Dozens of scientists have interpreted her bones, reconstructed her flesh, her gait, her sex life, in dozens of different ways and argued over whether she walked well or poorly. Discovery conveys a certain privilege of interpretation, and so Johanson, who worked at the Cleveland Museum, took the bones he found in Hadar, Ethiopia, to his friend Owen Lovejoy, an anatomist at Cleveland State University and an expert on human locomotion. Lovejoy issued the orthodox verdict. In his book Lucy, Johanson reports that Lovejoy said of the afarensis knee joint he had brought in the year before,
“This is like a modern knee joint. This little midget was fully bipedal.”
“But could he walk upright?” I persisted.
“My friend, he could walk upright. Explain to him what a hamburger was and he’d beat you to the nearest McDonald’s nine times out of ten.”
Johanson’s knee joint came along as the first material support for Lovejoy’s bold theory that bipedalism had begun and been perfected far earlier than anyone else had assumed. The following year, the Lucy skeleton—or the 40 percent of it that was recovered—further confirmed his hypothesis about the antiquity of human walking, as did the 3.7-million-year-old footprints of a pair of walkers Mary Leakey’s team found at Laetoli, Tanzania, in 1977. But why had these creatures become bipedal?
By 1981 Lovejoy had evolved a complicated explanation for why we got up and walked. His 1981 Science article “The Origin of Man” has become the focal point for the arguments in the field about the reasons why walking appeared 4 million or more years ago. Lovejoy evolved an elaborate thesis that decreasing the time between births would increase the survival rate of the species. “In most primate species,” he wrote, “male fitness is largely determined by consort success of one sort or another”—that is, in the ability or opportunity to mate and thereby pass along their genes. He proposed that in the Miocene era, 5 million and more years ago, the human ancestor changed its—or rather his—behavior. Males, he proposed, began to bring back provisions for the females; the females thus provided for were able to bear more children as the challenge of feeding themselves and their young was lessened, and the male-headed nuclear family was born. In other words, male fitness had expanded to include provisioning, which would allow them to pass along those genes more frequently and certainly. “Bipedalism,” he wrote in a 1988 summary, “figured in this new reproductive scheme because by freeing the hands it made it possible for the male to carry food gathered far from his mate.” But, he added, such daily separation of the sexes would only genetically favor males if they could come home and propagate their own genes and no one else’s—thus the behavior must have selected for monogamous females as well as responsible males. Lovejoy explained, “The highly unusual sexual behavior of man may now be brought into focus. Human females are continually sexually receptive and . . . male approach may be considered equally stable.” Since unlike the females of most species this one no longer signaled her fertile times, they had sex a lot to procreate and to bond. If we regard it as a creation myth, it is one in which the two-parent family is far older than the human species, hominid males are mobile and responsible partners and parents, and females are needy, faithful, stay-at-home mates who are not the instruments of bipedal evolution.
The 1960s myth of Man the Hunter had been succeeded by two theories in the 1970s. One dubbed Woman the Gatherer proposed that the primordial diet was probably mostly vegetarian and was mostly collected then, as in hunter-gatherer societies today, by females. The other emphasized food sharing as instrumental in ensuring survival and generating a home base to which food was brought and shared, resulting in more complex social consciousness. In this theory, a communitarian First Supper takes the place of Ardrey’s blood sports as the event that propelled us into humanity. Lovejoy combined aspects of both these new theories to create his Man the Gatherer, who brought food home and shared it, though only with his mate and offspring. His theory suggested not only that walking had been a male business, and that the males in question had been full of family virtues, but that the virtues in question had made us walkers. In fact, he said, Lucy and her ilk could walk better than we do, and further, the species had lost its ability to climb.
I was staying with Pat in his shack just outside Joshua Tree National Park while I wrote this chapter. Preoccupied and trying to sort out the sea of material before me, I kept recounting theories to him about why we became bipedal, about details of anatomy and function, and he laughed incredulously at the more outlandish ones. “People get grants and tenure for that?” he’d say. His favorite was R. D. Guthrie’s 1974 proposal that when hominids became bipedal, the males used their now-exposed penises as a “threat display organ” to intimidate opponents, and we speculated on the origins of human laughter. The following day, after he came home from guiding clients up and down rock faces all day and was lounging with a drink, I read him anthropologist Dean Falk’s attack on Lovejoy. Lovejoy’s term “copulatory vigilance” caught his attention, and he laughed more at the strange stuff I was immersed in. Not that his world was exactly a bastion of seriousness: while he was climbing for pleasure the day before, I had lain in the shade idly flipping through his guidebook and been entertained by some of the names of the climbing routes up and down the park’s myriad giant boulders: “Presbyterian Dental Floss” was right next to “Episcopalian Toothpick,” while “Boogers on a Lampshade” mocked the climb genteelly called “Figures in a Landscape,” and innumerable poodle, political, and anatomical jokes described other vertical routes up the rocks. That evening, as I read bipedal theory to him and the quail bobbed about the backyard and the setting sun pushed the shadows of the hills farther and farther across the valley, he swore he would get his friends who founded and named many of the park’s climbing routes to name the next one “Copulatory Vigilance,” an obscure monument to a theory that we had lost our ability to climb and to his opinion of the more far-flung theories of human origins. Lovejoy’s theory has become famous, if only because no one can resist attacking it.
Among the earlier critics were the anatomists Jack Stern and Randall Sussman at the State University of New York at Stonybrook, who I visited. Two unathletic men with identical clipped gray mustaches, they looked something like the Walrus and the Carpenter, with Stern as the compact Carpenter and Sussman the expansive Walrus. They talked to me for hours in an office full of bones and books, and periodically one or the other would grab a chimp pelvis or a cast of a fossil femur to illustrate a point. Obviously enthusiastic about their work, they often went off on conversational tangents with each other that left me far behind, and they delighted too in dishing their colleagues in this contentious field. They had argued that Johanson’s Lucy-era Australopithecus afarensis fossils were those of apprentice walkers who, based on the evidence—big arms and smallish legs, curved fingers and toes—continued climbing trees well and frequently for a long time afterward. Another feature of the afarensis fossils they took up was gender size: if the large and small skeletons Johanson and company had found in Ethiopia were the same species (which Richard Leakey and others contest), then the sizes must represent small females and large males, which made it unlikely they practiced Lovejoy’s monogamous arrangement. Living primate species where the males are far larger—baboons, gorillas—are usually polygamous; only those without size differences, such as gibbons, are monogamous. So their version of Lucy was that she was a lousy walker with big floppy feet, a pretty good climber with long, strong arms, and probably part of a polygamous group in which small females spent more time in the trees than large males.
Sussman said, “Back when we started this work, and I don’t think it’s unhumble to say it, the majority of the people in the field would say we evolved in the savannah, in the open country of the veldt of South Africa or the savannah of East Africa. I think that’s a load of crap. I think that what happened was that afarensis was living in forest and open country mosaics like you see today in places like the French Congo or along rivers where there’s a
lot of trees. I mean, that probably went on for a million years when you had an animal that was climbing and an apprentice biped.” He added that in the old pictures re-creating this phase of evolution, the creatures were strolling across the grassland; newer ones showed them in much more mixed habitat, and the most recent National Geographic articles had paintings that placed these creatures in forests with some of them in the trees. That the creatures were forest dwellers and tree climbers had become, Stern said, so obvious that no one bothered to credit Stern and Sussman for pushing the idea early on.
The argument before had been circular: that hominids had learned to walk in order to venture onto the savannah, and that if they survived on the savannah, they must have been competent walkers. And the savannah seemed to be an image of freedom, of unlimited space in which the possibilities were likewise unlimited, a nobler space than the primeval forest that was less like the open forest of Rousseau’s solitary wanderers and more like the jungles from which Jane Goodall and Dian Fossey sent back their primate reports. Stern said a little later on, “I worry most about the manner of their bipedal walking. I wrote a paper saying they could not have walked as we do. It’s not fast, it’s not energetically efficient. . . . Are we wrong? Was their method of bipedalism actually pretty good?” Sussman cut in, “Or did they combine very good tree-climbing with shitty bipedalism and gradually the proportions reversed . . .” Stern continued, “The argument that I sometimes soothe myself with is that chimpanzees are really pretty crappy quadrupeds themselves, as four-footed animals go. So if they can be pretty crappy quadrupeds for seven million years, then we could’ve been pretty crappy bipeds for a couple of million years.”
At the 1991 Conference on the Origins of Bipedalism in Paris, three anthropologists had reviewed all the current theories on walking as a kind of academic stand-up comedy routine. They described the “schlepp hypothesis,” which explained walking as an adaptation for carrying food, babies, and various other things; “the peek-a-boo hypothesis,” which involved standing up to see over the grass of the savannah; “the trench coat hypothesis,” which, like Guthrie’s theory that so amused Pat, connected bipedalism to penile display, only this time to impress females rather than intimidate other males; “the all wet hypothesis,” which involved wading and swimming during a proposed aquatic phase of evolution; “the tagalong hypothesis,” which involved following migratory herds across that ever-popular savannah; “the hot to trot hypothesis,” which was one of the more seriously reasoned theories, claiming that bipedalism limited solar exposure in the tropical midday sun and thus freed the species up to move into hot, open habitat; and the “two feet are better than four” hypothesis, which proposes that bipedalism was more energy-efficient than quadrupedalism, at least for the primates who would become humans.
It was quite a collection of theories, though since talking to Stern and Sussman I had grown accustomed to the fluctuating interpretations of what to a lay person exposed to only one source sounds like established fact. The bones unearthed in Africa in ever greater quantity remain enigmatic in crucial ways, and the business of their interpretation recalls the ancient Greeks reading the entrails of animals to divine the future, or the Chinese throwing I Ching sticks to understand the world. They are constantly being rearranged to correspond to a new evolutionary family tree, a new set of measurements. Two Zurich anthropologists, for example, recently declared that the famous Lucy skeleton is actually that of a male, while Falk argues that she is not a human ancestor. Paleontology sometimes seems like a courtroom full of lawyers, each waving around evidence that confirms their hypotheses and ignoring the evidence that contradicts it (though Stern and Sussman impressed me as being exceptionally committed to evidence rather than ideology). Only one thing seemed agreed upon in all these competing stories of the bones, the thing that Mary Leakey had said when she wrote about the footprints her team had found in Laetoli: “One cannot overemphasize the role of bipedalism in hominid development. It stands as perhaps the salient point that differentiates the forebears of man from other primates. This unique ability freed the hands for myriad possibilities—carrying, tool-making, intricate manipulation. From this single development, in fact, stems all modern technology. Somewhat oversimplified, the formula holds that this new freedom of forelimbs posed a challenge. The brain expanded to meet it. And mankind was formed.”
Falk wrote the most devastating reply to Lovejoy’s hypothesis in a 1997 essay titled “Brain Evolution in Human Females: An Answer to Mr. Lovejoy.” She declared, “According to this view, early hominid females were left not only four-footed, pregnant, hungry and in fear of too much exercise in a central core area, they were also left ‘waiting for their man.’ ” And she went on to say, after reviewing details such as the unlikelihood of monogamy between such differently scaled males and females, to comment, “The Lovejoy hypothesis may also be viewed at an entirely different level, i.e., as being preoccupied with questions/anxieties about male sexuality. At its most basic level, the hypothesis focuses on the evolution of how men got/get sex.” She goes on to point out that the behavior of terrestrial female primates suggests that female ancestral hominids chose multiple partners for reproductive and recreational sex, and “much of the world appears to fear that this might still be the case as indicated by the universal close observation and control of sexual conduct in human communities, not to mention all those male insecurities simmering beneath the surface of Lovejoy’s hypothesis.”
Having dismissed the notion that a providing male brought home the bacon to a monogamous, immobilized mate, Falk took up the alternate and much simpler theory that walking upright minimized the amount of direct sun the earliest hominids received as they moved in the open spaces between patches of trees, thereby freeing them to move farther and farther out from the shade of the forest. Falk explains that Peter Wheeler, whose hypothesis it was, proposed that “these features led to ‘whole-body cooling’ that regulated temperature of blood circulating to (among other regions) the brain, helped prevent heatstroke, and thereby released a physiological constraint on brain size in Homo.” Thus the changes freed the species to grow larger and larger brains, as well as to wander farther and farther. She buttresses Wheeler’s theory with information drawn from her own research into brain evolution and structure and concludes, as Mary Leakey did, though for a different reason, that becoming upright walkers didn’t create but did make possible the rise of intelligence.
Intelligence may be located in the brain, but it affects other parts of the anatomy. Consider the pelvis as a secret theater where thinking and walking meet and, according to some anatomists, conflict. One of the most elegant and complicated parts of the skeleton, it is also one of the hardest to perceive, shrouded as it is in flesh, orifices, and preoccupations. The pelvis of all other primates is a long vertical structure that rises nearly to the rib cage and is flattish from back to front. The hip joints are close together, the birth canal opens backward, and the whole bony slab faces down when the ape is in its usual posture, as do the pelvises of most quadrupeds. The human pelvis has tilted up to cradle the viscera and support the weight of the upright body, becoming a shallow vase from which the stem of the waist rises. It is comparatively short and broad, with wide-set hip joints. This width and the abductor muscles that extend from the iliac crests—the bone on each side that sweeps around toward the front of the body just below the navel—steady the body as it walks. The birth canal points downward, and the whole pelvis is, from the obstetrical point of view, a kind of funnel through which babies fall—though this fall is one of the most difficult of human falls. If there is a part of anatomical evolution that recalls Genesis, it is the pelvis and the curse, “In sorrow thou shalt bring forth children.”
Giving birth for apes, as for most mammals, is a relatively simple process, but for humans it is difficult and occasionally fatal for mother and child. As hominids evolved, their birth canals became smaller, but as humans have evolved, their brains have grown larger and large
r. At birth the human infant’s head, already containing a brain as big as that of an adult chimpanzee, strains the capacity of this bony theater. To exit, it must corkscrew down the birth canal, now facing forward, now sideways, now backward. The pregnant woman’s body has already increased pelvic capacity by manufacturing hormones that soften the ligaments binding the pelvis together, and toward the end of pregnancy the cartilage of the pubic bone separates. Often these transformations make walking more difficult during and after giving birth. It has been argued that the limitation on our intelligence is the capacity of the pelvis to accommodate the infant’s head, or contrarily that the limitation on our mobility is the need for the pelvis to accommodate birth. Some go further to say that the adaptation of the female pelvis to large-headed babies makes women worse walkers than men, or makes all of us worse walkers than our small-brained ancestors. The belief that women walk worse is widespread throughout the literature of human evolution. It seems to be another hangover from Genesis, the idea that women brought a fatal curse to the species, or that they were mere helpmeets along the evolutionary route, or that if walking is related to both thinking and freedom, they have or deserve less of each. If learning to walk freed the species—to travel to new places, to take up new practices, to think—then the freedom of women has often been associated with sexuality, a sexuality that needs to be controlled and contained. But this is morality, not physiology.
I got so annoyed by the ambiguous record on gender and walking that early one fine morning in Joshua Tree, while the cottontails were hopping in the yard, I called up Owen Lovejoy. He pointed to some differences between male and female anatomy that, he said, ought to make women’s pelvises less well adapted to walking. “Mechanically,” he said, “women are less advantaged.” Well, I pressed, do these differences actually make a practical difference? No, he conceded, “it has no effect on their walking ability at all,” and I walked back out into the sunshine to admire a huge desert tortoise munching on the prickly pear in the driveway. Stern and Sussman had laughed when I asked them whether women were indeed worse walkers and said that as far as they knew, no one had ever done the scientific experiments that would back up this assertion. Great runners tend to converge in certain body types, whichever gender they are, they ruminated, but walking is not running, and the question of what constitutes greatness there is more ambiguous. What, they asked, does better mean? Faster? More efficient? Humans are slow animals, they said, and what we excel at is distance, sustaining a pace for hours or days.
Wanderlust: A History of Walking Page 6