The annals of science journalism weren’t always as inclusive as they could have been. So PopSci is working to correct the record with In Hindsight, a series profiling some of the figures whose contributions we missed. Read their stories and explore the rest of our 150th anniversary coverage here

Imagine a world where your sex cells determine your entire personality. If you have vigorous little sperm wriggling around your testes, you too must be energetic and raring to achieve. Carry a delicate basket of large, motionless eggs, and you’re probably more an inert, submissive type—waiting for life to happen to you.

Were it not for the work of psychologist Helen Thompson Woolley, some version of such a presumptive existence—the one into which she was born in 1874—might still exist. Throughout the Western world of the late 19th century, men enjoyed active participation in all aspects of civil and intellectual life, while women were expected to confine their attention to domestic matters. The thinking of the day was codified in The Evolution of Sex, a tome published two male scientists: John Arthur Thomson, a naturalist, and Patrick Geddes, a biologist. Comparing humans to cochineal insects, threadworms, and some parasites—species in which the females are rather motionless egg-carriers—they concluded that across life, “on an average the females incline to passivity, the males to activity.” (That book was praised as “splendid” in a 1911 Popular Science essay titled “The Constitutional Conservatism of Women.”)

Fortunately, Woolley, born in Chicago, Ill., had other ideas. Her family encouraged her education, and she, like many others during the so-called Progressive Era, developed a conviction that science could solve social ills. In 1893, thanks to a scholarship, she enrolled at the newly founded University of Chicago, where she gravitated toward the burgeoning field of experimental psychology. A graduate fellowship set the stage for her dissertation, The Mental Traits of Sex: An experimental investigation of the normal mind in men and women, published as a monograph in 1903. The goal of her research was straightforward: to be the first to “obtain a complete and systematic statement of the psychological likenesses and differences of the sexes by the experimental method.” In saying so, she boldly implied that the perspectives of respected scientists like Geddes and Thomson had no empirical basis.

In her experiments, Woolley put 25 female and 25 male university students through a range of tests to measure characteristics like motor skills, sensory abilities, intellectual capacity, memory, and personality. Slight differences emerged: Men performed better on most tests of motor skills, while women had superior sensory discrimination. But these observations were outliers. “In essence,” says York University psychology professor and feminist scholar Alexandra Rutherford, Woolley found that “women and men were more the same than different.” What’s more, Woolley’s conclusion stated that “The biological theory of psychological differences of sex is not in a condition to compel assent.” 

Biology alone couldn’t account for differences between men and women, she argued. The way they were raised and treated had to be considered, too. Boys, for example, were encouraged to exercise and play, while girls were kept at home and discouraged from activities that weren’t deemed “lady-like.” No wonder they scored differently on physical tests, she wrote. Though such conclusions may seem obvious now, they directly challenged the “rampant biological essentialism of her time,” says Rutherford. 

Woolley’s dissertation, according to Rutherford, received mixed reviews. While some found it compelling and important, other critics complained that the women in her study could attend college and therefore were the “cream of the crop” and hence weren’t a fair comparison for average college-educated men. Remarks of this nature indicate the intellectual environment Woolley was up against, which also helps explain why it took so long for her ideas to take hold. Nearly a decade after she published her findings, in her 1910 review of the research on sex differences, she noted that literature was “improving in tone” but was still rife with so much personal bias, prejudice, and “sentimental rot and drivel” that it could hardly be considered scientific.

Today, our understanding of humanity is changing to embrace a spectrum of biological sexes beyond the binary of Woolley’s day. Psychologists understand that sex is separate from gender, and there are a number of ways in which the two can intersect. Equality has yet to be achieved across those identities, but science and society have come a long way from expecting people to behave like sperm and eggs. 

The conversation that Woolley’s work sparked, however, is still ongoing. Throughout some areas of science, the notion that there are biologically ingrained psychological differences between males and females is still prevalent. These assumptions continue to shape cultural expectations of how people should behave and what they are capable of achieving. Women are underrepresented in academic fields typically thought to require raw intellectual talent, and social stereotypes lead children as young as six to believe that girls are less interested than boys in computer science and engineering.

In the 2011 book Brain Storm, the scientist and gender studies scholar Rebecca Jordan-Young challenged the notion that sex differences existed in the brain, echoing Woolley in her argument that “brain organization theory is little more than an elaboration of longstanding folk tales about antagonistic male and female essences.” Over a century ago, Woolley showed that these stories were hopelessly out of date—and that the only way forward was to rewrite them.