August 2016 Articles

Final Word: The Theory of Inheritance

Final Word_Nettie_Stevens_microscope-2In Biology Professor Gregory Davis’s class The Historical Roots of Women in Genetics and Embryology, students are introduced to the women who contributed to the field of genetics and developmental biology. One of them, Nettie Maria Stevens, has a special place in students’ hearts. A Mawrter herself—she earned her Ph.D. in 1903—Stevens also worked at Bryn Mawr as a researcher and made one of the landmark breakthroughs in the history of genetics: the chromosomal theory of inheritance.

One of the first women to make a name for herself as a biologist, Stevens graduated first in her class at Westfield Normal School in Vermont. After a stint as a high school teacher and librarian, she headed west to Stanford, where she became interested in cytology. From there, she came to Bryn Mawr for graduate work in the lab of future Nobel laureate Thomas Hunt Morgan.

Nettie_StevensIn Morgan’s lab, she marshaled evidence that the particular combination of X and Y chromosomes determined an individual’s sex. Her 1905 paper Studies in Spermatogenesis upended the then-prevailing view that factors in the embryo’s environment—temperature and nutrition—determined its sex.

At Bryn Mawr, she received a prestigious President’s European Fellowship, which sent her to the Zoological Institute at Wurzburg, and as a post-doc, she spent a year at the Carnegie Institute of Washington. But Stevens spent most of her career at Bryn Mawr and most of that in the biology lab. She was poised for a research professorship at Bryn Mawr but died, from breast cancer, before she could step into the position.

Final Word_BW2Her memory survives on campus—and online. Special Collections inherited her then-state-of-the-art Carl Zeiss Jena 8261 microscope, and this spring, students in Davis’ class used it to study aphid oocytes—among the same organisms that Stevens herself studied.

Online, Stevens was honored when she appeared as the July 7 Google Doodle on what would have been her 155th birthday.