I study how and why the human body is the way it is, especially the evolution of human physical activity. I am also interested in how that evolutionary history is relevant to preventing and treating diseases. To address these questions, I integrate three major lines of research: (1) experimental biomechanics and physiology in the lab, (2) fieldwork (mostly in Kenya and Mexico) to measure how people use their bodies in different cultures, and (3) analyses of the hominin fossil record in a comparative context.
Walking and Running
Bipedalism. When, how and why early hominins became bipeds? In collaboration with other researchers, I study early hominins such as Sahelanthropus and Australopithecus to understand how and why these hominins became bipeds, how they walked, ran and climbed, and how the evolution of human locomotion transformed the human body.
Running. When, how and why did humans become so exceptional as long distance endurance runners? My research with Dennis Bramble and other colleagues, suggests that long distance endurance running played a key role in the evolution of the genus Homo. We have found and continue to study novel human features, from head to toe, that help humans be superlative endurance runners, including spring-like arches in the foot, short toes, long tendons in the legs, a large gluteus maximus, unusually large joints in the legs and spine, a nuchal ligament connecting the head and neck, low and wide shoulders that are decoupled from the head, an elaboration of sweat glands, and loss of body fur.
Feet. How does the human foot work during walking and running without shoes? Humans have been walking and running for millions of years, and until recently we did so mostly barefoot or in very simple shoes such as sandals or moccasins. Our research shows that habitually barefoot or minimally shod humans tend to walk and run differently than shod people, often in a way that leads to very low collision forces, even on very hard surfaces. We are currently studying how barefoot styles of walking running may prevent common deformities and injuries.
Stability and economy. How do bipedal humans maintain stability and save energy when standing, walking and running? Since being bipedal is inherently less stable than being quadrupedal, hominins have had to evolve all sorts of mechanisms to save energy when standing (especially pregnant females), and to save energy and maintain stability of the center of gravity and the head when walking and even more so during running.
Many of the research questions I ask are motivated by an interest in using evolution to think not just why we get sick but also to find new, better ways to prevent and treat disease. The basis for this research (summarized in my 2013 book, The Story of Human Body: Evolution, Health and Disease) is that over the last few millions of years a series of transformations has adapted the human body to be slightly fat, furless, bipedal primates who crave sugar, salt, fat, and starch, but we are still adapted to eating a diverse diet of fibrous fruits and vegetables, nuts, seeds, tubers, and lean meat. In addition, although we are adapted to rest as much as possible, our bodies are still those of endurance athletes evolved to walk many miles a day, often run, as well as dig, climb, and carry. Although natural selection is still ongoing, recent cultural evolution is now a more powerful force, changing our bodies’ environments rapidly and profoundly. Many of these changes have been beneficial, but some have led to mismatches, which I define as conditions that are more common or severe because our bodies being inadequately or imperfectly adapted to novel environmental conditions. By treating the symptoms rather than the causes of these diseases we then stimulate a positive feedback loop which I term, dysevolution, that causes those diseases to remain prevalent or even become more severe.
Major mismatch diseases we study include: osteoarthritis, lower back pain, flat feet, and hypertensive heart disease.
Some of my research focuses on the unusual nature of the human head (for a summary, see my 2011 book: The Evolution of the Human Head, Harvard University Press). Unlike other mammals, we have very large brains, nearly balanced heads with short vertical necks that attach near the center of the skull’s base, no snouts, external noses, small teeth, short round tongues, a descended larynx, and tiny faces that are tucked almost beneath the frontal lobes. How, when, and why did these features evolve? What do they tell us about the selective forces that acted during human evolution? And how can we use an evolutionary approach to the head’s anatomy to prevent common problems such as malocclusions and myopia?