A new study from Brazil has uncovered differences in adult hormone levels between subgroups of lesbian women and heterosexual women. The research, published in Adaptive Human Behavior and Physiology, found that lesbian women who described themselves as having a more masculine style had higher levels of free testosterone in their saliva compared to both feminine lesbian women and heterosexual women. At the same time, the study did not find differences in the ratio of the lengths of the index finger to the ring finger—a measurement thought to reflect early hormone exposure—across these groups.
Previous studies have suggested that the amount of certain hormones, such as testosterone, during early development may help shape the brain in ways that could influence sexual attraction later in life. Other work has noted that testosterone in adulthood can vary among women and might be associated with differences in behavior or self-expression.
However, earlier research has often treated lesbian women as a single, undifferentiated group, even though some identify with a more masculine style while others lean toward a feminine presentation. The new study was designed to explore whether there are biological differences in adult hormone levels and in a marker that is believed to indicate exposure to hormones before birth between these groups.
To investigate these questions, the research team conducted their study in the metropolitan area of Belém, the capital of the state of Pará in Brazil, between 2013 and 2015. The participants were women between 18 and 39 years old who were in their reproductive years. The study carefully selected women who either identified as exclusively heterosexual or predominantly or exclusively homosexual.
The researchers also asked the participants to rate their own level of masculinity or femininity based on how they saw their behavior, style, and self-expression. Women who rated themselves on the lower end of a nine-point scale were categorized as having a more feminine style, while those who rated themselves on the higher end were considered to have a more masculine style. This approach allowed the study to compare not only heterosexual women with lesbian women in general but also to compare lesbian women who describe themselves as more masculine with those who describe themselves as more feminine.
To assess prenatal testosterone exposure, the researchers used the well-established method of measuring the 2D:4D finger length ratio. This involved using a caliper to precisely measure the length of the index finger (2nd digit) and the ring finger (4th digit) on both hands. The ratio was then calculated by dividing the index finger length by the ring finger length. Lower ratios are generally associated with higher prenatal testosterone exposure.
To measure current testosterone levels, saliva samples were collected from a subset of the participants. The researchers took care to control for potential fluctuations in testosterone levels due to the menstrual cycle by collecting samples only during a specific window of time (days 23-27). They also provided participants with instructions to avoid factors that could influence testosterone levels, such as alcohol consumption and strenuous activity, in the 24 hours prior to sample collection.
The findings of the study were clear in some respects and less so in others. When the researchers looked at the finger ratio, they did not find significant differences between heterosexual women, feminine lesbian women, and masculine lesbian women. This result suggests that the marker thought to reflect hormone exposure during fetal development did not vary in the way that some theories had predicted.
On the other hand, when the team examined free testosterone levels in saliva, they observed that lesbian women who identified as more masculine had higher testosterone levels than both their feminine lesbian counterparts and heterosexual women. In contrast, the testosterone levels in feminine lesbian women and heterosexual women did not differ significantly from one another. In addition, the researchers did not find a link between the finger ratio and the testosterone levels in saliva, meaning that these two measures did not seem to be related in the sample examined.
The results support the idea that adult hormone levels may be linked to the behavioral and self-presentation differences observed within the lesbian community. Although testosterone levels in adulthood are not thought to cause sexual orientation, the differences in hormone levels may help explain why some lesbian women have a more masculine or butch style while others have a more feminine or femme style. This finding adds to previous research that has hinted at a biological underpinning for the differences seen among lesbian women.
But the study has some limitations that need to be considered. First, the sample size, especially for the masculine lesbian group, was relatively small. This could have limited the study’s ability to detect subtle differences in the 2D:4D ratio. A larger sample size might reveal different results. The research team also noted that using a convenience sample might not fully represent the broader population of women. There were challenges in recruiting participants, and some potential participants dropped out at various stages of the study, partly because of discomfort with aspects of the data collection process.
Looking ahead, the researchers suggest that further studies should include a larger number of participants to improve the ability to detect smaller differences, particularly in measures that might indicate early hormone exposure. Future work might also benefit from using additional or alternative methods to measure hormones in the body, and from screening participants for other health conditions that could affect hormone levels.
Despite these limitations, the current study suggests that there are measurable biological differences between subgroups of lesbian women, specifically in terms of adult testosterone levels. This highlights the importance of recognizing the diversity within the lesbian community and not treating it as a single, homogenous group.
The study, “Testosterone Concentrations and 2D:4D Digit Ratio in Heterosexual and Masculine and Feminine Lesbian Women,” was authored by Vivianni Veloso, Ana Catarina Miranda, Cibele Nazaré Câmara Rodrigues, Nelson Corrêa Medrado, Maria Cecília Silva Nunes, Mauro Dias Silva Júnior, and Marie Odile Monier Chelini.
