The Story of the Human Body

The Story of the Human Body: Evolution, Health, and Disease (2013) is a science book by Daniel E. Lieberman. Lieberman is a paleoanthropologist, and he works as a researcher, author, and professor of Biological Sciences and of Human Evolutionary Biology at Harvard University. In The Story of the Human Body, Lieberman applies an evolutionary perspective to modern health concerns, centering on mismatch diseases, or diseases that arise from a mismatch between humans’ biological evolution and their environment. He argues that cultural evolution has outpaced biological evolution, which has contributed to the prevalence of mismatch diseases. Since cultural evolution has caused mismatch diseases, and since many mismatch diseases are preventable, then humans can improve their health and avoid mismatch issues by altering their cultural environments.

This guide uses the e-book version of The Story of the Human Body published by Pantheon Books in 2013.

Summary

Lieberman has focused his career on human evolution and its health implications. Through his studies, he has concluded that human evolution prioritizes reproduction rather than health. Modern lifestyles are misaligned with human evolution, leading to the prevalence of mismatch diseases, named for the mismatch hypothesis, which holds that some diseases arise from a mismatch between biological and environmental traits.

Biological evolution occurs through natural selection. Natural selection holds that individuals are genetically unique, that genetics are inherited from parents, and that individuals have unique reproductive rates which are impacted by the individual’s genetics. Natural selection can be negative, meaning it suppresses reproductive success, or positive. Positive natural selection increases reproductive rates, and the beneficial features are called adaptations. Whether a trait is adaptive is dependent on the environmental context. Five key evolutionary transitions that differentiated humans from apes include bipedalism, diverse diets, larger brains and bodies, slower physical development, and social skills. Humans are also impacted by cultural evolution, which is faster and more intentional than biological evolution. Two of the most important periods of cultural evolution are the Agricultural and Industrial Revolutions.

The first relevant stage of human evolution was the emergence of bipedalism. Researchers know that humans diverged from other apes millions of years ago, but they have yet to find the “missing link,” or the last common ancestor (LCA). They have, however, discovered some fossilized remnants of four early hominin species: Sahelanthropus tchadensis, Orrorin tugenesis, Ardipithecus kadabba, and Ardipithecus ramidus, with the last two species represented by the term “Ardi.” The fossils suggest these species were at least partially bipedal. Natural selection favored bipedalism during a global climate change occurring 5 to 10 million years ago. Bipedalism may have improved hominin species’ foraging abilities by helping them reach and carry food and conserve energy.

Next, Lieberman explores the dietary changes that took place within several Australopithecus species. These species, divided into the larger robust and smaller gracile species, lived between 4 and 1 million years ago in Africa. Their physical features—including their larger faces and teeth—suggest they had more diverse diets, including underground storage organs (USOs) like tubers, which are harder to chew. They also showed signs of advancing bipedalism. He connects their evolution to global climate change which turned rainforests into woodlands and grasslands, decreasing the availability of fruit.

The final hominin genus discussed is Homo. Early Homo species include H. habilis and H. erectus, which evolved larger brains, smaller snouts, and human-like physical and behavioral features. Experts speculate that H. erectus adopted hunter-gatherer lifestyles, which are defined by the gathering, hunting, processing, and sharing of foods. H. erectus groups became isolated and subject to unique natural selection, resulting in several hominin species, including humans, Neanderthals, and the Denisovans. Humans interbred with Neanderthals and Denisovans before outcompeting them and becoming the last remaining Homo species. Some traits that make humans unique are their large brains, their capacity for social and symbolic behaviors, their slow physical development, and their capacity for fat retention.

In Part 2, Lieberman dives deeper into the mismatch hypothesis. Mismatch diseases share a few predominant traits—they are noninfectious with obscured causes, they don’t interfere with reproduction, and their causes have cultural values. Lieberman illustrates this through the prevalence of dental cavities. Cavities are caused by bacteria that feed on starchy and sugary foods. Rather than eliminating such foods, humans use dental hygiene and procedures to mitigate cavities, which intensifies the prevalence of cavities. Lieberman calls such harmful evolutionary processes “dysevolution.”

Returning to his chronological discussion of human progression, Lieberman describes the emergence, benefits, and consequences of the Agricultural Revolution. Humans began farming shortly after the end of the Ice Age. Individual groups domesticated and ate different species, but with similar results. Agriculture provided more food to feed a growing population, but diets became less diverse and less healthy. Farmers often worked harder than hunter-gatherers, and they relied heavily on child labor. Social issues—social stratification, oppression, and war—followed the transition to agrarian lifestyles, as did mismatch diseases. Only around 300 generations have passed since the widespread implementation of agriculture, which is not enough time to result in significant evolutionary changes. Cultural evolution surpassed biological evolution, and this is the root cause of mismatch diseases.

A second major wave of cultural evolution that exacerbated mismatch diseases was the Industrial Revolution that began in the 1700s and which is characterized by fossil fuel use and scientific advancement. Industrialization radically changed daily life. In the beginning, environmental conditions worsened due to poor hygiene and medicine and a lack of labor laws, but gradually these facets of life improved. Diets changed, as people started relying on more high-calorie processed foods, and physical activity and sleep levels declined. Populations increased, as did life expectancies, resulting in a sharply inclining population, and people died more slowly from noncommunicable diseases. Some argue that higher morbidity is the price of modernity, but Lieberman disagrees and argues mismatch diseases are not inevitable.

In Part 3, Lieberman directly addresses several mismatch diseases. He divides them into three sections: Diseases caused by positive energy balances; inactivity or disuse; and novel cultural practices. Obesity-related diseases include type 2 diabetes, cardiovascular diseases, and reproductive cancers; diseases arising from disuse include osteoporosis and impacted wisdom teeth, and conditions caused by novel practices include foot and back pain and myopia, or nearsightedness. In each case, the diseases are sometimes preventable, and the common medical interventions fail to address the underlying causes, leading to the perpetuation of these diseases.

In the final chapter, Lieberman proposes four approaches to mitigating mismatch diseases: Natural selection, biomedical research, public health measures, and cultural change. He refutes the first three approaches, arguing they are relatively ineffective, and he strongly supports the fourth. If cultural evolution caused mismatch diseases, he argues, then humans can harness cultural evolution to prevent or reverse them.