Our American mass shootings are misunderstood as a mental-health concern, and the toxic masculinity that compels many shooters isn’t anything so simple as longstanding socialized behavior rendered recently abhorrent. Male fragility is a biological fact, encoded in our cells. This certainty has yet to work its way into our popular consciousness, but the body of evidence is now irrefutable. Each lone gunman—engaging, by the week, in blatant acts of domestic terrorism, eroding the safety of our schools, dance clubs, and churches—shows us the same damn thing. These killers of women and children, of teachers and deacons, are often white but not always, often young but not always, often certifiably sane but not always. But be he a Nikolas Cruz or a Stephen Paddock, a Dylann Roof or an Omar Mateen, the killer is always, always a man.

As with the science supporting climate change, confirmation of masculine weakness is capable of inspiring stubborn cases of denial.

Scientists and sociologists have known for decades that boys are fairer than girls, and by far. As with the science supporting climate change, confirmation of masculine weakness is capable of inspiring stubborn cases of denial. The stereotypical softness we’ve historically imagined is the birthright of being born a girl? Well, in reality these misattributed frailties are the quantifiable traits of boyhood.

Boys are less hearty in vitro, suffering higher miscarriage rates, along with higher mortality into infancy and on through to old age (save for a year or two around age ten, when U.S. mortality rates break about evenly). In the 1750s on, U.S. records show, baby boys died at a rate 10 percent higher than girls. Come the 1970s, the gap opened to more than 30 percent. Today it stands around 20 percent. Boys are more sensitive than girls. Boys do cry more, are more anxious, have a harder time regulating emotion, care less about objects in their environment, are more likely to suffer developmental disorders and genetic defects, and are more susceptible to malnutrition and disease. For boys, parental unavailability and insensitivity have a greater effect on attachment to a caregiver. The irony here is that, via our impressive human prejudice, we’ve transposed nearly every imagined indicator of gender-inflected weakness from boys to girls. Without knowing it, we have for ages wanted our girls to be more like boys and our boys to be more like girls.

All in all, boys are less developed than girls—physically, emotionally, intellectually—until late adolescence. By then, the turns and twists of our painstaking mammalian maturation have often made masculine developmental deficiencies lifelong traits. Still, this doesn’t mean that the deficiencies must necessarily translate into detriments—this transmutation had been the handiwork of patriarchal culture.

Human history, and its eons-long expression of patriarchal domination, is evidence that certain deficiencies lead to significant advantage. Is it any wonder that men commit more suicides and murders? In the United States, the male-to-female suicide death ratio hovers around 3.5:1 (this despite women attempting twice as many suicides as men). The U.S. male-to-female murder ratio remains constant even as the total numbers dropped over the years, at about 9:1. Homicide and suicide arguably are, in Western culture, our greatest expressions of emotional weakness.

The inaccurate stereotype of female passivity looks like a learned coping strategy resulting from the anxiety and instability in the fairer (yet more muscular) sex.

This constitutive gender gap isn’t a recent sociological phenomenon; it’s an antediluvian evolutionary absolute. To grasp just how ancient the male penchant for emotional weakness is, consider one of our close cousins, the rhesus monkey. When deprived of maternal care, rhesus males freeze more frequently in stressful test situations than females, who prove to be more curious and more active. Our science shows that female passivity isn’t biological; it isn’t even passivity. In the bold face of swelling evidence, the inaccurate stereotype of female passivity looks like a learned coping strategy employed against ages of oppression resulting from the anxiety and instability in the fairer (yet more muscular) sex.

Despite manifold physical advantages, women still face greater socioeconomic disadvantage than men, but here in the United States, at least, these enforced disadvantages are diminishing, and have even become demonstrations of female socio-physical advantage, in spheres ranging from education to health to employment. For a century and a half, women have held the lead in longevity. This longstanding marker of female fitness in the industrialized world must no longer be attributed to greater male proclivities toward risk-taking and work-related deaths.

Girls are—simply and truly—heartier than boys by just about every measure, and any self-respecting Darwinian—no longer exclusively a men’s club—would agree that women are the fitter sex. This doesn’t hold true for humans alone. Females of most species live longer lives, suggesting that the innate strength and resilience of females lie buried in biology.

The reason for greater female fitness is due to the discovery that women are less disposable. “In humans, as in most animal species, the state of the female body is very important for the success of reproduction,” writes Thomas Kirkwood, who in the 1970s proposed the theory of the disposable soma. “The fetus needs to grow inside the mother’s womb, and the infant needs to suckle at her breast. So if the female animal’s body is too much weakened by damage, there is a real threat to her chances of making healthy offspring.” As a result, on a cellular level, females show enhanced regenerative ability. The male reproductive role isn’t as contingent upon a father’s continued good health, and so ruthless evolutionary efficiency has determined that the male body is less essential.

If we as a culture were more capable of facing the plain truth that our girls and women possess a superior fitness, we might all feel less inferior.

Which is not to say that for all our mortal genes care, a man may perish moments after consummation. In studies of isolated populations, children who lose fathers during childhood tend to be somewhat shorter than their peers. More tellingly, though, motherless children are far shorter, poorer, and die sooner than children without fathers.

Results from rodent tests suggest that the female body heals better than the male body. But once a rat’s ovaries are removed, this regenerative power likewise vanishes, eliminating entirely any health benefits. Further demonstrating this sex-organ imbalance—ovaries extend life, testes truncate life—neutered male dogs and cats live longer, on average, than their betesticled cohort.

Though the samples are small and come from a period in human history when data were scant, testicularly intact men die earlier than eunuchs. Cross-dressing Shakespeare, as with most things, was ahead of his time when he wrote the eunuch Charmion’s suggestive retort to the soothsayer in Antony and Cleopatra: “Oh, excellent! I love long life better than figs.” If we as a culture were more capable of facing the plain truth that our girls and women possess a superior fitness, we might all feel less inferior. And a wider cultural acceptance of male fragility may one day lead our boys and men to better know that the most difficult expression of masculine strength is not the determined use of deadly force. It’s knowing when and how to ask for help.