Gay hands

Yet it made headlines anyway, because it fit a narrative some people wanted to believe.

The hunt for the gay gene didn't stop there. Far from it. Between weeks 8 and 14, tiny fetal testes, ovaries and adrenal glands secrete the baby's own supply of sex hormones. It wasn’t.

This finger-length study was just one part of a frenzied hunt for the elusive "gay gene." But why were scientists so desperate to find a biological basis for homosexuality?

Studies indicate genes wield much influence.

Even as digit ratio research flourishes and more behavioral links are established, the relationships will remain mere statistical correlations until researchers fully understand how sex hormones physically affect the brain. Fingers are an indication of the environment that molded the brain, but only if you know how you measure up to others.

"You have to be careful," he says.

The same study, published in Early Human Development, found that boys with female-type finger lengths are on average more emotional than other boys. Or wrong? Other sexually dimorphic traits, such as height and waist-to-hip ratio, don't appear until puberty.

"Everything you see as far as sex differences in the behavior of toddlers is an aftereffect of prenatal testosterone," says Dennis McFadden, a psychology professor at the University of Texas at Austin.

It was a scientific merry-go-round, with each new study contradicting the last.

The truth is, human sexuality is insanely complex. That finger study? But we need to approach "groundbreaking" studies on controversial topics with a healthy dose of skepticism, especially when they perfectly align with a political narrative.

True science is messy.

Lesbians are more likely than straight women to have a masculine finger ratio, says McFadden.

The data in men, however, are more complicated and contradictory. It was politics.

The gay rights movement was gaining significant momentum in the '80s. For decades, scientists chased various leads: hormones, brain scans, birth order - you name it, they studied it.

Many scientists believe relative finger length—or digit ratio—is a marker for brain differences molded by hormones. Like a bit of prenatal graffiti, a longer ring finger says, "Testosterone was here."

John Manning, a biologist at the University of Liverpool, first identified digit length as a sign of prenatal hormones eight years ago.

In women, these fingers are usually the same length or the index digit is just a bit longer.

Digits are subtly affected by testosterone and estrogen produced in the womb by the fetus (not by the mother). Likewise, males with a typically female ratio exhibit more typically feminine behaviors.

A study of digit ratio in Scottish preschool children between the ages of 2 and 4 found strong relationships between digit ratio and gender-normative behavior.

"You can't look at someone's fingers and make a determination about whether they are heterosexual or lesbian, just as you can't decide whether they're neurotic. The [sexuality indicators] are most certainly there, but they're not strong enough to allow us to make predictions."