Lieberman studies the evolution of the human body, and he stresses the importance of considering future human evolution. Modern humans are “paradoxical” in that in some ways they are healthier than ever, and in some they are unhealthier. Malnutrition and infectious disease rates are lower and life expectancy is higher, but noncommunicable diseases are more prevalent. Many of these issues are caused by lifestyles, and they are straining economic and healthcare systems.

Discussions on health usually revolve around preventing or treating existing conditions, and few researchers consider human evolution as relevant. Lieberman argues that this is a mistake because evolution provides insight as to why humans are the way they are. Evolution is still taking place, particularly via culture.

Lieberman’s goal is to explore the health implications of biological and cultural evolution. He describes his explanations and methods as rigorous and fact-based, with in-text citations so that readers can easily fact-check the information. The discussion is limited, centering on a few relevant evolved traits and modern diseases, and Lieberman notes the information is subject to change as science progresses. He synopsizes his conclusion, declaring human evolution prioritizes reproduction over health. As a result, modern lifestyles create feedback loops that promote disease; however, this can be overcome with healthy diets and exercise.