CHAPTER SIXTEEN
The Truest Measure of a Man
Small?
Both chimps and bonobos are far more promiscuous than we are. Our testicles reflect this: they are mere peanuts compared to our ape relatives’ coconuts.
FRANS DE WAAL1
Medium?
Convincing vestiges of a sexual selective history in which females mated polyandrously can be found in the human male. Perhaps the clearest vestige is testis size. Men’s testes are substantially larger, relative to body size, than those of gorillas.
MARGO WILSON AND MARTIN DALY2
Large?
Human beings are definitely at the big-ball end of the primate spectrum, more like chimpanzees than like gorillas … suggesting that we have long been accustomed to competing via our sperm as well as our bodies.
DAVID BARASH AND JUDITH LIPTON3
As you can see, there is fundamental disagreement over the male package. What are we talking about here? Peanuts or walnuts? Ping-pong or bowling? Modern men’s testicles are smaller than those of chimps and bonobos, yet they put those of polygynous gorillas and monogamous gibbons to shame, tipping the scales at about half an ounce each (that’s about eighty carats, if you’re a jeweler). Thus both sides of this pivotal debate can claim evidence for their view simply by declaring that human testicles are relatively large or relatively small.
But measuring a testicle is not quite like getting a shoe size. The argument that modern men’s testicles would be as big as the chimps’ if we’d evolved in promiscuous groups is founded on a crucial and erroneous assumption: that human testicles haven’t changed in ten thousand years. When Stephen Jay Gould wrote, “There’s been no biological change in humans in 40,000 or 50,000 years,” he was relying on data that have been supplanted since he died in 2002. This still widely shared assumption grows out of the long-standing belief that evolution operates extremely slowly, requiring thousands of generations to make significant changes.
Sometimes it does. But sometimes it doesn’t. In The 10,000 Year Explosion, Gregory Cochran and Henry Harpending show that the human body is capable of very rapid evolutionary change. “Humans have changed significantly in body and mind over recorded history,” they write, citing resistance to malaria, blue eye color, and lactose tolerance as examples of accelerated evolutionary change since the advent of agriculture.
An example they don’t discuss in their book, but might consider for future editions, is testicular size. Testicles can change size almost in the blink of an eye—blue or otherwise. In some species of lemurs (small, nocturnal primates), testicular volume changes seasonally, swelling up in breeding season and then shrinking back down in the off-season, like a beach ball with a slow leak.4
Testicular tissue in humans, chimps, and bonobos (but, interestingly, not gorillas) is controlled by DNA that responds unusually rapidly to environmental changes. Writing in Nature, geneticists Gerald Wyckoff, Hurng-Yi Wang, and Chung-I Wu report, “Rapid evolution of male reproductive genes is … quite notable in the lineages to human and chimpanzee.” They go on to note that the rapid response of these genes may well be associated with mating systems: “The contrast is intriguing in light of the socio-sexual behaviors of African apes. Whereas modern chimpanzees and bonobos are clearly promiscuous with ample chance of multiple insemination, ovulating female gorillas seem much less likely to be multiply inseminated.”5
Let that soak in for a moment. Humans, chimps, and bonobos—but not gorillas—show “accelerated evolution of genes involved in sperm and seminal fluid production” associated with “multiple insemination.” The genes associated with the development of human, chimp, and bonobo testicles are highly responsive to adaptive pressures, far more so than these same genes in gorillas, where females typically mate with only one male.
Because they are composed entirely of soft tissue, testicles don’t leave a trace in fossils. So, while defenders of the standard narrative assume that human testicular volume has remained constant for millennia, it’s now clear this assumption may be wrong.
Wyckoff, Wang, and Wu confirm a prediction made by biologist Roger Short back in 1979, when he wrote, “Testis size might be expected to respond rapidly to selection pressures. One of the most intense forms of selection will be found in promiscuous mating systems….”6 Geoffrey Miller agrees: “Heritable differences in sperm quality and sperm delivery equipment will be under intense selection.” Finally, evolutionary biologist Lynn Margulis and her co-author Dorion Sagan reason that men’s “souped-up genitals” backed by “a lot of spermatic firepower” would be worthwhile only if there were “some sort of race or contest. Otherwise,” they write, “they seem excessive.”7
Souped-up genitals. Spermatic firepower. Now we’re talking! Indications of spermatic firepower are evident in the differences between a man’s first spurts and his last. A human
ejaculation typically consists of anywhere from three to nine spurts. Researchers who somehow managed to capture “split ejaculates” for analysis found that the first spurts contain chemicals that protect against various kinds of chemical attack. What sort of chemical attack? Aside from leucocytes and antigens present in a woman’s reproductive tract (more on that later), they protect the sperm from the chemicals in the latter spurts of other men’s ejaculate. These final spurts contain a spermicidal substance that slows the advance of any latecomers. In other words, competing sperm from other men seems to be anticipated in the chemistry of men’s semen, both in the early spurts (protective) and in the later spurts (attacking).8
The importance of sperm competition has been debated in scientific conferences and academic journals for the past few decades as if it were a new discovery, but several centuries BCE, Aristotle and his predecessors noted that if a bitch copulated with two dogs during a single fertile period, she could produce a litter of pups fathered by one or both of them. And consider the story of Heracles and Iphicles: the night preceding Amphitryon’s marriage to Alcmene, Zeus disguised himself as Amphitryon and slept with the bride-to-be. The following night, Amphitryon consummated her marriage. Alcmene had twins: Iphicles (fathered by Amphitryon) and Heracles (fathered by Zeus). Clearly, the ancient Greeks had an inkling of sperm competition.
More recently, several researchers have demonstrated that a man’s sperm production increases significantly when he has not seen his partner for a few days, regardless of whether or not he ejaculated during her absence. This finding conforms to the notion that sperm competition has played a role in human evolution and may even reflect an adaptation to monogamy. In this scenario, not knowing what his strumpet of a wife was up to at that damned conference in Orlando leads a man’s body to hyper-produce sperm to increase his chances of fertilizing her ovum when she gets home, even if his worst fears (and possibly, hottest fantasies) are true. Along these same lines, women have also reported that their partners tend to be more vigorous in bed—reporting deeper, more vigorous thrusting—after a separation or if infidelity is suspected.9 (The possibility that the men may actually be turned on by the thought of their mates’ possible transgressions appears not to have made its way into the discussion as yet, but see the discussion of porn below.)
The scandalous implications of sperm competition run smack into the long-held view of sacrosanct female sexuality. It’s a vision Darwin cultivated in public consciousness, featuring coy females who surrender only to a carefully chosen mate who has proven himself worthy—and even then, she’s only doing it for England. “The sexually insatiable woman,” declared a terrified Donald Symons, “is to be found primarily, if not exclusively, in the ideology of feminism, the hopes of boys, and the fears of men.”10 Perhaps, but Marvin Harris offers a different take, writing, “Like all dominant groups, men seek to promote an image of their subordinate’s nature that contributes to the preservation of the status quo. For thousands of years, males have seen women not as women could be, but only as males want them to be.”11
Despite all the controversy, there is no question as to whether sperm competition occurs in human reproduction.12 It does—every time. A single human ejaculate contains anywhere from fifty million to half a billion applicants all trying to elbow their way into the only job available: fertilizer in chief. The relevant question is whether those applicants are competing against only each other, or billions more eager job-seekers sent by other men as well.
It’s hard to conjure a more purely competitive entity than the human spermatozoa. Imagine a teeming school of microscopic salmon whose entire existence consists in straining upstream toward a one-in-several-hundred-million shot at reproduction. Longish odds, you might say. But not all creatures’ sperm face such overwhelmingly slim chances. In some species of insects, for example, fewer than a hundred sperm line up for the race to the ovum. Nor are all sperm tiny in comparison to him that sent them. Some species of fruit fly have sperm that measure almost six centimeters when uncoiled—several times larger than the fly himself. Homo sapiens is far down at the other extreme, depositing hundreds of millions of tiny sperm at the drop of a hat.
Table 4: Sperm Competition Among Great Apes 13
