Sex, Time, and Power

by Leonard Shlain

  Animals, in contrast, are composed of tissues that abound with iron in an easily absorbed ferrous and ferric form, known as heme iron. Bone marrow, liver, and muscle tissue (meat) brim with heme iron. Aiding absorption is the quirk of our digestive tract’s metabolism that allows the cells lining the stomach to transfer heme iron more easily into the interior of blood vessels if it is in the presence of other animal proteins. Ancestral humans must have intuited that eating meat was the fastest, easiest way to absorb iron and maintain vigor. Though they did not understand biochemistry, they surely would have developed a native intelligence on matters concerning health.

  Another consequence of the change in the human diet from vegetarian to carnivory: The more meat we ate, the shorter our gut became. The shorter our gut became, the more oxygen was available to nourish a brain that grew in size.* Most animals allocate the greatest portion of their available oxygen to their alimentary tract. Digesting plant food is hard work and requires a high-energy source. Upon switching over to a diet high in animal products, the gut no longer needs so much oxygen, and the excess that is freed can be diverted to the brain. A few nonhuman primates—for example, chimps, capuchin monkeys, and baboons—eat meat but not as a major food. Those few that do are the most intelligent nonhuman primates. In general, carnivores are smarter than herbivores; foxes are slyer than donkeys.

  If humans were becoming increasingly dependent on oxygen-consuming brains, one might predict that obstacles to the digestion and the absorption of iron would diminish. Instead, they increased. Why did a human lose the genetic instructions that create the enzymes to take in plant iron easily? If prodigious brains depend on the timely delivery of great gasbags of oxygen, why would impediments to the absorption of the key to its transport, iron, coevolve with our increasing dependency on iron? And why would there be a marked gender disparity in the frequency of iron deficiencies that seriously affect health?

  Along with pigs and hippopotami, humans are hearty omnivores. They can derive sustenance from a wide variety of both plant and animal foods. But they must partake of each food group. A vegetarian easily avoids dietary deficiencies by eating dairy products. A vegan is distinguished from a vegetarian by abstaining from eating any animal-related food, including eggs, milk, and cheese. A man adopting a vegan diet is at low risk for developing a serious anemia. A woman in her reproductive years without access to modern nutritional knowledge who makes the same choice cannot avoid anemia. She must ingest some supplementary form of iron or risk injuring her health and the health of her unborn baby. Natural Selection seems to have rigged the human’s digestive tract so that humans, especially females, would have to acquire iron from the flesh of another animal. Before discussing how women solved this dilemma, let us examine what happens to the iron that does make it across the intestinal barrier into the bloodstream.

  An atom of iron successfully transiting the human stomach and intestinal lining is rapidly chelated by apoferritin, a specialized deliveryman protein bobbing along in the bloodstream waiting for a shipment.* Once it has taken iron atoms on board, ferritin, as it is now called, transports its charges and deposits them primarily into the bone marrow. When not engaged in making its daily rounds in a red cell’s hemoglobin, excess iron is also stored in the liver.

  When red-cell levels fall—for example, as a result of bleeding from any cause—sensors within the bone marrow and the interior of the kidneys note the deficit and issue orders to ramp up production of both the hemoglobin protein and new red cells. Once the bone marrow ascertains that red cells have reached maturity, it releases these compact discs into the bloodstream. There each cell begins its nonstop work shift, shuttling back and forth between lung and distant cell, carrying its indispensable hod of oxygen. A red cell has a life span of approximately 120 days. As it nears decrepitude, specially designed sentinels in both the spleen and the liver identify and then yank these seniors off the line. They crack open the red cell’s membrane, break down its hemoglobin into simpler components that can be used for other purposes, and extract the senescent red cell’s semiprecious iron ore.

  Recycled back to the bone marrow, a single atom of iron will later be incorporated into a new red cell, and another 120-day cycle will begin. Iron atoms never tire or wear out; they are indestructible—the perfect reusable part. Nearly all vertebrates, up the evolutionary ladder from fish, depend on hemoglobin and its reliable atom of iron to transport oxygen.

  When an animal dies, its body decomposes and its iron dissipates and eventually settles into the soil. There the worms churn it. A seed, blown by the wind, lands gently nearby. Soon roots of what will become a new plant are tentatively exploring the subterranean neighborhood. A root’s tentacle sucks the iron in the soil into its substance, and the iron atom finds itself an integral part of the new plant’s infrastructure. And then, one fine day in spring, a shy green tendril nudges aside the loam to find its place in the sun. As the plant grows, the iron that began in the soil moves into the upper stories of the plant’s leaves. Eventually, an herbivore may come along and eat the plant. Perhaps a carnivore will then eat the animal that ate the plant, and the iron will find itself in yet another silo. This cycle will go on and on as long as the sun continues to shine and the earth abides.

  When biochemistry became advanced enough to measure the concentration of the various vital elements circulating in a human bloodstream, researchers discovered that women had significantly lower levels of circulating red blood cells, hemoglobin, and iron stores than did men. Unable to explain this discrepancy completely, the clinicians who set the standards for what is normal decided, somewhat tentatively, that it was normal for a woman’s red-cell and hemoglobin parameters to be 15 percent below those of her male counterpart.

  Implicit in their determination is that women should be able to get by normally on less hemoglobin than men do, or that women’s metabolism is more efficient.* No evidence exists that cellular oxygen transfer in a woman differs from that of a man. Basic metabolic enzymatic processes, as a rule, make no distinctions between sexes. Current conditions among contemporary women living in technologically advanced cultures that routinely fortify food with iron should not obscure the fact that ancestral females living in the Pleistocene would have constantly teetered on the edge of developing a chronic iron-deficiency anemia. A woman’s best defense against this pathological condition’s subtle and deleterious effects on both her health and the intelligence of her unborn children would have been to consume foods rich in iron in its readily absorbable heme form. (Or, alternatively, to live in an environment that contained rich sources of plant iron in easily gathered, abundant quantities.) Men do not need supplementary iron, because losing it is not part of their physiological makeup. Women, on the other hand, have to have it.

  Gyna sapiens’ reproductive life cycle was a dramatic departure from all that had gone before.

  Chapter 5

  Gyna Sapiens/Gyna All-the-Others

  The female sexual response was evolved and perfected many millions of years ago…certainly in creatures far simpler and more primitive than ourselves. The reason they make so little fuss about it is precisely because it had been perfected; it was as simple and effortless as eating, and the reward in terms of pleasure was as automatic. So the question to which we ought to be addressing ourselves is not, How and why did the human species evolve this frightful complicated and mysterious female mechanism? It is rather, How on earth did the human species come to lose, mislay, and/or generally louse up such a simple straightforward process?

  —Elaine Morgan1

  The psychosexual pattern in man looks very much like the end product of a biological emergency.

  —Alex Comfort2

  The two factors that advance a sexually reproducing organism to the next evolutionary round are its ability to survive to reproductive age and its success in mating with the opposite sex. Jackpot bells ring throughout the evolutionary casino when half the organism’s DNA drops down into the next generation in
the form of a healthy offspring. The new organism, having received genes from both a fit mother and a fit father, then begins the arduous competition of surviving long enough to reproduce. And so it has gone—for millions of years. Gyna sapiens experienced the most dramatic changes in the genes responsible for her reproductive cycle. Homo sapiens underwent the greatest genetic revolution in the genes controlling his survival strategies.

  When attempting to understand why a particular human trait evolved, an evolutionary biologist seeks to discover the benefit the trait confers upon individuals within the species in increasing the odds of either survival or reproductive success. When an inherited trait seems at first glance to be deleterious, then the researcher must look beyond short-term disadvantages and search for a less obvious long-term benefit.* Confusing the issue is the possibility that the trait under scrutiny might have nothing to do with enhancing survival or reproduction, and instead might simply represent a spandrel of no evolutionary consequence. Spandrels, remember, are evolved traits having no particular impact, either positive or negative, on survival or reproduction.

  Evolution’s most useful metaphor is a branching bush. Our two closest relatives, Pan troglodytes (common chimpanzees) and Pan paniscus (pygmy chimpanzees or bonobos), are linked to us by a yet-to-be-identified Last Common Ancestor, from which we three apes evolved around five or six million years ago. The hominid line branched into us, and the other fork split again into two end twigs, on the tips of which at present sit our two slightly different chimpanzee cousins. Jared Diamond titled one of his books The Third Chimpanzee, reminding us that we humans were the third member of this small family. Yet, despite our close chimp kinship, a human female’s sexuality differs significantly from that of her close cousins and varies even further from other nonhuman females.†

  The disparity between Gyna sapiens’ reproductive life history and the females of her nearest relatives is so great that a veritable army of Ph.D.s seek to explain the reasons for her considerable distance from what constitutes the crest of the reproductive bell-shaped curve for other, nonhuman females. Yet a consensus among interested scientists has thus far failed to gel. Part of the reason Gyna sapiens’ evolutionary picture remains so opaque is that each of the revolutions in her reproductive life story, examined individually, seems to have either mightily or slightly disadvantaged her in the competition for resources, survival, and reproductive fitness. Let us examine each of her unusual adaptations with an eye to evaluating its potential benefit against its possible harm to her reproductive fitness.

  One unusual trait in human females that has baffled scientists for years is cryptic ovulation. A male of the human species does not receive any reliable clues as to the moment when a female ovulates. So secret is her ovulation that she, too, is generally unaware of the moment of the Great Launch. Because cryptic ovulation is intimately associated with both Gyna sapiens’ loss of estrus and her potential for continual sexual receptivity, I will discuss all three of these interrelated features together.

  In the majority of primate species, a female in estrus displays spectacular physical manifestations as ovulation approaches. Her vulvar sexual skin (best seen from behind by the male) blushes a flaming red and swells with edema fluid, sometimes impressively. The sight of a female in such a state stimulates the male tumescently. Excitatory pheromones waft from her vulva, further agitating the troop’s males.

  In case the male does not express the appropriate interest in this sight-and-smell show, the female primate will actively solicit copulation by presenting him with an enticing, up-close rear view. In a few species—for example, the gray langur—the female will position herself directly in front of a male and perform a shuddering movement of her head and/or stroke the male with her hand in an imploring manner. Still others emit a distinctive call. Singularly or in some combination, the females of 269 primate species use call, smell, sight, touch, and/or gesture to announce their sexual receptivity. One does not. Her secretive ovulation separates Gyna sapiens from other mammals as well. Reproductive evolutionist Margie Profet declared, “The only mammal whose ovulation is known to be truly concealed is Homo sapiens.”4

  Gyna sapiens does not emit a consciously detectable odor or distinctive sound when she ovulates. Her facial expression does not change, nor does her body stance. She does not gesticulate in a come-hither fashion. The patch of dense pubic hair unique to humans obscures any hints of a color change in her vulvar skin.* Outer clothing worn by most women in both indigenous and advanced cultures serves to increase a male’s uncertainty.†

  A few women, particularly young women, do receive an unwelcome alert that announces the precise moment of their ovulation. Mittelschmerz, a German term meaning “middle-of-the-month pain,” is a well-recognized medical syndrome. Occasionally, a small amount of internal bleeding accompanies the bursting of the ovarian bubble follicle containing her ovum. Blood irritates the peritoneal lining, causing localized abdominal pain. Many a young woman has been misdiagnosed with appendicitis because of her physician’s confusion in trying to tell these two nearly identical clinical presentations apart. As a woman ages and her ovary’s husk becomes more pliable, Mittelschmerz markedly diminishes in both severity and recurrence.

  Some women are exceptionally attuned to their bodies and can intuitively monitor changes in their circulating hormonal levels and use these fluctuations to inform them of the key moment when their eggs are ripe. For the majority of women, however, ovulation is truly cryptic. Family planning requires more reliable information on this issue, and lack of certainty prompts many women to purchase thermometers and cervical-mucus density kits to pinpoint accurately their internal cycle’s apogee.

  In every other species, it is extremely advantageous to survival and reproduction to have females signal males that the time is right. What possible benefit would there have been to losing so crucial a primal instinct? This stark chasm dividing a woman from the majority of other primate females—as well as virtually every other species of insect, arthropod, fish, reptile, bird, and mammal—has been the source of endless speculation. The most commonly accepted theory is that a woman’s cryptic ovulation, year-round sexual receptivity, and loss of estrus solidifies the bond between her and her mate, convincing him to stay and help her raise their children. Cryptic ovulation, according to this line of reasoning, increases the need for abundant sexual intercourse, and this in turn heightens intimacy.

  Jared Diamond calls this the “daddy-at-home” theory. Citing the work of Richard Alexander and Katherine Noonan, Diamond argues that a woman had to conceal her ovulation; otherwise her husband would only stay with her when she was exhibiting signs that she was fertile.5 The rest of the time, he would be out trying to find other women, who were exhibiting signs that they were sexually ready. His absence would be detrimental to his children, and by concealing her ovulation, a woman convinced a man to stay by her side and make love to her throughout the month, so that he could be sure he was fathering the children she bore.

  Several flaws and inconsistencies, however, weaken the argument that promotes sex as the glue holding human relationships together. If sex served the purpose of ensuring the durability of the human parenting commitment, then parents should become more ardent in their lovemaking following the birth of a baby. Instead, the opposite occurs. Both parents routinely report a sharp fall in their respective libidos following the blessed event.6

  While a mother focuses on tending to her babies, other females, who are also enjoying year-round sexual receptivity, can surreptitiously compete for the affections of the father. Given his hyperkinetic sex drive, it could be reasonably argued that cryptic ovulation, loss of estrus, and year-round sexual receptivity work to a new mother’s disadvantage and are just as likely to precipitate marital dissolution as promote marital bliss. The peccadilloes reported in the daily newspapers provide ample corroborating evidence for this observation.

  Year-round female receptivity is not necessary to strengthen the sexual rela
tionship among any other monogamous species. Wolves, geese, coyotes, gibbons, albatrosses, and prairie voles mate for life without the female’s having to lose her “season” to entice the male not to stray.

  Many other inventive theories attempt to explain why ovulatory signals disappeared in the human line, but none of them, in my opinion, propose an advantage so sterling that it offsets the abandonment of the premier gene-replicating method used by millions of species over millions of years—females signaling males their sexual readiness at the same moment they are ovulating. The few species of primates that do not ostensibly signal ovulation are distant from the human line on the evolutionary primate-branching bush. A few other species’ females also do not appear to advertise their ovulation—for example, some birds, such as mallards—but the problem of knowing for sure is exacerbated by the fact that human observers can’t ask the males of these species whether or not they are aware of the females’ ovulation.

  Among the more ingenious explanations for why sexual signaling disappeared in humans is the one proposed by anthropologist Nancy Burley. Women lost the ability to monitor their ovulatory moment, according to Burley, because those who grasped the connection between sex and pregnancy realized that pain, possible death, and taxing demands were also part of the deal. A woman so enlightened, Burley theorizes, might prudently decide to abstain from sex.7 Celibates do not leave offspring. Selection pressure would, therefore, favor those women who were unaware of their ovulation.