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We walk, therefore we are

Lowly Origin: Where, When, and Why Our Ancestors First Stood Up, Jonathan Kingdon, Princeton University Press: 408 pp., $35

June 29, 2003|Donald Johanson | Donald Johanson is the author of numerous books, including "From Lucy to Language" (with Blake Edgar) and the forthcoming "The Skull of Australopithecus Afarensis."

Humans differ from all other primates, and indeed from virtually all other animals, in possessing a very weird adaptation. We don't think of it as weird because we do it every day of our lives. It is so obvious that when I ask my students what makes humans unique, many of them, after citing large brains and culture, miss the obvious: We walk on our hind legs.

Charles Darwin thought bipedalism, along with big brains and tools, was part of a package that defined us as human and emerged when our ancestors descended from their ancient arboreal habitat. Darwin suggested that uprightness liberated our hands from locomotor needs, thereby enabling our ancestors to make the tools that their big brains had visualized. This trinity of attributes began to unravel, however, when discoveries of the most ancient bipedal ancestors were found to possess small brains and apparently did not manufacture stone tools.

Anthropologists have grappled with this quandary for nearly a century, for there is scant doubt that our ancestors were walking on their hind legs at least 1.5 million years before they began crafting stone tools. This understanding prompted anthropologists to refocus their attention and consider why our ancestors exchanged a fast, stable, evolutionarily enduring four-legged mode of locomotion (quadrupedalism) for a slow, unsteady, disease-ridden (fallen arches, bad backs, hernias etc.) two-legged strategy. It certainly wasn't predestined that when our ancestors stood up, they would evolve into modern humans, but standing undoubtedly laid the groundwork. If reproductive success is a measure of the effect of a behavioral adaptation, then with more than 6 billion of us bipeds on the Earth today, this uncanny locomotor mode has had a big payoff.

(During my days as an undergraduate, I learned that our ancestors stood up to look over the tall savanna grass. And yet I had to wonder: What was the survival rate for a short, indefensible, small-brained ancestor, like Lucy and her ilk, after standing up to look over tall grass, thus announcing their presence to every hungry carnivore in the neighborhood, all of which were quadrupedal and very fast? Evolutionary success is about leaving genes, but the Savanna Hypothesis, as it came to be known, is really nothing more than a quick route to extinction.)

Jonathan Kingdon is uniquely skilled to embrace the daunting task of learning how we became human because of his intimate lifelong affair with Africa. Brought up in Tanganyika (now Tanzania) and sensing the pulse of Africa as a barefoot youth, he nourished his curiosity on a never-ending diet of close encounters in the crucible of human origins. The real message from Kingdon's book, "Lowly Origin," is that hominid fossils are only a part of the story. Thus, Kingdon ponders the origins of our singular adaptation within a richly textured framework of African animal behavior, geography and ecology.

Kingdon rejects single-cause explanations for upright walking, such as looking over tall grass, reaching up into trees for fruit, carrying food etc. Instead he proffers a scenario that paints a more nuanced picture of early hominid ancestors moving to the ground to exploit rich food sources. Couching his argument in a classic Darwinian framework of gradual evolutionary change, he outlines a more credible series of sequential postural and feeding adaptations that ultimately led to bipedal posture and locomotion.

Kingdon's scenario will elicit widespread discussion. He contends that it was in eastern Africa and especially in the forests adjacent to the Indian Ocean that our ancestors experienced the primal glimmerings of uprightness. He envisions this process not as a rapid happening but as a gradual postural adaptation from having lived as ground apes and having incorporated a squat feeding phase, which is characterized by increasing verticality of the body as a precursor to bipedalism. It was the acquisition of uprightness, freeing the forelimbs and hands from locomotor tasks that set the stage for human modernity.

Kingdon's model is decisively rooted in the ecology and biogeography of Africa's past. He cleverly interweaves his firsthand insights into the behavior and adaptations not only of modern African primates like the great apes and monkeys but also of the other African mammals in the larger arena of evolution. With his unsurpassed knowledge of Africa, Kingdon views us not as having evolved from ape to angel but as having lived as "just another African mammal" in a rich ecological setting through a series of astonishingly successful behavioral adaptations.

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