Among worms, there is equality.  When worms entwine, each could become a mother, a father, or both.  Neither worm has grounds to bemoan the fundamental unfairness of our universe – not while fooling around, at least.

Later, the worms might drown, or be eaten by birds, or be mutilated and held captive by a mole.  That all must feel horrible.  But while mating, each worm should feel as though it’s been given a fair deal.

Among emperor penguins, both parents make huge sacrifices for their young.  Each parent will huddle over the egg for months without food, staving off the Antarctic chill.  When it’s time to trade places, the parents must pass the egg using only their webbed feet – if they make even a small mistake, the egg will roll away and freeze, killing the chick inside.

Because each parent puts forth such a huge amount of effort to raise a chick, each must feel quite choosy during the mating season.  When a pair of penguins flirt, neither seems to have the upper hand.

Most animals’ reproduction is more asymmetric.  For them – for us – differing roles can feel unfair.

Often, one partner gets to be pickier than the other. 

Among smooth guardian frogs, fathers are deeply invested in raising their young; mothers hop away after mating, providing no help.  Female smooth guardian frogs seem as though they’d be perfectly happy to make babies with anyone.  They can always have another fling while a past paramour is protecting the last batch of eggs.

For a male, mating is a serious commitment.  He’ll carefully consider his options. And so each female sings to woo him.  A common strategy: knowing that males are choosier when it comes to sex, she’ll sing her heart out, hoping to sway his decision.

Among many other species of frogs, males’ songs serve the same purpose.  Hoping to woo womenfolk, male bowerbirds build.

Female ducks raise their young.  They have the freedom to choose their mates.  Male ducks would have more leverage during courtship if they planned to contribute as parents.  But they don’t.

Male ducks are the natural world’s equivalent of violent incels.  Aggrieved by their lack of choice, they rape.  This has been going on so long that female ducks’ anatomy has evolved – they can trap unwanted sperm with labyrinth passageways inside their bodies, and are able to straighten the path to fertilization during consensual sex – allowing them to maintain mate choice despite the constant threat of assault.

From an evolutionary perspective, animals that put forth an effort as parents have earned their choices.  They generally get to indulge their desires … and, even more importantly, should be safe from those whom they do not desire.

Among many species, we can see evidence of this push and pull between devoted parents and the absentees who loudly sing, “Choose me!  Choose me!”

For instance, we can learn a lot about the sex lives of our closest relatives by comparing the males’ genitalia.  No, not your uncle – that’d be weird.  I mean the great apes.  A traditional comparison of gorillas, chimpanzees, and humans is shown below.

Male gorillas claim a territory, and then the dominant male within each territory feels reasonably certain that every female living there will mate with him and only him.  Although he makes minimal contributions toward parenting – which means the females should feel free to shop around for sexual partners – he sways their decision through physical violence.  Mostly he’ll direct aggression at other males, hoping to stave off their competition, but he’s occasionally rough with “his” females as well.

For male gorillas to control female sexuality without helping as parents, they had to become huge.  As it happens, this evolutionary pressure caused their brains to shrink.  They have almost 90% fewer neurons than we’d expect for a primate of that size.  If gorillas were egalitarian, they would’ve been more intelligent than humans.  But there simply weren’t enough calories for gorillas to have large brains and sufficient brawn to indulge in violent sexual coercion.

Image by Ryan Poplin on Flickr.

There’s less difference in size between male and female chimpanzees, but male chimpanzees also use violence to sway mate choice.  A male chimpanzee might attack and kill a mother’s babies in order to impregnate her … but he won’t if he thinks that they might be his own children. 

The safest plan for a mother, then, is to distribute her sexual favors widely.  Her children will safe from everyone with whom she shared a dalliance.  Maybe she’d like to be choosier, but each male will only last a few seconds, so the cost must not seem like too much to bear.

From an evolutionary perspective, then, male chimpanzees are not competing to be the most beautiful.  Nor to be the greatest artists.   They don’t sing.  They do battle, but they tend to battle in cooperative gangs, with the outcome being that each male among the upper echelon will have the chance to get it on.   A friendless, low-ranking male might be chased off every time he attempts to mate, but many others will have an occasional opportunity.

That’s why male chimpanzees produce so much sperm.  The chance to fertilize a mother’s egg comes down to probability.  If a chimp ejaculates prodigiously, he’s more likely to sire offspring.

Several human cultures believed that babies are formed from sperm, and that mothers required repeated infusions during pregnancy in order for the child to form correctly.  Among the Bari of Venezuela, each man who contributed sperm was treated as a biological father – the child was presumed to inherit virtues from each.

Under these beliefs, polyamory was the best strategy for raising a capable child.  A mother needed to consider which qualities would help her children most in life, then spend time astride the men who possessed each.  The best singer, the most nimble climber, the most astute tracker – each trait was an evening’s lay away.

And her strategy surely worked.  Fooling around with the best singer would probably lead to singing lessons.  If the best hunter also shared an orgasm with this child’s mother, he’d make an effort to explain the sights and sounds and rhythms of the forest.  Honestly, it makes no difference whether talents come from nature or nurture if fathers are willing to teach every child that their sperm might’ve helped create.

The Bari culture, like that of most other human hunter gatherers, was quite egalitarian compared to our own.  But even among hunter gatherers, human fathers were typically shabbier parents than mothers.  For instance, fathers who hunted typically claimed to be the ones feeding their families, even in places where the “women’s work” of gathering fruits, nuts and seeds provided more nutrition than meat.  But an occasional dead deer confers more bragging rights than a sackful of nuts each day, and human males have long loved to brag.

As humans began to practice agriculture, our societies became less equitable.  More and more of the childrearing was done by women.

According to the basic principles of evolution, this means that women should have had more and more leverage during courtship.  More and more control over their sexuality.  In cultures where mothers do basically everything – feeding the family, teaching children, cuddling them through the night – women should have had close to free reign in choosing their partners.

And there’s biological evidence that human women used to be in control.  For instance, many women’s sexual preferences seem to cycle rhythmically.  Relatively effeminate, helpful partners are favored most of the time, but ultra-masculine brutes suddenly seem sexy during temporary bursts of hormones.  In the past, human women probably made out with multiple different men each year.

That’s why human males – unlike gorillas or chimpanzees – have a strong incentive to provide a rollicking good time in bed.  Or in the back of a cave, on the forest floor, alongside the riverbank, wherever.  Although there’s been intense debate about the degree of correlation between male penis size and female sexual pleasure, most people seem willing to admit that there’s a link.

When women buy sex toys … well, usually they buy external vibrators.  These don’t always resemble the genitalia of any biological organism.  Many are designed to look like lipstick tubes or other innocuous objects, for modesty’s sake.

But toys that are designed for penetration?  These tend to be much longer and thicker than either a gorilla’s inch-long erection or a chimpanzee’s three-inch, slender shaft.  Human males tend to be well endowed because it’s a way to sway women’s choices.  By giving her a good time, a man might have the chance to fool around again.

But in addition to huge cocks (relative to other primates – as Jeffrey Yang wrote in his poetry collection An Aquarium: The barnacle has the longest penis / of any animal in proportion / to its body size.  Happiness / and proportion: / never be ashamed of evolution), humans also have huge brains.  Instead of evolving better and better ways to deliver consensual pleasure, human males invented stories to subvert female mate choice.

Human males aren’t as horrible as ducks, but we’re close.

Around the world, human males have used religion as a tool to constrain female choice.  We teach that the natural inclination toward polyamory is evil.  A woman needs to devote herself to one man.  In many cultures, women are not even allowed to choose who that man will be.

Even in contemporary experiments on U.S. college students, the presence of sexual competitors leads people to espouse more strident religious experiments.  If you can’t win with your looks, or with your charming personality, why not tell her that it’d be immoral to make eyes at that other guy?

Human men could have made art like bowerbirds.  We could’ve sung like frogs.  Hell, we could’ve capitalized on the promise of our large genitalia to deliver such sweating shaking shuddering good fun that our sexual partners would remain dazzled forever.

Instead, we invented deities, spirits, and purity laws.  We taught that women who dallied should be stigmatized, or stoned, or murdered by God with a rain of burning sulfur.

If emperor penguins learned about our sex lives, they’d be appalled.  “Dude,” a penguin father might say, “you don’t need to coerce her with a sky ghost!  Just be a good parent.  Then you’ll get to choose, too.”

That’s sound advice, Mr. Penguin.  I am trying to be a good parent.  Even when the kids are fussing, I try.

Featured image by Property#1 on Flickr.