Atikh Bana/Unsplash

It has something to do with winter births.

Eighty-five percent of all humans identify as right-handed — and the world is built to accommodate this supermajority. Lefties suffer the indignities of using desks, scissors and baseball gloves that are specially constructed for people with a completely different dominant side. Even language persecutes southpaws — in Latin, the word “left” is translated as “sinister.” The French word for left is “gauche,” meaning awkward.

Men are 23% more likely to be left-handed than women, but cultures and religions throughout history have linked the left side of the body with femininity. For example, South African tribes consider the right hand to be the “male hand” and the left to be the “female hand.” There are similar associations in Hinduism, Hatha Yoga, Jewish mysticism, Celtic and ancient Greek cultures and even Christianity.

Science has traced our predisposition to right-handedness back thousands of years. “There has never been any report of a human population in which left-handed individuals predominate,” writes Natalie Uomini, an archaeologist at the University of Liverpool, in a 2009 study published in the Journal of Human Evolution.

A combination of genetic and environmental factors explains why people prefer to use their left hand (or left foot). But why are there more left-handed men than there are left-handed women? What kind of gendered bullshit is this?

Let’s investigate.

The fighting hypothesis

The strongest explanation for why there are more left-handed men than women comes to us courtesy of researchers in France. Charlotte Faurie and Michel Raymond of the University of Montpellier theorize that being left-handed gives boxers an “infrequency advantage” — left-handed fighters often practice against right-handed opponents, but right-handed boxers have fewer opportunities to practice against lefties. The result of this is that left-handed boxers have a fundamental advantage in the ring.

In 2004, the researchers visited nine undeveloped societies to test their theory that left-handed people are more successful fighters than righties. Their study confirmed that there are more left-handed people in societies with high levels of violence. This partly explains why handedness is a gendered issue — historically speaking, men resort to violence more often than women do, so it’s evolutionarily beneficial for men to have a dominant left side.

Left-handedness and hormone levels

Left-handedness among men has also been linked to their hormone levels — a 2014 study out of the University of Vienna speculates that men born in the winter are more likely to be left-handed because daylight increases testosterone levels.

Let me explain: Winter babies develop primarily during the spring and summer, when there’s a lot of sunlight. As a result, the fetuses’ increased levels of testosterone can “delay the maturation of the left brain hemisphere during embryonic development,” meaning that the more testosterone a fetus has, the weaker their left-brain hemisphere may be. And since the left-brain controls the right side of the body, male babies born in winter are more likely to be left-handed.

Other studies speculate that testosterone affects left-handedness in different ways. A 2001 study published in the Archives of Sexual Behavior suggests that people with a gender identity different from the one that was assigned to them at birth are more often left-handed, owing, in part, to increased levels of testosterone during their fetal development.

There’s no shortage of studies on lefties; scientists have attempted to link left-handedness with paraphiliacs (people with sexual fetishes or who identify as having non-normative sexual identities) and homosexuality (studies performed in 2000, 2002 and 2003 all provide conflicting evidence).

Regardless of how or why lefties came into being, they’re in good company — four of the last five United States presidents identify as southpaws.