The most obvious examples of evolutionary biology's importance to medical understanding are related to infectious disease. As Jon Laman pointed out at the meeting, the immune system provides the perfect platform to explain the medical relevance of the exquisite evolutionary relationships between pathogens and their hosts. Understanding how virulence evolves, for example, can help predict the potential, sometimes counterintuitive (and controversial) negative consequences of imperfect vaccination. But evolution can also tell us that the origin of HIV was precipitated by a jump across the primate species barrier and enables us to predict the imminent arrival of avian flu and the mutations most likely to be responsible for that evolutionary leap from birds to humans. Where epidemiological and population genetic processes occur on the same time scale, the emerging field of “phylodyamics” can also inform us about the timing and progression of pathogen adaptation more generally. The relevance of evolution to medicine is, however, much broader. Participants at the York meeting discussed not only how vulnerability to cancer is an inevitable but unfortunate consequence of imperfect human engineering and natural selection (Mel Greaves, Institute of Cancer Research, UK), but how life history theory can potentially explain patterns of pregnancy loss (Virginia Vitzthum, Indiana University), how a comparative approach applied to different human cultures and different primates can improve rates of breastfeeding (Helen Ball, University of Durham), whether clinical depression has an adaptive origin (Lewis Wolpert, University College London), and if suicide attempts are really just evolutionary bargaining chips in intense social disputes (Ed Hagen, Humboldt University).
As with any emerging field, ideas change and the science is challenged. The thrifty gene concept —that some populations (e.g., from Polynesia) are particularly susceptible to type 2 diabetes and heart disease because of past selection pressure specifically during times of famine—no longer enjoys the support it once had. Tessa Pollard (University of Durham, UK) explained that the so-called Syndrome X is now considered to be the result of more general exposure to a rapid change in lifestyle as Western society encroached on these populations during the mid-20th century. The relationship between changing environment, diet, and susceptibility to disease, however, is also far from clear. Many diet-related conditions that typify industrialized populations—e.g., obesity, hypertension, and tooth decay—have been explained as resulting from an evolutionary mismatch between our over-refined, fat-filled contemporary diet and the environment to which humans were once ideally adapted. Sarah Elton (Hull York Medical School, UK) cautioned that while this analogy (the “environment of evolutionary adaptedness”) has been useful as a research tool and has led to public health campaigns for better diets (more seeds, nuts, fish oil, etc.), recreating such a typical “Stone Age diet” as a benchmark can be misleading. Human ecology in the past was at least as variable as human (and other primate) ecology is today.
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