LAUSR

We live in an extraordinary time where many of our behavioral, morphological, physiological traits and developmental pathways—honed by many generations of natural selection—are suddenly no longer beneficial. Indeed, these adaptations may be deleterious in our current, highly industrialized and human-modified environments. A foundational insight from evolutionary medicine is that “modern epidemics are most likely to arise from the mismatch between physiological design of our bodies and novel aspects of our environment” (Nesse and Williams 1998: 93). In the present article, we suggest that. although there have been vast increases for humanity in the usual metrics of health since hunter–gatherer days in the form of, for example, longer life expectancy and lower child mortality, not all trends are in the same direction. Mismatches are hiding in plain sight, creating epidemics that cause immense human suffering and expense; a more holistic functional perspective can help us identify them and, in doing so, improve individual and public health. Scientists interested in evolutionary medicine have examined the problems related to bringing hunter–gatherer genomes into a McDonald’s environment. Initial efforts, quite naturally, were focused on changes in the chemical constitutions of human diets (Leonard 2008). But the environmental changes we have made go far beyond the agricultural revolution to urbanization, subsequent industrialization, and the widespread creation of novel chemicals and pollutants. Together, these changes not only have decimated Earth’s biota but have entrained a multidimensional human health epidemic whose causes and serious consequences have yet to be properly recognized, because to recognize it, we must adopt a broad, integrative view. Such a holistic approach contrasts with the culture of extreme specialization that has led to some of our recent biomedical advances. Without stepping back and asking questions about the historical function of traits, we fear that, in future, some such advances will be stifled. Consider the jaw. Jaws have been largely isolated from physicians’ concerns with the rest of the body and are thought to be the preserve of an entirely different type of caregiver—dentists, who have their own schools, traditions, and techniques. The hunter–gatherer– industrial mismatch in the nutritional content in food have been thoroughly studied by medical scientists and brought to the public’s attention in endless debates and books about sugars, fats, gluten, obesity, diabetes, Paleo diets, and on and on. But nary a word about the mismatch of jaws with the consistency or “chewability” of foods (e.g., Nesse et al. 2010, Stearns 2012, Grunspan et al. 2018). We’re urged to exercise virtually every skeletal muscle in our body—use it or lose it—except our jaw muscles and tongues. A lack of exercise of our jaw muscles, a result of diminished nursing and weaning to a softer, more liquid diet, has contributed to a shrinkage of human jaws (Lieberman et al. 2004, Lieberman 2013) and the resultant plague of malocclusion (crooked teeth) and braces (Kahn and Ehrlich 2018). The difference in chewing environment is only one factor in this now welldocumented trend of declining jaw size, primarily in developed countries (e.g., Mohlin et al. 1978). Another is moving indoors, where allergens are concentrated, leading to children (especially those in communal child care) to have stuffy noses, which, in turn, result in mouth-breathing and poor oral posture (Kahn and Wong 2016), which disrupts proper jaw development (Harvold et al. 1981) and often generates a narrowed airway and sleep apnea (Harari et al. 2010). The latter, frequently exacerbated by orthodontic cosmetic treatment, is the most serious aspect of the jaws epidemic and is increasingly treated with CPAP machines. Sleep deprivation is an important chronic stressor (Sapolsky 2004), and being regularly awakened in the middle of the night choking (as happens with sleep apnea) presumably also is. Stress makes us much more susceptible to disease, although details of degree and mechanisms remain debatable (Cohen et al. 2007). As was stated in one review, “Stress is a critical crosscutting process that . . . represents modifiable variance in the etiology of disease, affects nearly every behavior that contributes to good or bad health outcomes, and has direct effects on all or most bodily systems and can thereby contribute to developing health problems as well” (Dougall and Baum 2011: 69). In 2012, for the first time, research showed that the effects of psychological stress on the body’s ability to regulate inflammation can promote the development and progression of disease (Cohen et al. 2012). Other mismatches are causing obvious health epidemics that, like the jaws epidemic, have not been given enough joint attention by evolutionary biologists and physicians, and at least one mismatch threatens life as we know it. It has been estimated that half the people in developed nations are sleep deprived, and the World Health Organization has declared a sleep loss epidemic (Walker 2017). We sleep in situations very different from the circumstances under which we evolved—artificial lighting is nearly ubiquitous—and, as was described above, sleep apnea interferes with quality sleep. Sleep loss contributes to health