Project Results

Romantic and sexual orientation are considered key parts of one’s identity. But are they so much a part of one’s “identity” as part of one’s hormonal make-up? By using a biological marker for testosterone and estrogen levels, the ratio of index finger (second digit) to ring finger (fourth digit) length (aka 2D:4D), it was investigated whether hormonal balances influence romantic and sexual preferences - similar to many studies before it (Manning and Robinson, 2000; Manning and Robinson, 2003; Manning, Churchill, and Peters, 2007) - but differing in the critical aspects of looking not only into sexual preference but romantic preference as well, and taking into account the transgender and transsexual populace. For centuries, there has been research into the causes of homosexuality. But it’s been cisnormative, and didn’t view romantic and sexual orientation as separate entities. The findings of this study show that in fact, hormonal balances have a significant influence on sexual orientation in birth-males regardless of race or ethnicity (the effects of which were insignificant). However, 2D:4D is only a significant indicator of romantic orientation for birth-males in the right hand. In birth-females, the direction of the correlations between 2D:4D ratio and romantic and sexual orientation supported the same conclusion (that hormonal balances play a role in orientation); however, unlike with males, they were insignificant.

A notable secondary finding was that a participant’s sexual orientation significantly predicted romantic orientation regardless of birth sex. It was also found that there was a significant positive correlation between the degree of homosexuality or homoromanticness and one’s tendency to be polyamorous. Finally, it was observed that out of all combinations of sexual and romantic orientation, bisexual biromantics were most likely to be attracted to non-binary individuals (whether transgender, transsexual, genderfluid, or intersex).

Video summary: https://youtu.be/MVGoJincQL4 

About This Project

The ratio between one's index (2D) and ring finger (4D) is an indicator of prenatal androgen balances, which in turn have a permanent effect on adult hormonal balances. I hypothesize that for birth-males a preference for men, whether sexual or romantic, will increase with 2D:4D ratio, whether for the left or right hand. For birth-females, a preference for women, whether sexual or romantic, will decrease with 2D:4D ratio, whether for the left or right hand.

Ask the Scientists

What is the context of this research?

I was inspired to start this project when my friend came out to me, and we both wondered: why are we the way we are? After some digging, I uncovered a theory that intrigued the both of us. What if your prenatal hormonal balances, shown through your index to ring finger length (2D:4D) ratio, have an effect on your preferences as an adult? What perturbed us, however, was that the transgender and transsexual communities had been overlooked in these studies, which could seriously impact the reliability of results (explaining why many studies reported different findings). Not only this, but romantic orientation and it's relation to 2D:4D ratio, had never been investigated - only sexual orientation. Last but not least, asexuality and aromanticness had never been included either.

What is the significance of this project?

This division within the psychological community as to whether orientation is acquired or inherent, and the outdatedness, bias, discordance, and general unreliability in much of the research that exists, is why it is our responsibility to utilize the large LGBT community and ethnic diversity within New York City to gain indisputable insight into this topic. This survey will encompass groups that hadn’t been accounted for in the past, such as transexuals, transgenders, intersexuals, and those with differing romantic preferences to their sexual preferences, as well as take into consideration each participant’s detailed ethnic origin rather than simply their nationality. We will see, through this study, if 2D:4D is likely connected to sexual and/or romantic orientation.

What are the goals of the project?

My hypothesis is that prenatal hormone proportions (displayed through 2D:4D ratio) affect sexual and romantic orientation. To test this hypothesis I'll survey 1000 participants (500 online on SurveyMonkey and 500 on the street). Participants are eligible if they're aware of their sexual and romantic preferences, and have never injured at least one of their hands. I'll measure the index and ring finger lengths of each participant, and ask them a series of questions about their birth sex, current gender, current sex, race and ethnicity (to control for racial variations), height and weight (to control for finger thickness), and romantic and sexual orientation. With this data I'll see if 2D:4D has a significant correlation with orientation.