Professor of Human Evolutionary Biology, Harvard University
Why does the human body look the way it does?
I think this is an important question to tackle from an evolutionary perspective not only to understand better why humans are the way they are, but also because the evolutionary bases of human anatomy and physiology provide insights on how to prevent many kinds of illnesses and injuries.
Much of my research focuses on the unusual nature of the human head. 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? And what do they tell us about the selective forces that acted during human evolution?
The human body below the neck is also unusual in several respects related to locomotion. I am especially interested in four questions:
1. When, how and why early hominins became bipeds? Work on Sahelanthropus in collaboration with Michel Brunet suggests that this earliest hominin was a biped and that the origins of bipedal walking was a major factor that helped set humans on a novel evolutionary trajectory from the African apes.
2. 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 us be great 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.
3. How does the human foot work during running with and without shoes? Humans have been running for millions of years, and until recently it was mostly barefoot or in very simple shoes (sandals or moccasins). Our research shows that habilitually barefoot or minimally shod humans tend not to land on their heels, and instead strike the ground in a way that leads to very low collision forces, even on very hard surfaces. This style of running may have other benefits, which we are currently studying as well.
4. How do bipedal humans maintain stability 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.
My lab employs a host of experimental and comparative methods to examine how key human features grow and develop, how they function, how their function affects performance, and how and when they evolved. Major methods used in my lab include: