How “Round Round Get Around” Made Us Human
Posted by Richard Conniff on February 29, 2016
For the Wall Street Journal, I reviewed Restless Creatures: The Story of Life in Ten Movements by Matthew Wilkinson:
Roughly 100 million years ago, in the mid-Cretaceous, a pterosaur with a spoonbill and a 16-foot wingspan dominated the skies over what is now eastern England. How did it fly? Or, more to the point, how did it get into the air in the first place? As a doctoral student at the University of Cambridge in the 1990s, zoologist Matt Wilkinson set out to answer these questions, with the help of reconstructions and wind-tunnel tests.
Anhanguera, the pterosaur he studied, would have weighed just 22 pounds, making it surprisingly light for such a large creature and well suited to staying aloft on rising warm-air currents. But its anatomy indicated that it could not manage the wing flapping necessary for takeoff. Mr. Wilkinson concluded that it must have relied on a combination of gravity and abundant thermals to become airborne, meaning that it probably plunged into the air, like modern frigate birds, from seaside cliffs.
“This experience was to be my epiphany,” Mr. Wilkinson writes in his often intriguing but ultimately flightless “Restless Creatures: The Story of Life in Ten Movements.” “I would never look at the world in the same way again, for once accustomed to a locomotory point of view I realized that flight is not unique in its power to shape adaptation. On the contrary—I began to see the guiding hand of locomotion everywhere I looked. Thanks to Anhanguera I had stumbled upon life’s big secret, hiding in plain sight.” That secret was that locomotion—the business of getting from one place to another—“has dominated evolutionary possibility from the very outset.”
Although this sounds like an audacious proposition, Mr. Wilkinson evidently means it. He starts out by lamenting that evolution by natural selection has come to seem like “the one and only answer to any question about life.” Though “sort of true,” he continues, “pointing at a single element in a causal chain hardly amounts to an intellectually satisfying explanation.” The randomness of natural selection also leaves us with the dispiriting idea of evolution as just “one damned thing after another.”
This is, of course, much too bold a start. Natural selection is hardly a “single element” in a causal chain but a collective term for a host of factors—like predation, weather, disease, hunger, competition and sexual (largely female) choice—that favor some traits and weed out others. Moreover, Charles Darwin himself included locomotion among those factors, arguing, for instance, that our own upright bipedal posture had been gradually favored in early human ancestors as forest habitat gave way to open savanna. But never mind all that. If we can set aside the opening flurry with Darwin, Mr. Wilkinson’s argument that locomotion provides “a way of making deeper sense of ourselves and other living things” begins to seem persuasive.
In describing the evolution of the human form, for example, he starts by pointing out that opposable thumbs, “though often casually held up as key human accoutrements,” are in fact common to most primates. I should confess that this hadn’t occurred to me before, though I have watched baboons delicately picking berries from trees and vervet monkeys gleefully squeezing toothpaste, my toothpaste, out of its tube. Such is the power of our preconceptions.
Primates, of course, need opposable thumbs for their arboreal way of life and particularly for negotiating the thinner branches on the periphery of trees, where the ripe berries tend to be. But the discussion really becomes interesting when Mr. Wilkinson adds in the origin of the primate gait. Most other mammals walk with “a lateral sequence gait”: right hind leg, then right fore, then left hind, followed by left fore.
On the ground, this is “a wonderfully stable sequence” that maintains “a large triangular polygon of support.” But it wouldn’t work on the narrow branches of a tree. So primates instead use a “diagonal sequence gait,” right hind foot followed by left fore foot. This has the advantage of shifting most of the weight to the hind legs. And if the foreleg reaching out senses that the branch is too thin to support the animal’s weight, it’s also easier to tilt back and avoid a fall.
The diagonal gait’s rearward weight shift made the eventual move to an upright stance much easier and, combined with opposable thumbs, freed primate forelimbs “to become uniquely specialized for manipulation and food acquisition.” Manipulative forelimbs in turn made social grooming easier, Mr. Wilkinson writes. Grooming facilitated the more complex social lives that are characteristic of many primate species, and complex social lives led in turn to the development of larger brains. All this because some tree shrew-like creature among our distant ancestors “ventured boldly where no mammal had gone before: onto the flimsiest branches of the Late Cretaceous trees.”
With the help of his locomotory worldview, Mr. Wilkinson goes on to provide a similarly enlightening perspective on such major evolutionary developments as the transition from wriggling spineless marine organisms to the first vertebrates, the movement of fish out of the water and onto dry land, and the evolution of flight.
He has enough grasp of the average reader’s frame of mind to lighten his science at times. Among many other curious tidbits, we learn, for instance, that the odd walking style that female fashion models affect on the catwalk—one hip swinging a little too low on each stride, counterbalanced by the exaggerated sideways swaying of the torso—is known as a Trendelenburg gait, otherwise employed mainly by race walkers and chimpanzees. And to introduce us to the “central pattern generators” in our nervous system, which enable us to get where we want to go without having to think about every muscle movement, he recounts the incredibly complicated choices made, largely unconsciously, on a bicycle ride around Cambridge.
Unfortunately, Mr. Wilkinson often seems to be in too much of a hurry himself and neglects to slow down enough to bring the reader along with him. This is particularly a problem because the physics or genetics of any given form of locomotion can be extraordinarily complicated and deserve close explanation. But Mr. Wilkinson’s idea of being lucid, in describing the function of the Hox genes in embryo development, reads like this: “Simply put, their job is to translate the fore-to-aft morphogen gradients into a transcription factor expression pattern.”
Mr. Wilkinson may well be right that our four-billion-year history of locomotion “has given us everything we hold dear, down to the very awareness and curiosity that’s enabled us to piece that history together,” but it hasn’t given him the ability to tell that story properly. Long before he arrives at his conclusion, most readers will have used their powers of locomotion, regrettably, to put this book down and go elsewhere.