The walking way

The walking way – evolution of bipedal walking

Marcelo Games

Bipedal walking has been with us, has characterized our kind since the proposed evolutionary beginning

MOST PEOPLE WALK EVERY DAY, SEVERAL TIMES A DAY, AND IN SEVERAL DIFFERENT CONTEXTS. WE WALK IN AND OUT, TO AND FROM, OVER AND UNDER, AROUND, ABOUT, AND BETWEEN. IT’S SORT OF LIKE BREATHING–WE DO IT SO OFTEN AND IT comes so naturally that we don’t even think about it. But if we did think about it, we would soon realize that simple, everyday, run-of-the-mill, bipedal walking is among the most crucial and defining elements of human nature. Humans, in fact, are the only mammals on Earth designed to walk in a habitually upright position, using only the hind limbs for locomotion while releasing the forelimbs to a myriad of “extralocomotor” activities. Not even the Great Apes, our closest living relatives, can lay claim to this particular eccentricity. So unique is the notion and the architecture of bipedal walking that it may very well be the hallmark of our species: We are, in essence, the way we walk.

In the early days of anthropology, back at the turn of the century when Drawinism was shedding its baby teeth and naturalists-cum-anthropologists had begun in earnest the process of full-blown public deliberation over the origins of humanity, the major consensus was that the development of a large brain had been the principal factor in the establishment of the human species. For years, scholars considered intelligence–abstraction, language, consciousness–to be the evolutionary guide to human uniqueness.

The argument began roughly as follows: If human beings evolved from a common apelike ancestor, and human beings are most visibly distinguished from apes by their high level of physical, technological, and intellectual sophistication, it follows that some major adaptive element, such as brain growth, must have been selected to initiate this distinction.

The physical evidence for an early human ancestry, which at the turn of the century indicated a prehistory of perhaps 800,000 years, consisted primarily of skulls, skull fragments, teeth, upper-leg bones, stone tools, and living sites, all of which suggested a big-brained, tool-manufacturing, upright-walking, relatively intelligent humanlike ancestor. Somehow, for whatever reasons, our earliest representatives developed uncommonly large brains, which sparked creativity and invention, and which, in turn, ignited technology.

Technology required manipulation and precision, and what better than the ever-versatile primate fingers to manipulate precisely? The fingers, hands, and arms, now busy with the manipulating of technology, could no longer be used for walking–hence, the development of bipedal locomotion and all the rest of what would come to characterize the human form. Intelligence, the scholars concluded, was the crucial motivating factor in the divergence of human from the rest of the animal kingdom.

Ironically, intelligence has all but proven itself a byproduct, the result of a far deeper structural variation of an otherwise common primate mold. In 1925, the notion of brain growth as the seed of human fruition received the first official challenge to its credibility. An anatomist named Raymond Dart announced the discovery of an apelike-humanlike skull far more primitive than anything yet recorded and endowed with an embarrassingly tiny noggin. Key to Dart’s assessment of the skull’s “humanness” (as opposed to “apeness”) was the location of a very special hole at the base.

This hole, a common feature at the bottom of every skull, the entryway of the spinal cord to the brain, is the pinnacle upon which the head is balanced in relation to the body. It is called the foramen magnum, and it may well be the most telltale clue as to the humanness of an otherwise questionable cranium. Only in humans, apart from all the other primates with whom we share the same basic anatomical machinery, is the foramen magnum centered in the skull so that the head rests upon a vertical midline. This placement is the function, the result, the calling card of bipedal locomotion.

Most mammals are quadrupedal (four-legged) or, in some cases, quadrumanal, as in arboreal monkeys who use all fours to climb and swing and leap. The “locomotor apparatus”–the spinal column in association with the skull, pelvis, and limbs–is typically designed like a bridge with four legs. Basically, the spinal column spans from the neck to the pelvis in a slight arch so that weight and gravity are absorbed and displaced along a horizontal train of more or less equally sized vertebrae. The foramen magnum in these animals is located near the back of the skull so that the head “hangs” from the neck like the scoop of a backhoe. The pelvis is long and narrow and lies at an angle to the femur (thigh bone) so that the hip joint lies behind and below the horizontal midline, directly across from and parallel to the forelimbs.

In humans, the locomotor apparatus is designed like a column. At the top, the spine begins with a single outward arch but gradually curves inward toward the lumbar region (lower back) to form a second arch, thus moving the midline of the trunk forward so that it is centered, along with the skull and forelimbs, directly above the hip joint. Weight and gravity, therefore, are absorbed and displaced along a vertical continuum of gradually enlarging vertebrae. The skull balances rather than projects. The pelvis, shortened and flared like the wings of a butterfly, is aligned with the femur and lies beneath and around the midline. The human walks upright, stacked like a tower rather than extended like a clothesline.

Dart was able to identify the humanoid, or hominid, positioning of the foramen magnum as well as several hominid dental characteristics on the ancient skull he recovered from Africa’s distant past. Citing this evidence and the fact that the brain was no larger than a chimpanzee’s, he proposed that the human walking mode–the blueprint for bipedality–not the growth of gray matter had been the first true “gait” to the grand fluroscence of humankind. The skull was that of a mere child, however, and, perhaps because adults seem always to know best, critics dismissed its importance, reminding Dart that even in the modern world, the distinguishing features observed between adult humans and chimpanzees are fuzzy until they develop into adolescents.

In addition, Dart could offer only one example of this supposed “humanape”; far more evidence would be needed to substantiate his claim. The little skull was deemed indeterminate, and the budding world of anthropology happily turned its large brain away from Dart and the audacious suggestion that intelligence might not be the root of human uniqueness. It was only a matter of time, of course, before curiosity turned up more of Dart’s humanapes–adults, no less, and still lacking in brain development what they more than made up for in bipedal architecture. Included among the supporting evidence were teeth, skulls, vertebrae, leg- and arm-bone fragments, pelvic fragments, and the very crucial pieces–parts of feet.

The foot, to divert for a moment, like the foramen magnum, spinal column, and pelvis, is a major signifier of bipedalism. Like the pelvis, it has been reshaped or molded to accommodate the otherwise awkward two-legged gait. In all primates, minus humans, the foot is designed much like the hand–and quite rightly, seeing that both are utilized for the same basic purposes: walking, climbing, grasping. In the common primate foot, therefore, the big toe, like the thumb of the hand, is separated from the other toes and is highly flexible or “opposable.”

In humans, because weight has been transferred to the vertical midline and centered through the pelvis, along the legs, and down to the feet, the big toe has become an important stabilizer to the successful execution of the bidepal stride. The stride, or gait, is composed of a series of skeletomuscular actions (heel-strike, flat-foot, toe-off) which combine to produce two major phases of motion–stance and swing–each occurring simultaneously between the two legs. The stance phase occurs in the leg supporting the body as the other, in swing phase, moves forward to take over. Stance begins with the heel-strike; body weight moves across the heel, along the outer edge of the foot (flat-foot), and then inward to the ball of the foot and the big toe where toe-off occurs, and the body is propelled in a forward direction. Swing phase begins with toe-off and proceeds through a series of muscular contractions that swing the leg forward, pulling up the knee and pivoting the body around the stance leg forward the end of the swing and the beginning of a new step (heel-strike, flat-foot, toe-off).

The human walks or “strides” with a relatively smooth, straight, and balanced flow, while an ape in the upright position waddles from side to side and tends to lurch forward to where gravity tugs at its midline. Dart’s humanapes, at first glance, probably looked and acted very much like an odd strain of chimpanzee or gorilla, but deep inside, beneath the flesh of outward appearance, they held the secret formula, it seems, to the pathway of human development. He dubbed this 2- to 3-million-year-old ancestral contender Australopithecus africanus, and the rest is, shall we say, prehistory?

Not only did Dart’s and subsequent discoveries reveal that the human species was far older than had previously been considered, it also implied that long before big brains and superior intelligence acquired the reins of our planetary destiny, early human prototypes were walking, for whatever reasons, much the same way we walk today in all our highbrowed splendor. Bipedal walking has been with us, has characterized our kind since the proposal evolutionary beginning, since those fateful moments when we climbed down from the trees and took to striding freely along the broad, sun-drenched savannas of the African frontier.

Consider the relative ease with which we acquire the ability to walk. It’s like learning to speak–a function clearly associated with the superior intellectual capacity of the human brain. Like speaking, walking is a learned behavior that involves the mastering of a standard complex of built-in response mechanisms, in this case stemming from the motor and sensory regions of the cerebral cortex. The capacity for walking, like that of language acquisition, is no accident. It is the result of perhaps millions of years of biological adaptation and genetic selection. The capacity, in other words, is specified in the very design of the human structure. The individual’s job, usually in the toddler stage, is to figure out how to use it, generally through the process of trial and error like we do everything else. By the time we reach adulthood, walking has become such an intrinsic part of our everyday routine that, like breathing (and to a certain extent, speaking), we tend to take it completely for granted. The way we walk becomes as much a part of our individual identify as the timbre of our voices–distinct, perceptual reflections of who we are and how we happen to be feeling at any given moment.

The question of what came first in human origins remains a sizzling topic of controversy in the forefront of anthropological research. The implications range from dental gaps to gender gaps and seem constantly to fluctuate between the swirling folds of our own generation gaps. We will never know the exact sequence of events which led to our formation. If we did–if we had, for instance, all the facts right before our noses–we would probably fail to agree on their precise arrangement.

We can, however, agree on certain highly consistent physical markers such as the architecture of bipedalism and the measure of brain growth, and we can place them in a rough chronology based on solid evidence and hightech verification methods. In this context, we can safely determine that although it may not be the single evolutionary key to a human-from-apelike divergence, habitual bipedal walkability is certainly one of the most crucial notches in the doorjamb and became so long before consciousness could account for it.

Today we live in the aura of our intellectual achievement. We drive in automobiles; fly in airplanes; create arbitrary worlds in pictures, sounds, and words, and even computer programs. We design great cities and live in complex dwellings replete with electricity, plumbing, heat, and refrigeration, and yet we who walk bipedally do so in ways and amounts that elude our conscious perception. We are in constant motion: perpetual two-legged verbs engaged in the occupation of carrying out the sentences of our experience across the landscape of evolution.

And while we drive our automobiles, peck at the keys of fantastic computers, and design great buildings to house our intellectual geniuses, we never stray too far from the context of those two unparalleled columns of human eccentricity. We are all–brilliant, mundane, healthy, or ill–inextricably linked forever by the footfalls of our own primordial design.

COPYRIGHT 1993 Omni Publications International Ltd.

COPYRIGHT 2004 Gale Group