Chapter 1 of Sex, Time and Power
An excerpt...  

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 Santayana

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 Washburn

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.”

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 Victoria, 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. 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. 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 muscles making up the human pelvic floor formerly served the genial function of wagging animals’ tails. Natural Selection urgently pressed what was left of them into a new use in the bipedal hominid. They now served to buttress a potentially lethal defect. Some intermittently upright animals—for example, penguins—have evolved similar adaptations to defend against this problem, but in no other species is the gravitational hazard as serious as it is in humans.

†The soft bones of a human baby’s skull resemble tectonic plates. As the infant’s head wends its way down the mother’s tortuous birth canal, the plates slide and bend to conform to each twist and turn. To assist this molding process, the bony circle of the mother’s birth canal relaxes. Under normal conditions, the iliac, pubic, ischial, and sacral bones are welded together by dense bridges of cartilage nearly as rigid as the bones they join. During delivery, however, this tissue undergoes a remarkable transformation, akin to concrete dissolving into Silly Putty. As the fetal head progresses, the pelvic circle, in a complementary maneuver, stretches imperceptibly, its new elasticity conveniently conforming to the mush-skull pushing through it.

*There have been sightings of dolphins and whales attempting to assist pregnant females of their kind with deliveries. In one spectacular example observed in captivity, three different species of dolphins were involved. A full-term female was in trouble: Her newborn’s dorsal fin was caught in her pelvis. The second dolphin pulled out the baby and assisted the mother to raise it to the surface. While this was happening, the third female delivered the afterbirth, using her teeth. A few land mammals, such as rodents and primates, may also offer limited assistance to a female in labor. Despite these isolated reports, what is clear from observations of many animal births is that no other species’ full-term females routinely signal their need for birth assistance. Contrary to popular myths, indigenous women do not simply go into the field and bear their babies alone. In a cross-cultural study of 296 peoples, only 24 reported that a woman on occasion has her baby without assistance. In none of the cultures studied was an unassisted first birth a routine event.

*A single gene’s sequence of DNA contains the instructions for how to build a protein, which in turn can become an enzyme that further directs the building of an organism. Since there are many variations on the 3-D configuration of proteins and the timing of their entry into the building schedule, a single gene can have an enormous impact on the final form, metabolism, and responses of an organism.

†To avoid a clutter of scientific terms, I will gloss over the subtle distinctions between the fossils referred to as Homo heidelbergensis, Homo ergaster, archaic Homo sapiens, and many other recent paleontological finds. Each new detail gleaned from studying these ancient bones adds incrementally to our understanding of the evolution of our species, but, unfortunately, to do the subject justice would, I believe, distract from my narrative. Also, a species can evolve in response to a positive development in its environment. A new untapped food source, for example, can prod a species into evolving novel adaptations to take advantage of the bounty. I conjecture that the dominant influence affecting our species was a negative one rather than a positive one, however.

*This term is now outmoded. With the recent identification of Neanderthal DNA, it is no longer necessary to call us Homo sapiens sapiens, except for occasional emphasis. For the rest of this book, I will use the current classification of our species, Homo sapiens.

*This is the “obstetrical dilemma” first described by Sherwood Washburn in 1960 and elaborated by others, particularly Wenda Trevathan and Karen Rosenberg. The major focus in the literature has been on the effect of difficult labor on child development. The narrowness of the human female pelvis caused infants to be born alitricial—that is, extremely immature. According to estimates based on the size of other primate infants, the length of a human pregnancy should be eighteen months instead of nine. Bringing infants into the world long “before their time” created unique survival problems.

Helpless babies imposed immense child-rearing responsibilities on mothers, forcing a drastic division of labor between the human sexes. And it required women to enjoin men to assist them in raising their offspring, since failure in this endeavor would have fatal consequences for the entire species. It also created novel opportunities for children to have a longer period, called childhood, in which to learn. Much has been written about the consequences of the prolonged human childhood. I wish to redirect the focus away from immature infants to what I consider to be a relatively neglected aspect of the human species’ obstetrical dilemma—namely, maternal mortality.

†From a Greek myth, Scylla and Charybdis were two dangerous obstacles between which Odysseus’ ship had to navigate during the odyssey.

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