12.3: Scientist Spotlight - Nettie Stevens

Last updated
Save as PDF

Page ID: 132407

\( \newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \) \( \newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash {#1}}} \)\(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\) \(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\)\(\newcommand{\AA}{\unicode[.8,0]{x212B}}\)

Famously, King Henry VIII had six wives in his efforts to have a male heir. He disposed of each for various acts of disrespect, but most especially, for not providing him a son. Throughout history, the birth of a female child, over the oft-preferred male child, has lain with the attitudes or defiance of women. Aptly, it would be a woman to discover the determining factor of sex at birth and free the future of women from such accusations. Within the scientific community, sex had been long-debated as either an inherited trait or one influenced by embryonic environmental influence, and it was ultimately Dr. Nettie Stevens who uncovered the truth.

Figure \(\PageIndex{1}\): Photograph of Nettie Stevens, taken at Carnegie Institution of Washington and kept in the Bryn Mawr College Photo Archives. Image available in the public domain.

Stevens was a native of Vermont, born in 1861 and dying at the age of 51 in 1912. She studied biology at Westfield State College, where she was only one of three women to graduate between 1872 and 1883. After a few years of teaching, she went on to earn an MA at Stanford University and a PhD at Bryn Mawr College. In the early 1900s, she shifted her research from morphology to cytology and regeneration, leading her to the topic of embryo and chromosome variations. By 1905, she published her findings on yellow mealworms (Tenebrio molitor) and the X and Y chromosomes as the cause of an individual’s sex at birth. Two X chromosomes (XX) results in a female, while one of each (XY) results in a male. It is now known that the first X is inherited from the egg, while the second (either X or Y) is inherited from the sperm. In her paper, Stevens concluded, “this seems to be a clear case of sex-determination…by a definite difference in the character of the elements of one pair of chromosomes…, the spermatozoa which contain the small chromosome determining the male sex, while those that contain 10 chromosomes of equal size determining the female sex” (1905, p. 13). Not only did Stevens’ discovery resolve the debate surrounding sex origins, it was the first time that scientists could link a phenotype to a specific chromosome. Stevens’ reputation and contributions to the field of genetics are often overlooked by subsequent findings on the topic during the same time period, with more credit given to her male contemporary Dr. Edmund Wilson, but the value of her discoveries have been incalculable.

Figure \(\PageIndex{2}\): Title page of Nettie Stevens academic paper, outlining her research and her findings on the genetics of assigned birth sex.

Figure \(\PageIndex{3}\): Carl Zeiss Jena 8261 Microscope used by Nettie Maria Stevens. This image was provided to Wikimedia Commons by Bryn Mawr College as part of a cooperation project (licensed under CC BY-SA 3.0).

As culture continues to evolve, modern scientists now know that there are more than the simple XX and XY, male and female binary, that Stevens had originally written about. Today, our concepts of sex pertain to the biological sense which Stevens focused on, though intersex has been added to the male or female classifications and we recognize in the present day that assigned birth at sex does not necessarily indicate gender identity. With science as an accumulated field, guided by the culture it exists within, our concepts of sex and gender will continue to adjust with time, using foundational knowledge like that afforded to us by Dr. Nettie Stevens as a stabilizer for the heights we will reach.

References

Brush, S.G. (1978). Nettie M. Stevens and the discovery of sex determination by chromosomes. The University of Chicago Press, 69(2), pp.162-172. https://www.jstor.org/stable/230427.

The Editors of Encyclopaedia Britannica. (n.d.). Henry VIII. Britannica. https://www.britannica.com/biography/Henry-VIII-king-of-England. Accessed 1/26/2024.

The Editors of Encyclopaedia Britannica. (n.d.). Nettie Stevens. Britannica. https://www.britannica.com/biography/Nettie-Stevens. Accessed 1/26/2024.

Stevens, N.M. (1905). Studies in spermatogenesis. Carnegie Institution of Washington, 36, pp. 33-74.