A final theoretical approach to medical anthropology, emerging from biological anthropology, is evolutionary medicine. Evolutionary medicine sits at the intersection of evolutionary biology and human health, using the framework of evolution and evolutionary theory to understand human health. Evolutionary medicine asks why human health evolved the way it did, how environments affect health, and how we continue to affect our health through a number of factors including migration, nutrition, and epigenetics. The story of human evolution is the story of gene flow and human migration. Each individual human carries specific gene combinations, and each human population carries with it a common set of genes. When people migrate, they bring those genes with them. If they have children, they pass those genes on in new combinations. Culture impacts population genetics in two ways: migration patterns and culturally defined rules of sexual selection impact the frequency of gene alleles, and thus genetic variation, in a human population. These genes often affect health outcomes, such as the likelihood of developing certain types of cancer or immunity to specific pathogens through exposure. The more frequently a human population interacts with other populations through migration, trade, and other forms of cultural exchange, the more likely it is that genetic material from one population will be introduced to the other. The current level of globalization makes it possible for genes to flow from one corner of the globe to another. Moving into a new culture, whether forced or voluntary, requires adaptation. Adapting one’s culture to new rules, new norms, and new expectations, as well as adapting one’s identity to being a minority or facing oppression or prejudice, can affect the health of the migration population. An obvious example of this is the effects of slavery on Africans brought to the Americas. This impact is shown not just on their genetics, discussed elsewhere in this chapter, but also in their cultures. Syncretized religions like Haitian Vodou, Candomblé, and other African-inspired religions show the ways in which African populations adapted their beliefs to survive contact with oppression and cruelty, evolving and sanitizing certain elements while embracing others. Populations that are physically isolated for long periods of time might experience negative effects from genetic drift as the frequency of rare alleles increases over time. Similarly, cultural groups that practice strict endogamy can experience negative effects from genetic drift. In isolation, populations can sometimes see a rise in the frequency of maladaptive gene variants, as in the case of Tay-Sachs disease found in ethnic minority populations that practice endogamy, such as Ashkenazi Jews or French Canadians. Among these populations, which have been relatively isolated from the populations around them, the genes that cause Tay-Sachs have become more common than in other populations. This suggests that isolation and segregation can result in unhealthy changes in a population’s gene pool. Another example of evolutionary medicine is the study of the effects of the development of agriculture and the growth of urbanization on human health. The development of agriculture caused human health to change in many ways. Food became more regularly available, but diet became less varied and the amount of work required to procure the food increased. The regular movement associated with a gathering and hunting lifestyle resulted in robust overall fitness, but people were also at a greater danger of succumbing to a fatal accident before reaching the age at which they successfully reproduced. Our current lifestyle, in which many sit behind a desk for eight hours a day, five days a week, damages our spines and overall health. While food availability in Western nations is second to none, people living in those societies struggle with health problems related to being overweight and underactive. Each lifestyle has its trade-offs, and evolution has, over the past ten thousand years, affected both modern and neolithic humans differently. Through evolutionary health, we can track these changes and their adaptations. With human migration and the concentration of human populations in urban areas, disease has grown exponentially. Pathogens can now spread like wildfire across the world. In the past, disease has had a devastating effect on human populations. As just one example, the Black Death killed over a third of Europe’s population, spreading via Silk Road merchants and the conquests of the Mongol Empire. Today we see yearly flare-ups of influenza and Ebola and are still dealing with the devastating effects of the COVID-19 pandemic that caused nations to close borders and people within nations to limit social contact with one another. Globalization not only makes it possible for pathogens and pandemics to spread, but also allows nations to cooperatively distribute vaccines and coordinate methods to contain viruses. Nations can now share medical data to help develop treatments and help one another in efforts to isolate and quarantine the sick and infected. On the other hand, international cooperation can hamper local response and prevent cities, provinces, states, and nations from acting in their own best interest. Figure 17.12 World Health Organization (WHO) workers gear up to enter an Ebola ward in Lagos during the 2013–2016 Ebola pandemic. (Credit: Bryan Christensen/CDC Global/Wikimedia Commons, CC BY 2.0) At the heart of each of these areas of study is epigenetics, or the change of the expression of a gene during a single human lifetime. Often prompted by environmental exposure and mutations over a lifetime, epigenetic shifts are heritable changes in a person’s DNA that are phenotypical, meaning that they are linked to outwardly expressed traits. For example, studies show that people exposed to smoking in childhood tend to be shorter in adulthood. Similarly, trauma can stunt growth or increase the likelihood of developing specific maladaptations. The development of sickle cell anemia in the African American community has been linked to epigenetic adaptation to slavery in the United States, according to a 2016 study by Juliana Lindenau et al. This and other studies suggest that trauma can be inherited and can last generations. Epigenetics show evolution at work in real time, affecting both individuals and future generations.