Sex, Time, and Power Page 3

  Iron, Sex, and Women

  Part I

  The emergence approximately 150,000 years ago of Homo sapiens, an animal that opened a chasm between it and all other species, was as improbable an event as coming upon a nude Caucasian woman reclining on an Empire couch in the middle of the jungle.

  Chapter 1

  Unknown Mother/African Eve

  Sex endows the individual with a dumb and powerful instinct, which carries his body and soul toward another; makes it one of the dearest employments of his life to select and pursue a companion, and joins to possession the keenest pleasure, to rivalry the fiercest rage, and to solitude an eternal melancholy. What more could be needed to suffuse the world with the deepest meaning and beauty?

  —George Santayana1

  The reconstruction of evolutionary history is better regarded as a game than as a science, evolutionary hypotheses should be stated with varying degrees of confidence always keeping in mind that certainty cannot be achieved.

  —Sherwood Washburn2

  She died an agonizingly slow and painful death. She was not accorded funerary rites, nor was her corpse laid to rest in a grave. Her remains constitute but a sliver of debris—a disconnected tooth here, a chip of a fossilized bone there, fragments lost in the strata of bygone ages. At the time of her death, she represented the latest in a line of primates called “hominids” that had begun their evolutionary trial run several million years earlier. If paleontologists ever find her final resting place, we should erect a memorial on the spot in recognition that she did not die in vain. An appropriate name for her marker would be “The Tomb of the Unknown Mother.” Her passing heralded the birth throes of a new species.

  Imagine that a group of intergalactic anthropologists had been observing these primates from the beginning. When Unknown Mother died, the visitors would have exchanged knowing looks, because they could plainly see that her fate was foredoomed. The hominid line from which she arose had split away from other primates by developing two adaptations destined to collide. Hominids were the only primates to depend on a new means of moving about that required only two limbs instead of four. An upright stance allowed them to clamber down from the trees and seek a living first on the forest floor and later on the open savanna. Because their erect posture greatly increased the possibility that the first creature to stride would end up as “cat food,” they needed a crucial second adaptation. Since they could not outrun or outfight predators, they required an enlarged brain capable of outwitting those creatures intent on devouring them.

  During the last two and half million years, the hominid brain had tripled in size but the opening in the pelvic girdle through which this rapidly enlarging brain had to pass at birth did not keep pace. These two adaptations—two-leggedness and watermelon-sized heads—were clearly incompatible.

  The new engineering imperatives of standing upright had sculpted the hominid’s pelvic ring of bone into a new shape, flattening it from front to back. The bipedal pelvis, anatomically dissimilar to its counterpart in four-legged animals, also acquired a novel architectural function. It had to serve as a basin to contain the mass of intestines pressing down from above and prevent them from falling down and out through the rectum. Consequently, the bony hole in the pelvis had to remain relatively small. Only the wide, comparatively horizontal flanges of the human iliac pelvic bones, the narrowness of the pelvic inlet, and the thin sheet of muscles suspending the anus prevented this unusual primate from having the discomfiting experience of being turned inside out while out for a stroll after a particularly heavy lunch—a gravitational hazard that does not pose a problem for any other animal.*

  These functional constraints prevented the channel in the female’s pelvis from enlarging sufficiently to accommodate easily the continually growing size of her fetus’s brain during childbirth. Mother Nature devised numerous ingenious sleights of hand to thread the baby through the “eye” of a mother’s birth canal.† Despite these clever adaptations, hominid females began to experience increasingly difficult deliveries. The problem became especially acute around 150,000 years ago, at which point the hominid brain had completed a remarkably short burst of rapid inflation that had added one-third to its size. A disaster was in the making.

  Eventually, somewhere, sometime, a healthy young hominid had growing within her a new life whose head was simply too large to negotiate the confining walls of her birth canal. During the delivery, her baby became wedged. After a prolonged labor, she died. Her baby died. Those in attendance could do nothing to help. The laws of physics superseded the strength of her uterine contractions. Unfortunately, she was the first of an avalanche of young mothers to die. For the first time in the history of any higher animal, extraordinarily high numbers of healthy females began to die in childbirth; the percentage of stillbirths rose with the number of maternal deaths.

  The number of live progeny per mother at the outset of our species was low, because prolonged childhoods forced ancestral women to space their pregnancies far apart. Moreover, one child per pregnancy was the general rule. Young children who lost their mother during a subsequent delivery experienced a catastrophe. Their prospects of surviving without her were bleak. Even a small percentage of mothers dying in childbirth in each generation, especially when combined with factors like disease, drought, or predators, could have placed great stress on a local population.

  In a supreme paradox, the leading cause of death for females of the human species became birth. A cursory examination of dates on old gravestones in any cemetery prior to the twentieth century confirms the high mortality routinely associated with childbirth, a condition that does not exist for any other mammal. No female of any other species has as much difficulty bearing her young as a human. And no female of any other species routinely solicits and requires help from others to deliver her baby.*

  The death of the Unknown Mother signaled the onset of an evolutionary crisis. The loss of a significant number of mothers and their newborns in childbirth was a wasteful reproductive strategy that could have been expected to toll the death knell of the line. Yet it created precisely the kind of crucible in which a species must adapt—or die.

  Scientists working in the field of evolutionary biology hypothesize a mechanism to explain how a new species often seems to appear all at once in the fossil record. Imagine an isolated local population of an existing species living in harmony with its ecosystem. Suddenly, some new, harmful environmental factor impinges upon the system; large numbers of the local population begin to die. At the eleventh hour, a beneficial random mutation (or mutations) that had previously occurred in the genes of one individual increases its owner’s chances of surviving to the next generation.* The offspring of this fortunate individual inherit the gene (or genes) and it quickly spreads. Within the span of several generations, the hard-pressed local population that was on the verge of extinction surges back by evolving an innovative suite of internal metabolic adjustments, physical changes, or modified behavioral responses that allows it to adapt to its new circumstances.

  The animal to emerge sometimes differs so significantly from its predecessor that it can be categorized as an entirely new species. Scientists refer to this large dying off of the many so that the few (or even one) can evolve as “passing through a bottleneck.” When there is a sudden discontinuity between a precursor species and a new one, some scientists propose that this evolutionary process is due to what they call “punctuated equilibrium.”4

  Many conditions can precipitate bottlenecks. Geologic catastrophes, major volcanic eruptions, abrupt climatic changes (such as the sudden onset of ice ages), pluvials (periods of rains of Biblical proportions), and prolonged droughts can all position a species in the crosshairs of extinction. Epidemics of viruses, bacteria, or parasites can decimate food sources or attack the local population directly.

  Approximately 150,000 years ago, in a small region of East Africa, around present-day Uganda, Kenya, and Tanzania, the current countries bordering Lake Vi
ctoria, one such bottleneck occurred. A local population of Homo erectus, a tool-making hominid, had been living there successfully for over a million years.† Then some yet-to-be-identified event occurred that affected the survival of this particular group of hominids. From this stressed band, a single female known as Mitochondrial African Eve succeeded where Unknown Mother had failed, giving birth to the new species originally classified as Homo sapiens sapiens,* the doubly wise human.

  Though the exact birthdate of our species remains uncertain, the scenario that a single woman birthed the modern human species is on firmer scientific grounds thanks to the reliability of the new science of molecular biology.5 Laboratory tests performed on mitochondrial DNA can accurately measure the genetic variation that exists between members of a species and the differences existing among species. Scientists can then construct “molecular clocks” and calculate how long ago a particular species split away from its precursor.6 Molecular biology has proved to be the great Rosetta Stone of evolutionary changes. The existence of an African Eve is extremely likely, because the genetic material of all humans alive today is eerily similar.

  The genes of chimpanzee communities inhabiting ranges only a few thousand yards apart have more genetic diversity than those of humans separated by oceans. Despite the dramatic differences in the skin pigmentation, eye color, body shapes, and hair types of people from disparate regions of the world, all humans are genetically homogeneous to an extraordinary degree. In fact, there is less than 0.1 percent difference between the gene structure of any one human and another. This suggests that each of us is a not-so-distant descendant of one fairly recent ancestral female. Since we have not had time to diverge very far genetically, our species’ birthdate can be calculated backward in tens of thousands of years, instead of millions.

  Some dire factor, condition, or event adversely affected the species that lived in the area around present-day Lake Victoria, leading to a population bottleneck. Let us call it Factor X. But what was X? What environmental challenge could have been the catalyst for the radiation of a new species? The geologic and archeological record is relatively silent. Variations in the local climate did occur, but none seems harsh enough to prompt our origin. Scientists have not identified sudden discontinuities in the area’s flora or fauna. And yet some extreme condition must have occurred, for African Eve to burst forth like Athena fully formed from the brow of Zeus. Though there are many competing scientific theories, none has managed to gain sufficient support to explain the bottleneck fully.

  I propose that the “bottleneck” through which our unfortunate immediate ancestors squeezed was actually a real bottleneck. Scientists scouring the landscape in search of an external Factor X may have been looking in the wrong place. The precipitating event that pushed a local population of hominids toward the edge of extinction was neither a climate change, a geological force, the arrival of predators or disappearance of prey, nor a shift in the availability of food resources. It was an internal, anatomical one.*

  The unyielding walls of the birth canal, like the alignment of Scylla and Charybdis,† produced the bottleneck that shaped all subsequent hominid evolution. The death of the Unknown Mother and her unlucky baby, and the subsequent dying off of increasingly large numbers of hominid mothers and their newborns, was the stressful Factor X that precipitated the Homo sapiens line.

  The human female’s narrow pelvic canal combined with her fetus’s large head led to Homo sapiens’ “evolutionary bottleneck.”

  No other species has as difficult or dangerous a labor as a human does.

  Chapter 2

  Big Brain/Narrow Pelvis

  What men say of women is that we have a peaceful time

  Living at home, while they do the fighting in war.

  How wrong they are! I would very much rather stand

  Three times in the front of battle than bear one child.

  —Medea, the wronged wife of Jason, in Euripides’ play Medea

  The ninety-six hours or so following the onset of parturition (birth contractions) constitute the greatest period of mortality risk that a typical human will ever face.

  —Peter T. Ellison1

  Let us call African Eve’s adaptation to Factor X “Response W”—a clutch of mutations that remolded us into the most successful and disruptive large animal in the planet’s history. Molecular biologists have calculated that we share 95 percent to 98.4 percent of our species’ genes with our closest relative, the chimpanzee. (If we count only the active genes, the figure bumps up to 99.6 percent.) The slight reshuffling of the linear code in a small number of her genes must have set in motion changes that would result in innovative behaviors. These few genes transformed a relatively dull, plodding primate into a creature that was “something new under the sun.” The subtle reconfiguring of Eve’s genome would disperse her species to every continent and large island on the planet. Gracile humans, braving blizzards, would trudge north to inhabit frozen tundras. Others would sail fragile wooden boats across uncharted seas to populate hostile southern deserts.

  Our ancestors would then bring about the greatest mass extinction of large animals since the dinosaurs abruptly disappeared sixty-five million years ago. Through their ever-burgeoning technological prowess, humans would plant crops, tend herds, invent writing, build the Parthenon, discover gunpowder, transform the ceiling in the Sistine Chapel, compose the Eroica Symphony, and eventually evolve into a biological force capable of influencing the very climate of the earth. Eve’s descendants have steadily accumulated the power to destroy each other in an unholy Armageddon and, like sleepwalkers, are shuffling toward a planetary ecological disaster. How could a slight, five-foot-tall, two-legged animal create such sublimity and yet wreak so much havoc in so minuscule an interval of earth’s history?

  Contrary to what the intergalactic anthropologists witnessing the death of the Unknown Mother and the birth of African Eve would most likely have predicted, high maternal and infant mortality was not the beginning of the end. They would have predicted two different outcomes—ineffectively waddling, wider-hipped women, or smaller-brained, less intelligent babies—neither of which occurred. Instead of becoming extinct, we are now six billion strong and continue to multiply at a staggering rate. And yet, until quite recently, women continued to die in childbirth in alarmingly high numbers. How could this be? What possible benefit did having such large-brained babies confer upon the new species that could ultimately offset the significant percentage of fertile female deaths? Moreover, what changes wrought by African Eve’s few mutated genes with their minute DNA differences could have opened such an enormous chasm between us and our nearest chimp relatives?

  According to the available evidence painstakingly pieced together by paleoanthropologists from archeological sites, Response W was not a highly evolved consciousness, evidenced by the creation of art, musical instruments, burial rites, sewing needles, self-adornment, and sophisticated hunting techniques. These features appear much later. Some posit that it was the sudden maturation of our signature attribute, human language. There is little supporting evidence, however, that freshly minted humans mastered complex speech in the infancy of our species’ life cycle.

  What we know with certainty is that some subtle skeletal changes appeared: lighter, more delicate bones; a more commodious brain case; a flatter face; and a bigger larynx. But the most striking new feature was our balloon heads. The change in the size of the brain from erectus to sapiens seems to have occurred in an evolutionary instant. Early specimens of Homo erectus, our immediate predecessor, averaged a brain volume of nine hundred cubic centimeters. Our brain occupies, on average, fourteen hundred cubic centimeters. This one-third difference represents a huge increase in brain tissue over the astonishingly brief period of the last several hundred thousand years of erectus’s existence.

  The human brain is a very expensive organ to operate. Representing a mere 3 percent of total body weight, it can hungrily appropriate up to 25 percent of every he
artbeat’s oxygen-rich output. The brain demands that its owner expend considerable metabolic vigilance on its behalf. The concentration of ions (calcium, potassium, sodium, chloride, and magnesium) swirling in and around individual brain cells must hover in a very inflexible range. Both the brain’s pH and temperature must be narrowly regulated. The body’s waste-management system must constantly clear accumulating toxins from the rich soup in which the brain soaks.

  So why, we may ask, was such an oversized, extravagant organ installed in this one animal’s cranial pan? What was it doing at the outset to offset the high maternal death it caused? Many smaller-brained hominids seem to have successfully avoided becoming a big cat’s dinner for millions of years. If human language was perfected later, what was the selective pressure that favored a brain capable of such firepower?

  The enlarged brain does not appear to have led immediately to greatly superior techniques for acquiring food. That wasn’t necessary, for one of the earliest of the Homo line, the two-and-a-half-million-year-old Homo habilis (Handy Man and Handy Woman), seems to have been quite tenacious using his and her smaller brains. They, too, lasted nearly a million years before going extinct. The archeological record presents scant evidence as to why Homo habilis or the later Homo erectus evolved their crowning attribute.* Why, then, this big brain? The answer, I propose, has to do with sex, iron, and time.