disparity between males and females—the more polygamous a species, the more males must fight to obtain harems. In the battle for dominance, size is usually the decisive factor, with the larger males monopolizing the females. Their size advantage is then passed along to their offspring so that the males continue to grow larger over time (in biological terms, women’s bodies shouldn’t be considered smaller versions of men’s bodies; rather, women are the norm, and men’s bodies should be considered larger versions of women’s bodies). When a species is monogamous, males and females will be similar in size. For gibbons, a monogamous ape species, the males and females are virtually equal in size. For gorillas, whose successful males typically have harems of three to six females, the males are nearly twice the size of females. You can see this in an even more extreme form with the southern elephant seal. On average, the harem size for a male elephant seal is forty-eight females, so the male is enormous compared to the female—fully three tons compared to seven hundred pounds.
How about human beings? Men are roughly 10 percent taller and 20 percent heavier than women, which indicates mild polygamy. Applying a formula developed by biologists, we can estimate that male body size indicates harems of two to three women. But there is some good news. We appear to be evolving in a more monogamous direction. A few hundred thousand years ago, men used to be one and half times the size of females, so our current 20 percent difference represents a distinct decrease. If we give it another couple of hundred thousand years, we may find that men and women match each other exactly and live in perfect monogamous bliss. Of course, this measurement may no longer be as relevant as it once was. Men don’t go around these days competing for women using feats of strength. The competition tends to be mental, rather than physical, which may also account for the shrinking size differential.
. . . AND SLIGHTLY PROMISCUOUS WOMAN
Before women start bemoaning men’s lackluster commitment to monogamy, they should realize that there are also indicators that women are quite likely to stray from monogamy as well. In this instance, the key measurement is testicle size because testicle size and sperm production vary directly in relation to female promiscuity. The reason for this is quite simple—sperm competition. If a female has sex with multiple partners during ovulation, the more sperm a male can ejaculate increases his chances of being the father. Chimpanzees live in large social groups where there is a high degree of promiscuity among the troop—so much so that male chimps can rarely, if ever, be sure of the paternity of a baby chimp. Not surprisingly, chimps have enormous testicles. Gorillas, on the other hand, live in much different circumstances. A male is the only one to mate with his harem as long as he remains unchallenged. Consequently, a gorilla’s testicles are quite small. The comparison between the two species is nothing short of astonishing. Despite being only a quarter the size of gorillas, chimpanzees have testicles that are roughly four times larger. Adjusted for body weight, the disparity is even greater. Biologists have found a similar link between testicle size and mating systems of birds—the largest testicles were found in species where several males fertilize one female.
So just where do human beings fall on this scale? Somewhere in the middle, although closer to the big ball end of the spectrum. Men’s testes weigh in at an average of two and a half ounces. Our testicles are roughly the size of a gorilla’s, even though a gorilla weighs roughly 450 pounds, and the average man weighs only 175 pounds. A chimpanzee’s testicles are almost twice as large as our own, even though a male chimpanzee weighs on average one hundred pounds. To give a rough approximation based on body size, male gorillas’ testicles
How about human beings? Men are roughly 10 percent taller and 20 percent heavier than women, which indicates mild polygamy. Applying a formula developed by biologists, we can estimate that male body size indicates harems of two to three women. But there is some good news. We appear to be evolving in a more monogamous direction. A few hundred thousand years ago, men used to be one and half times the size of females, so our current 20 percent difference represents a distinct decrease. If we give it another couple of hundred thousand years, we may find that men and women match each other exactly and live in perfect monogamous bliss. Of course, this measurement may no longer be as relevant as it once was. Men don’t go around these days competing for women using feats of strength. The competition tends to be mental, rather than physical, which may also account for the shrinking size differential.
. . . AND SLIGHTLY PROMISCUOUS WOMAN
Before women start bemoaning men’s lackluster commitment to monogamy, they should realize that there are also indicators that women are quite likely to stray from monogamy as well. In this instance, the key measurement is testicle size because testicle size and sperm production vary directly in relation to female promiscuity. The reason for this is quite simple—sperm competition. If a female has sex with multiple partners during ovulation, the more sperm a male can ejaculate increases his chances of being the father. Chimpanzees live in large social groups where there is a high degree of promiscuity among the troop—so much so that male chimps can rarely, if ever, be sure of the paternity of a baby chimp. Not surprisingly, chimps have enormous testicles. Gorillas, on the other hand, live in much different circumstances. A male is the only one to mate with his harem as long as he remains unchallenged. Consequently, a gorilla’s testicles are quite small. The comparison between the two species is nothing short of astonishing. Despite being only a quarter the size of gorillas, chimpanzees have testicles that are roughly four times larger. Adjusted for body weight, the disparity is even greater. Biologists have found a similar link between testicle size and mating systems of birds—the largest testicles were found in species where several males fertilize one female.
So just where do human beings fall on this scale? Somewhere in the middle, although closer to the big ball end of the spectrum. Men’s testes weigh in at an average of two and a half ounces. Our testicles are roughly the size of a gorilla’s, even though a gorilla weighs roughly 450 pounds, and the average man weighs only 175 pounds. A chimpanzee’s testicles are almost twice as large as our own, even though a male chimpanzee weighs on average one hundred pounds. To give a rough approximation based on body size, male gorillas’ testicles
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