although she died in 1912, Stevens is now widely recognized as a careful and original researcher whose work was ahead of its time. Her story is also a reminder of how often women scientists made major contributions even when they were given limited recognition during their lives.