In “The Story of the Human Body,” Daniel E. Lieberman, chairman of the Harvard Department of Human Evolutionary Biology, discusses the impact of natural selection and the dynamics of evolution over all those millennia on the bodies we inhabit. His argument is that many of the health problems we battle have arisen out of a kind of evolutionary mismatch, with our bodies
shaped by selective pressures that no longer govern whether we live or die — or reproduce. “Like it or not, we are slightly fat, furless, bipedal primates who crave sugar, salt, fat, and starch,” he writes, “but we are still adapted to eating a diverse diet of fibrous fruits and vegetables, nuts, seeds, tubers, and lean meat.
We enjoy rest and relaxation, but our bodies are still those of endurance athletes evolved to walk many miles a day, often run, as well as dig, climb, and carry.” We evolved to run barefoot, he argues; we evolved to squat, not to sit in chairs.
The first half of the book discusses human evolution, teasing out current evolutionary thought on such issues as our bipedal stance, our large brains, our dietary habits and our ability to store excess energy in the form of fat. The excitement of reasoning from evolutionary biology involves paying careful attention to structure and anatomy, physiology and function. Lieberman’s discussion of humans’ upright stance and its consequences — for everything from running and hunting to reproduction and spinal vulnerabilities — integrates structure and function, describing the kinds of tradeoffs and constraints that arise with evolutionary pressure and anatomic change.
To understand our evolutionary diet, you have to look at jaws and teeth, but also at energy metabolism and the different kinds of body fat. And of course, from an evolutionary perspective, it all comes back to reproductive success — that is, to the likelihood of creating genetic progeny. Lieberman is particularly good at drawing the connections between the different body systems: “Altogether, without lots of fat, human brains could not be so big, hunter-gatherer mothers would be less able to provide enough high-quality milk to nourish their big-brained offspring, and we would have less endurance.”
The discussion of human evolution takes Lieberman to the case he wants to make about our bodies in the modern world. And so, after discussing hunter-gatherers and the advent of agriculture, he takes us to the Industrial Revolution and a world that we have engineered to be substantially different from the one that engineered our bodies. The result of this mismatch — or these mismatches — is the increasing incidence of the diseases of plenty, comfort and civilization, from obesity and Type 2 diabetes to myopia, foot troubles and lower-back pain.
And Lieberman confronts the incredibly complex (and still, to coin a phrase, evolving) science around these diseases. This is not a book of simple arguments; to untangle the obesity problem, Lieberman invokes energy balance, sugar metabolism, hormones, sleep patterns, environmental change and long-standing debates over the evolutionary importance of body fat. I wish he had spent a little time on the issues that affect the elderly and on the consequences of extended life expectancy; the years after reproduction are often lost from evolutionary thinking, but the interplay of biology and aging is clearly important in understanding our 21st-century society — and probably our evolutionary history as well.
So what are the solutions? Lieberman is a barefoot runner and a strong advocate of barefoot running, but he does not present himself as an evolutionary ascetic; he’s not saying we should give up all the seductive comforts of warm houses (not to mention warm food) and the pleasures of soft chairs and chilled champagne. But he says that careful attention to the selective pressures that shaped our anatomy and physiology can help us protect ourselves against the dangers and discomforts that lurk paradoxically in a world designed — by us — to be safer and more comfortable.
Practically, this means acknowledging that it’s hard to change behavior just by telling people what is good for them — or even educating them more extensively about the dangers that lurk in luxury and comfort. Lieberman is arguing for more attention to prevention; we have evolved as big-brained, clever, tool-using problem-solvers, and our tendency, he says, is to find clever fixes for the symptoms of these new diseases, rather than to do the harder work of prevention. He argues for some modifications in child-rearing (more time barefoot, for the sake of their feet, more time outside, for the sake of their vision), and for environmental reengineering and “nudges” for adults, such as making stairs more accessible than elevators; and he makes an evolutionary case that “we sometimes need help from external forces in order to help ourselves.”
When I was an undergraduate, I thought evolution was the most interesting topic in the world, the place where scientific cleverness meets natural beauty and variety and the infinite quirkiness of biology. Lieberman evokes that excitement: the infinite interplay of form and function, structure and potential, and the constant intellectual challenge of weighing all the factors and trying to construct convincing evolutionary stories. Anatomic structure and physiological function impose all kinds of constraints on living organisms; the challenge of evolutionary biology is often to avoid the pitfalls of teleology (we stood upright to conquer the Earth) and to understand the forces that shaped structure and were selected for function, and the tradeoffs that emerged.
These are not debates to gloss over or reduce to simple statements of cause and effect — they are stories with scientific complexity and tremendous, sometimes contradictory accumulations of evidence and detail. “The Story of the Human Body” does full justice to those stories, to that evidence and to that detail, and brings them to bear on daily health and well-being, individual and collective.
is a professor of journalism and pediatrics and the director of the Arthur L. Carter Journalism Institute at New York University.