Nettie Stevens: Chromosomes Determine Gender
In 1905, Nettie Stevens published a paper establishing that chromosomes, not environmental factors or diet, determine the sex of an organism. The same year, E.B. Wilson, a more celebrated male colleague, independently arrived at a similar conclusion and received most of the credit. She observed that male mealworms produced two kinds of sperm, one with a large chromosome and one with a small chromosome. Before this, there were many different theories as to how gender was determined during procreation. Aristotle believed a child’s sex was determined by the body temperature of the father during sex. “Aristotle counseled elderly men to conceive in the summer if they wished to have male heirs,” the textbook Developmental Biology explains. In 19th-century Europe, it was widely believed that nutrition was the key to gender determinants. Poor nutrition led to males, good nutrition to females.
Wilson was working on the same questions as Stevens, and he published a similar result around the same time. Wilson had worked on a species where the male actually has one less chromosome than the female, which is less common in nature. Stevens’s model of an X and Y chromosome is the basis for human gender determination. Plus, Stevens’s model better supports Mendel’s theory on genetics — that some genes take on dominant roles and override the instructions of their gene pairs. It is generally stated that E. B. Wilson obtained the same results as Stevens, at the same time. But Wilson probably did not arrive at his conclusion on this until after he had seen Stevens’ results. Because of Wilson’s more substantial contributions in other areas and sexism at the time, he tends to be given most of the credit for this discovery.