Switching from four legs to two made many additional changes as well for humans

http://www.wsj.com/articles/first-steps-review-standing-on-our-own-two-feet-11623881597?

‘First Steps’ Review: Standing on Our Own Two Feet

When our ancestors made the switch from four legs to two, they freed up their hands—but there was an evolutionary price to pay.

PHOTO: ALAMY STOCK PHOTO

By David P. Barash

June 16, 2021 6:13 pm ETSAVEPRINTTEXT

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The list is long: How culture made us humanHow language made us human. Ditto for sociability, cooperation, religion, tools, consciousness, rationality, domestication, cooking, war, predation, child care, empathy, imagination and, of course, that perennial answer, God. To these, I am delighted to add walking. Jeremy DeSilva, an associate professor of anthropology at Dartmouth, makes the case in “First Steps: How Upright Walking Made Us Human.”

Mr. DeSilva, who specializes in paleoanthropology and anatomy, particularly the skeletal structure of the human foot and lower leg, will disabuse anyone who thinks that scientists who fuss around with old bones are tedious fossils themselves. Rather than trudging doggedly through the paths that eventuated in Homo sapiens, “First Steps” takes an adventurous, thoughtful and even joyous romp through its subject while proposing new views on our curious insistence on standing up for ourselves.

When my first child started to walk, I was entranced. When my second followed suit, I fantasized putting a brick in her diaper, having learned how difficult it is to care for a mobile primate. Why, then, do parents celebrate when their would-be toddler first begins to toddle? Quite possibly because there is something about walking upright that really does make us distinctly human. We are the only mammal that walks, jogs and runs on two legs—and, accordingly, we pride ourselves on standing tall.

Incorporating evidence from paleontology, physical anthropology, developmental psychology, molecular genetics and ecology, Mr. DeSilva strides confidently across some otherwise difficult conceptual and historical terrain, including the work of current researchers who have contributed to our understanding of when, why and how we reared up and stayed that way.

The book is rich in hitherto obscure insights: “A paleoanthropologist’s best digging tool is last season’s rain, which washes away sediment and gently exposes buried bone.” Mr. DeSilva’s recounting of how we became human is cleverly interwoven with a personal narrative concerning his own research trips, discoveries, and encounters with other paleoanthropologists. Along the way he gently exposes what we know, along with what we don’t.

FIRST STEPS

By Jeremy DeSilva
(Harper, 334 pages, $27.99)

In the hands of an expert, fossils can be eloquent. For example, the location of the foramen magnum, the opening in the skull for the spinal cord, reveals whether its possessor orients horizontally or vertically. Feet are also fluent: “First Steps” traces the arching curve that puts a spring in our step. We also get a fascinating look at prehuman Australopithecines—likely a mother and child—taking a stroll, a tale based on careful attention to fossilized footprints from 3.7 million years ago.


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“First Steps” has a colloquial tone that neatly obscures the fact that the author is trotting out some first-rate science, beginning with that most charismatic biped, T. rex. This upstanding critter benefited from a heavy tail; lacking such a counterbalance, we’ve been forced to fall forward as we walk, essentially catching ourselves with each step. Standing up has had medical disadvantages too: stresses on our spinal discs, often causing bulging, herniation and chronic pain; knees prone to trouble (walking shifts the body’s weight from side to side); and—most serious of all—the evolution of a bowl-shaped pelvis to undergird our viscera, which in turn has led to difficult, painful and sometimes lethal childbirth. The problem is known as “cephalopelvic disproportion”—when a large infant head encounters the unavoidable limits of a birth canal narrowed and twisted by our vertical posture. No other mammal has so much trouble giving birth. Evolution’s costs and benefits are inseparable; they march in lockstep even when it comes to something as upstanding as, well, standing up.

Mr. DeSilva notes that the costs of our two-footedness are potentially huge and that, by the standards of quadrupeds, even the fastest humans (Usain Bolt maxes out at 28 mph) are “pathetically slow-footed.” Bipeds are also prone to falls: The author cites statistics that put annual U.S. deaths from falling at 35,000—“nearly the same number who die in car accidents.” By contrast, he asks: “When’s the last time you saw a four-legged animal—a squirrel, dog, or cat—trip and fall?” And never mind the 700,000 knee replacements in the U.S. annually.

Why, then, are we so doggedly two-legged? We have lots of hypotheses, little certainty. Did the adaptation help in our peeping out above the Pleistocene savannah grasses? Probably not, given that the earliest prehuman bipeds were more forest-dwelling. Freeing our hands for tools and weapons? The problem with that notion is that the earliest prehuman bipeds (7 million years ago) preceded tools (3.3 million). Hand gestures and other signaling? Maybe. More likely: energetic efficiency, better thermoregulation and enhanced carrying capability.

When anthropologist Margaret Mead was asked to identify the first sign of civilized humanity, she reportedly replied that it would be a well-healed fossil femur, because for an early someone to have survived a serious broken leg, he or she would have needed substantial care from others. Mr. DeSilva proposes that the helplessness of frequently injured bipeds could have led to our “capacity for tolerance, cooperation, and caring for one another. Bipedalism in an overly aggressive ape with purely selfish tendencies and a low tolerance for other group members would have been a recipe for extinction.” A much-loved song from Rodgers and Hammerstein’s “Carousel” proclaims: “You’ll Never Walk Alone.” Maybe we never did.

Neil Armstrong described his 1969 lunar stroll as “one small step for [a] man; one giant leap for mankind.” Readers of “First Steps” will understand that humanity’s first steps, right here on Earth and however small, were a giant leap for all of us.

Mr. Barash is a professor of psychology emeritus at the University of Washington. His most recent book is “Threats: Intimidation and Its Discontents.”

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