The scientific journal Frontiers in Psychology has published research on feminism that is bound to be controversial. The study, published online September 9, proposes that feminist activists are masculinized women.

“Taking the psychology of sex-dimorphic traits and biomarkers into account, this theory makes very specific predictions. Using indicators of prenatal testosterone exposure, feminist activists should exhibit significant evidence of physiological masculinization when compared to a sample of women in general. The most widely used index of prenatal testosterone exposure is 2D:4D, the ratio of the length of the index finger to the ring finger,” Guy Madison of Umea University and his colleagues wrote in their study.

Researchers cannot directly measure prenatal testosterone levels in adults. But the difference between the length of the index finger and the length of the ring finger has been found to be a reliable indicator of prenatal testosterone levels. This ratio is known as 2D:4D — or second digit to fourth digit.

For their eyebrow-raising study, Madison and his colleagues measured the 2D:4D ratio of 35 attendees at a feminist conference in Sweden. The researchers also used a test known as the Ray Directiveness scale to measure personality traits related to social dominance.

Madison and his colleagues found that the average 2D:4D of the attendees was lower than usual for women but close to typical male values.

“In summary, the feminist activist sample had a significantly smaller (i.e., masculinized) 2D:4D ratio than the general female samples. The size of this difference corresponds approximately to a 30% difference in prenatal testosterone/estradiol ratio, which was the index found to have the strongest association with 2D:4D,” they explained.

The researchers also found higher than average ratings on the Ray Directiveness scale, suggesting the attendees were more socially dominant.

Madison and his colleagues said the findings don’t mean that every woman who calls herself a feminist was exposed to higher levels of testosterone in the womb.

“Moreover, the target population studied here is not necessarily representative for anyone who sympathizes with feminism or self-identifies as a feminist,” they wrote. “As our data pertain to feminist activists, we cannot and do not bring them to bear on women in general.”

“It would therefore be logically incorrect to infer that, for example, all feminist activists are masculinized or that all groups that are more masculinized are also feminist activists,” the researchers added. “On the contrary is it highly likely that professions and other activities that benefit from the practitioner being stronger, more aggressive and risk-taking, considered as more masculine traits, would also see a larger proportion of masculinized women among the more successful individuals.”

Madison and his colleagues claim the “feminists-as-masculinized-females theory” can help explain the so-called feminist paradox: why only a minority of women support a movement dedicated to improving their political rights and social position in society.

The researchers propose that the “activists who shape feminist attitudes and beliefs are themselves generally more physiologically and psychologically masculinized than is typical for women.”

“This might for example explain their belief in sex-role interchangeability, as they may perceive the behaviors and interests of sex-typical women as incomprehensible and at variance with their own more masculinized preferences in terms of child-rearing and status-seeking.”