Female Promiscuity Controls the Size of Your Testicles

Psychics gaze into crystal balls and tell you vague things about your future. Biologists gaze at your actual balls and tell you precise things about the scandalous behavior of women in our ancestral past.

Breeding experiments with sheep and mice have illustrated the testicle phenomenon swimmingly. Over the generations, monogamous female mice and sheep have little effect on the size of the males’ gonads. But female mice and sheep who are monogamous in public—but promiscuous in secret—quickly cause the evolution of larger gonads in the males.

Let’s take a close-up look at your testicles.

First let’s measure output. This is no time for squeamishness. When it comes to male ejaculations, biologists take a hands-on approach. The sperm populations of different ejaculate have been measured and quantified. The proof is in the pudding.

Fellahs, you may trust your wife, but your sperm don’t. Measurements show that men, returning home from a long trip, produce a more prodigious amount of sperm—up to 300% more!—for their first copulation with their mate than at any other time. If men see their mate every day, they produce a conservative amount of sperm. The longer the woman is out of sight, the more the male burns extra energy going into sperm production overdrive.

And sperm don’t call in reinforcements just to compete with each other. Sperm use teamwork. Many sperm don’t try to reach the egg, but fan out in kamikaze blocking maneuvers so comrade sperm can reach the coveted egg. It looks a lot like an American football team blocking for their runners. Get out your microscope and watch these mindless little guys run plays.

Teamwork evolves in nature for one reason: to compete against another team. But where is the other team? Who are these sperm blocking and out-flanking? It’s as if the sperm think there is another group of sperm in there.

The scientist’s answer: In all apes, testicle-weight as a ratio to male body-weight correlates with the frequency of female “extra-pair copulations.”

In English: Male chimps have big balls, because female chimps are big sluts. The second a female goes into heat, she sends signals that no human of propriety would consider decent. She inflames her posterior, douses the whole tribe in scent, and tries to copulate with every male she fancies. Female chimps exercise some discrimination, but not a whole heck of a lot compared to a human female. Soon we’ll find out why chimpettes defy the standard model of the coy female.

You’d think this would be paradise for the males. Wrong. Every male chimp is a cuckold. Chimp alpha males are in a tizzy, running around trying to stop secret copulations between females and lower-ranking males, but the female drive for sexual variety outwits the male chimps while they are busy fighting. Alphas can only control one or two of these nymphomaniacs at once, who throw themselves on male penises every time the alpha male’s back is turned. Males can only strategize for a higher percentage of copulations, never for faithfulness. When a chimp female in heat presents her posterior to a male, there could be any number of different guys’ sperms already swimming around in there.

This is why primatologists never watch TV. When females go into estrus, the chimp-offs are pure entertainment. It’s funny, violent, full of chases and trickery, and it’s X-rated—imagine a pornographic Three Stooges– and the researchers get to claim that counting erections is scientific research.

But let’s recover our scientific gravitas. For it’s not until chimp sperm are analyzed that sexual competition takes on an epic scale. So many gallons of semen go into horny female chimps, the sperm have evolved to work as huge armies. They fan out like S.W.A.T. teams, seek and destroy foreign sperm using chemical warfare, swim like speedboats for the egg. Ninety-nine percent of sperm aren’t even sperm. They are anti-sperm, semen of mass destruction. Inside the chimpanzee vaginal tract, it’s a battleground much like an ant battle. The sperm fight it out inside her, leaving only a few sperm standing, from which the egg chooses her favorite.

When it comes to the sexual competition of chimps, some of the competition goes on between the big beasts, but most of the competition goes on between the sperm. Often it’s a war of attrition. The higher your sperm count, the better your reproductive chances. You better believe these chimps are bred for balls.

When the chimp babies are born, nobody knows who is the father of whom, so the male chimps have evolved shared paternity. Female promiscuity pays off in many vaguely interested fathers. Chimpanzee genes have achieved something human ideology never will: socialist paternity: not much incentive, just a shared half-assed sense of duty.

Remember this scientific principle: The sluttier the females, the bigger the balls.

So where do Homo sapiens females fall on the Slut Scale? Let’s check the ball barometer of other apes.

Gorillas have teeny weeny testicles. But they have big shoulders, fangs, and brow ridges. The competition goes on between the big beasts. Sperm can take it easy. There’s no selection pressure for them to compete with other sperm, because nobody has sex with an alpha male’s female without killing the alpha male. Female gorillas are faithful to the promiscuous alpha male. As a result, gorilla sperm can barely figure out which way to swim. Under the microscope, chimp sperm look like Patton’s D-Day, and gorilla sperm look like Hogan’s Heros. The male gorilla only gets to mate a couple times a year at most, and his teensy testicles are all he needs to get the job done.

The orangutan male-to-testicle ratio is slightly bigger than the gorilla’s to account for the rare instance of a two-timing female orangutan.

Look at you, you big ape. Yes, I’m talking to you, Homo sapiens male. What ornaments do you have to distinguish you from a female? Feeble knuckles, slightly more upper body strength, a beard, an ability to read maps, a refusal to use this ability.

Now look at your testicles. Compared to more monogamous apes, yours are slightly … hefty.

Like your brain. Which co-evolved to impress the big brains of females, which co-evolved to impress your big brain. Everything big on you, Homo sapiens male, is big by female choice. Your brain is to wow her with your creations. Your oversized penis—humongous compared to other apes—is to please her sexually. Your balls …

… well, your balls are just big enough to suggest that while you were out hunting on the savanna, back on the Pleistocene homestead, women were having a ball.

Sure, rest assured, they don’t approach the gigantism of a chimp’s. His orgying females have bred his balls to balloon to absurd sizes. Your testicles are one-fourth the body-to-ball ratio of a chimp. But they’re four times the body-to-ball ratio of a gorilla. Look at the faithful female gorillas. Look at the promiscuous female chimps. You fall exactly in between.

To produce enough sperm to fertilize a woman, we only need one half of one ball max. That explains how Benedict Arnold had children. Our balls are an eloquent testament to sneaky hominid women.

Yes, I said sneaky. There is little chance that Pleistocene females attained extra-pair copulations with her mate’s permission. The violent jealousy of Homo sapiens males is well-established. Psychologist David M. Buss’s studies of wife-killing in the USA and among African tribes found that approximately half were caused by sexual jealousy. In the Sudan, Uganda, and India, sexual jealousy is the leading cause of murder. Worldwide, about 20% of all cases of men murdering men result from rivalry over wives and daughters. Scary stats. Yet hominid females who risked grave consequences to steal a tryst on the side passed on enough genes to be represented in our swollen testicles and paranoid sperm.

You just checked them again, didn’t you?

Go on. Feel their weight. Why so much mass to house such microscopic sperm?

I wish there was an alternative theory, but there ain’t. Without cheating females, balls just don’t get big. Nature doesn’t favor organs that require extra energy costs if they don’t confer reproductive advantage.

Conduct the test yourself if you don’t believe me, Homo sapiens male. Next time you ejaculate, grab your microscope. Scientists usually keep one by the bed. (For some reason this doesn’t impress the ladies, despite the romantic light emanating from the bedroom Bunsen burner, but if you are a truly rigorous scientist, a bedroom guest is a rare occurrence for you anyway.) Analyze your fresh sample.

You’ll notice real sperm don’t act like cartoon sperm. Many sperm clasp tails and hold a rearguard bulwark against intruders for several days. To inseminate a female is not just to invest in possible impregnation; it is literally to block her vaginal tract from rival sperm. That’s why men who have not seen their lovers in a few days can triple their sperm count. This does not happen if the man stays home but just doesn’t have sex for a few days. Even if the conscious mind of the homecoming male is assured his mate is faithful, his sperm have never listened to his brain in evolutionary history. Sperm are worried there will be a united front of foreign sperm standing between them and her ovaries, and they arrive in her vagina ready to rumble. Absence makes the heart grow fonder because absence means rivals, and fondness was created by natural selection because fondness re-secured ancestral bonds. Though I wouldn’t recommend saying this in a love letter.

Our conclusion? It looks like Homo sapiens females evolved in an environment mostly monogamous, but occasionally, females copulated with more than one male on the same day.

Makes you insecure? You were engineered to be insecure, Homo Sapiens male. Because you have no positive way of knowing that child is yours. Because jealous men passed on more genes. Because males who would rather kill, die, and mete out severe punishments passed on more genes than men who were fine with their mates accepting sperm donations from other men. We even invented a word for such a fool: cuckold. There is no verbal corollary for a women who is cheated on. No name of shame.

There is a word for promiscuous women, those wily designers of the testicle: slut. There is no corollary for a man who sleeps around. No name of shame. Almost every language in every culture has this double-standard of insults.

Worldwide, the way you insult a male is to tell him his mother is a slut, which is bad. Which means he is a bastard, which is bad. Which means his father was a stud, which is good. In almost all cultures, it’s considered good for males to make women sluts, and make their children bastards, but it’s bad if your mother is a slut or you are a bastard.

These insult double-standards emerged in almost all languages because of statistical differences in how male and female emotions are structured when to protect their genes.

Males of our species should never feel secure in their manhoods until men evolve teensy weensy testicles and disorganized sperm. Our titanic testes are measures of our ancestral cuckoldry.

Next time another male challenges you, “Whatsamatter? Got no balls?” you can answer, “I wish I had less balls.”

Whew! I’m glad that seminal chapter is over with. Now let’s answer The Great Mystery of the Universe.

[Short, R.V. (1979) “Sexual selection and its component parts, somatic and genital selection, as illustrated in man and great apes.” Advances in the Study of Behavior 9: 131-158]

[Short, R.V. (1981) “Testes weight, body weight, and breeding systems in primates.” Nature, 293, 55.]

[Baker, R. and M.A. Bellis. (1995) Human Sperm Competition, Copulation, Masturbation, and Infidelity. Chapman and Hall]

[Buss, D.M. 1994. The Evolution of Desire: Strategies in Human Mating. New York: Basic Books.]

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