Primatologist Sarah Blaffer Hrdy proposes that infantile murder coaxed human cryptic ovulation into being in a theory known as the “many fathers.” Having carefully documented the horrifying fact that male primates sometimes killed infants, Hrdy posits that the loss of external signs of ovulation ultimately protected newborns by keeping all parties guessing concerning the issue of paternity, especially males. Unsure whether an infant was due to his copulatory efforts, a male would be less inclined to kill it. Hrdy worked primarily with hanuman langurs, but other studies, including Jane Goodall’s chimpanzees in the wild and Alison Jolly’s ring-tailed lemurs, have confirmed that males commit infanticide in these species. To date, thirty-five species of primates have been identified in which strange males kill infants.8
Social scientists Margo Wilson and Martin Daly found suggestive evidence that this abhorrent practice exists among humans. Surveying crime statistics, they noted that when an adult male murders a child he is sixty-five times more likely to be a stepfather or live-in boyfriend than the child’s biological father.9
Though I have great respect and admiration for Hrdy’s work, I wonder whether her theory is the whole story. If infanticide was so great a threat to the continuation of affected primate species, why did only the human line adopt the evolutionary strategy of cryptic ovulation to solve the problem? Chimpanzees, for whom infanticide is a serious problem, have not evolved anything resembling cryptic ovulation. Bonobo males have never been observed to engage in killing infants, yet bonobo female primates come closest to mimicking the human female’s reproductive model of loss of estrus and increased sexual receptivity.
The observation that strange males do the killing is in keeping with evolutionary theory. Alpha maledom often does not last very long. A strange male who achieves dominance must make hay while the sun shines. By killing the sucklings of his new group, he can precipitate estrus among the distressed mothers and thus increase his chances of spreading his genes. Among human populations, it has been a common strategy of conquering armies, after beheading the losing side’s warriors, to turn their attention to killing the infants who the conquerors know were fathered by those warriors. This slaughter of the innocents has been amply recorded at different times in disparate locales throughout history. Cryptic ovulation has rarely protected infants of the conquered women from being killed by strangers.
If keeping the male uncertain concerning paternity increases the life span of children, what would be the advantage to the female of remaining in the dark on such a vital issue as her own ovulation? Another question: The male primates that engage in the practice of infanticide do not seem to care one fig about the offspring they do sire. Since the majority of infanticide is carried out by recently arrived males that are strangers to the group, it would be safe to assume that these animals are equipped with an instinct to kill the infant of any strange female. Hrdy’s theory rests on the assumption that a male primate is capable of making the causal connection between sex and birth, either instinctually or consciously. There is minimal scientific evidence to indicate that this quantum leap in logic has occurred in the mind of another species besides a human.* Another problem: Since knowing when a female ovulates is critical to a male’s fitness, why did not the human male develop a compensatory counteradaptation to detect the female’s ovaries’ subterfuge?
Many other theories abound. Donald Symons suggests women use their year-round sexual receptivity to seduce philanderers in exchange for gifts.10 L. Benshoof and Randy Thornhill propose that cryptic ovulation allows a woman to mate by stealth with a superior man without alerting her husband.11
Though the theories outlined above may have been contributing factors in reprogramming Gyna sapiens’ reproductive cycle, they do not seem to offer sturdy enough reasons to explain the origin of such drastic changes in her life strategy. The rarity of concealed ovulation among the other three million sexually reproducing species suggests that cryptic ovulation is not a mainline solution to any of the problems posed by the various theories.
The primary consequence of cryptic ovulation—the need for increased sexual contact to coincide with ovulation’s propitious moment—would appear to be highly disadvantageous, evolutionarily speaking. In the cold calculus of energy conservation, copulation is both dangerous and a very expensive metabolic activity. An ancestral couple in flagrante delicto would have been very vulnerable to a predator. Sex consumes time, calories, resources, and mental effort that might better be used for survival. With a few notable exceptions, other creatures expend minimal time and energy copulating. The mating act of most birds and mammals can be measured in seconds.* The human investment, in terms of time spent thinking about sex, planning, wooing, and actually engaging in the act, exceeds that of any other creature. After their strenuous coitus, humans generally require a longer recovery interval than any other animal.
Additionally, without a visible or olfactory lodestar, men and women have found it necessary to engage in frequent, capricious copulations throughout the year to increase the likelihood of pregnancy. The uncertainty of conception, both for those who yearn for it and those who don’t, has been among men’s and women’s most consistent causes of stress, anguish, and anxiety down through the generations. Evolutionary processes do not care whether an organism is happy or not. Nevertheless, stress tends to diminish an organism’s fitness.
Nonestral females of other species, with rare exception, do not appear to begrudge the attentions estral females receive from excited males. When Gyna sapiens lost estrus and gained the ability to engage in sex anytime throughout the year (if she so desired), the nettlesome problem of sexual jealousy among women reared its ugly head. The green-eyed monster consumes a staggering waste of spirit and is virtually unknown among other species.
Cryptic ovulation and year-round sexual receptivity also greatly increased the amount and degree of jealousy among many men. Societies have had to construct draconian legal, social, religious, and cultural barriers to regulate members’ sexual competition and minimize the outbreak of violence. Duels, dogmas, eunuchs, taboos, so-called honor killings, chastity belts, and female genital mutilation are just a few of the rituals and devices that attest to the difficulty men have had in dealing with women’s robust sexual capability.
Desmond Morris in his book The Naked Ape makes the argument that humans are the first species to elevate sex to the status of a recreational activity.* Morris speculates, “The vast bulk of copulation in our species is obviously concerned, not with producing offspring, but with cementing the pair bond by providing mutual rewards for the sexual partners.”12
According to this argument, endorsed by many others besides Morris, we are Homo ludens (the Playful Ape) and we have liberated sex from the depths of the Minotaurean labyrinth† in the brain’s primitive limbic system of instinctual drives. By elevating sex to the brain’s higher, neocortical planes, according to these authors, we have created a new kind of sex. Proponents argue that the pleasure we so derive and the love that enhances the deep human commitments more than offsets any of the disadvantages of drastic changes in sexual programming.
I, for one, am not so sure. The many downsides of cryptic ovulation, loss of estrus, and a woman’s continual sexual receptivity do not seem to balance the purported advantages. The reason that this unusual constellation of female reproductive changes constituted an incontestable plus for humans lies in an area far removed from sex itself. Before I make that case, we must continue to enumerate several other features of the Gyna sapiens’ life history that separate her from her nonhuman sisters. Only after all the pieces of the puzzle have been identified can we begin to see how they all fit together.
Another feature indicative of Gyna sapiens’ radical reproductive makeover is the mysterious way a close-knit group of women synchronize their menses. Nobel Prize laureate Barbara McClintock demonstrated that unconsciously detectable pheromones emitted by the alpha female in the group mediated this mysterious process.13 Women who menstruat
e together must by necessity also ovulate together. Contemporary societies typically comprise large numbers of unrelated strangers constantly in flux who rarely congregate in one place for any extended period of time. In contrast, ancestral women often lived most of their lives in close association with female members of their tribal group or clan whom they knew quite well. Our modern disruption in the living arrangements under which women lived for over 99 percent of our species’ history has profoundly attenuated and obscured what was formerly a transformative evolutionary reproductive trait.
Among most other creatures, circadian rhythms synchronize ovulation to create mass breeding seasons, timed to coincide with optimal environmental conditions. Primates are a notable exception to this general rule. Both bonobos and common chimps cycle in and cycle out at various times of the month, and their pattern is the norm among other apes and monkeys. The ring-tailed lemurs of Madagascar, a primate species many limbs and branches away on the primate order’s family tree from humans, are one of a handful of Gyna sapiens’ primate sisters to coordinate their reproductive phases instinctually. Typically once a year on the night of a full moon, ring-tailed lemur females ascend in lockstep to the pinnacle of estrus. All the males, as one would expect, go wild. What follows is a lunar mass sexual orgy.*
Biologists do not know at what point in our evolution Gyna sapiens evolved the unique feature of menstrual harmony.† As with any major novel adaptation, there would most likely have been multiple reasons why Gyna sapiens synchronized menses, but one subtle effect was to accelerate her liberation from the grip of male tyranny.
The majority of species manifest a disparity between the size of the male and the female. Biologists call this trait “sexual dimorphism.” Among invertebrates (insects, worms, etc.), females tend to be larger than males; among vertebrates, especially birds and mammals, males tend to be bigger. Ethologists ‡ use a species’ dimorphic ratio to predict its mating pattern. Whenever the male is disproportionately larger than the female, he uses his superior strength to fight other males for possession of the females, whom he overbearingly protects but keeps in sexual thrall. When males are nearly equal in size and weight to females, then cooperation and monogamy tend to be the norm.
Silverback gorillas and hamadryas baboons are two extreme examples of primate sexual dimorphism. The alpha males are more than twice as large as the females, and they thoroughly dominate the members of their respective troops and herds. The alpha male, along with his close allies, brusquely fends off lower-ranking males who attempt to mate with “his” females. In some species of monkeys, powerless males never gain the opportunity to have sex at all, and the despotic alpha male’s hard-won monopoly deprives females of choice. Females of sexually dimorphic primate societies do not synchronize their estrus or menses but, rather, phase in and out of sexual receptivity in a random fashion, a perk not lost on the alpha male, who jumps on every chance to mount one estral female after another.
A group of females cycling in unison, however, dramatically alters the equation. Menstruating in synchrony means that all the females also coordinate their estrus and ovulate nearly simultaneously. Imagine an alpha gorilla’s or an alpha baboon’s astonished confusion if all the females in his group simultaneously approached him, each presenting her hind, demanding relief. His initial delight over this novel situation would soon turn to consternation. A solitary male, despite his well-advertised sexual prowess, would discover that it was exceedingly problematic to satiate insatiable females if they all demanded sex from him at the same time. Should he try, he would most likely find himself exhausted and depleted, lying flat on his back, nursing a sore penis. In these circumstances, he would presumably welcome the assistance of lower-ranking males.16
Through a clever adaptation, females would now have a much greater selection of males, other males would finally get a chance to discover what all the hoopla was about, and, in general, the entire troop would be happier and more content. By menstruating in sororal harmony, ancestral Gyna sapiens broke the back of the system that rewarded the strongest, fiercest, males with a sexual monopoly. In short, synchronized menses enhances female equality.*
Underscoring this last statement: Female ring-tailed lemurs, one of the few nonhuman primates to habitually synchronize their menses, belong to the only primate species, other than humans, in which a female can completely dominate a male. Allison Jolly observed on many occasions that a diminutive female approached a large male busily eating, snatched the food away from him, cuffed him on the ear for good measure, and then sauntered off to enjoy her ill-gotten gain in privacy. No other female of any other primate species (except Gyna sapiens) would routinely dare so brazen an act.18
Anthropologist Chris Knight has proposed that women synchronized their menses in order to organize a sex strike and force men to go hunting to bring them meat. He wrote in his comprehensive 1991 book, Blood Relations:
For babies to be conceived, the sexes had to come together. For efficient hunting to take place, they had to separate. If both hunting and conception were to occur, the sexes had to alternate between conjunction and disjunction. Periods of sex strike and marital togetherness had to alternate. I assumed that this alternation must have been socially synchronized, rather than a matter for individuals to decide autonomously within couples.19
Backing up his arguments with a wealth of ethnographic data, Knight makes the case that menstrual rituals were among the first and most important rites performed by early humans. The liberal use of red ochre for body adornment in these rituals became the basis for many human cultural innovations that followed.
Menstrual coordination played a key role in the evolution of our species. When this was joined with cryptic ovulation, loss of estrus, and potential year-round sexual receptivity, conditions began to coalesce that fueled the explosive rocketing of the human species to a position far ahead of all the others in the competition for resources. Several additional, extremely unusual components that occurred in Gyna sapiens’ life cycle require investigation before the overall pattern emerges. Like an emulsified photo from a Polaroid camera forming a picture before our eyes, additional enhanced details are necessary before the frame comes into focus. When all the components of her reproductive life history are recognizable against the background of the snapshot, I will propose in chapter 13 a theory to explain how the picture’s many diverse parts interrelate.
Because of the superb olfactory sense of most predators, menses would have imperiled a ground-dwelling human female.
Chapter 6
Periods/Perils
Greater than his fear of death, dishonor, or dismemberment has been primitive man’s respect of menstrual blood. The measures he has taken to avoid this mysterious substance have affected his mealtimes, his bedtimes, and his hunting season; and primitive woman, unable to separate herself from her blood, knew that upon her tabooed state depended the safety of the entire society.
—Janice Delaney, Mary Jane
Lupton, and Emily Toth1
None of the known features of female mammalian reproductive physiology require menstruation as an ineluctable by-product. If menstruation were both costly and functionless, natural selection would have eliminated it long ago.
—Margie Profet2
Around the time that Gyna sapiens was abandoning the outward signs of ovulation, her menses, initially of minimal consequence, evolved into a copious and potentially dangerous blood loss. On examination, there appear to be many drawbacks to this feature without a single obvious compensatory advantage. Physiologists would protest, pointing out that human menses is the inevitable end result of the extraordinary preparations the uterine lining must undergo to implant a fertilized ovum successfully. But 3,999 out of 4,000 other mammalian species’ females pump out litters with as many as ten kits, cubs, pups, and piglets without having to discard significant amounts of blood and protein-rich tissue monthly. Some mammals, such as dogs, bleed during their period of heat. But nature has equipped them with t
he instinct and the anatomical flexibility to lick themselves, thus allowing them to recycle their iron and prevent deficits.
Menstrual discharge emanates a distinctive odor. Most predators rely heavily on their olfactory sense. The smell of menstrual blood does not pose a threat to the other thirty species of menstruating primates. Discharged by a high-flying monkey or an acrobatic langur, the minimal dribs and drabs fall through the tree branches below, spattering in dense foliage. Most droplets do not even reach the ground. Should a leopard, snuffling along the forest floor, happen to pick up the scent of a menstruating monkey, the weakness and inconsistency of the signal would be of little assistance to it in locating dinner. Even if the leopard could follow the scent, this would not necessarily result in a kill, because primates have few natural enemies, and even fewer that can catch them in treetops.
Given the conditions under which our ancestral hominids lived in the Pleistocene, however, menstrual blood’s distinctive odor would pose a much more serious threat for a bipedal hominid female. Judy Grahn in her 1993 book, Blood, Bread, and Roses, recounts the following incident.
Once when I was living in an all-female collective some visiting dogs “went wild” for a few hours one afternoon while we were out. They broke into laundry baskets and ate the crotches out of a half a dozen pairs of Levis and dress pants!…That was the day I began to imagine the hazards of being a menstruating woman in the vicinity of blood smelling predators, in those long eras before we learned to use fire, weapons, or houses. How cautious one would need to be. How silent. What to do? Hide, bury yourself in the sand, climb a tall tree?3
Sex, Time, and Power Page 8