Reducing the genome to a single copy during meiosis

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Unformatted text preview: lly diverse offspring (12, 13). Reducing the genome to a single copy during meiosis seems wasteful; why not have oocytes that start with many cells? Meiosis and crossing-over may have evolved to help minimize the penetration of supersel sh genes that arrange for their own preferential transmission at the expense of other genes and an individual’s health (14) and to repair damaged DNA sequences. Why is cancer so persistent, and why does its prevalence increase at older ages? The evolutionary answer arises from the limits of selection in eliminating deleterious alleles, tradeoffs with the bene ts of tissue repair, and genetic changes induced by pathogens (15). Why do humans tend to have only one offspring at a time (16)? Why is rst reproduction delayed for ≈20 years? Such traits receive evolutionary analysis in life history theory (17, 18). Why do individuals often act in ways that decrease their own survival and reproduction? One reason is that such actions can increase the reproductive success of relatives who have identical genes (19, 20). Another is that investing in mate competition has relatively greater tness payoffs for males, thus explaining the 300% excess of male vs. female mortality rates at sexual maturity in modern populations (21). Yet another is that our dietary and exercise preferences were shaped in environments fundamentally different from those common now (22). What are the evolutionary reasons for capacities for pain, fever, and negative emotions? Although painful and costly, they are adaptive responses that evolved in conjunction with regulatory mechanisms that express them in situations where they are useful (23, 24). Nesse et al. Investigations into such questions have tested scores of evolutionary hypotheses, many with speci c applications in medicine (25–28). New Genetic Data and Methods New progress is also made possible by availability of vast amounts of genetic data and associated new methods for generating and analyzing DNA sequence and gene expression data. This is perhaps most obvious in our new ability to use genetic information to trace phylogenies of species, subpopulations, and genealogies of individuals (4). New data and methods also allow estimation of the strength of selection acting at a given locus, allowing us to test hypotheses about selection in humans (29, 30). For example, strong signals of selection surround the locus of the alcohol dehydrogenase gene in Southeast Asians (31). It is also now possible to test evolutionary theories about differences in selection acting on genes derived from paternal and maternal sources, as in the case of imprinted genes (32). Accurate measurements of mutation accumulation have also become a reality (33); this might enable us to address long-standing questions about the consequences of mutation accumulation or the load of mutations (34). We are only beginning to discover the many ways that genetic data can be used to generate and test evolutionary hypotheses and the ways that evolutionary theory can guide genetic studies and help to interpret unexpected results (35). Increasing distance from 19th-century theories of degeneration and 20th-century eugenics makes it easier to recognize the value of modern evolutionary applications in helping individual patients. In the late 19th century, Spencer’s ideas were more in uential than Darwin’s, with detrimental effects on evolutionary biology. In the early 20th century, evolutionary approaches to health emphasized eugenics, supposed racial superiority, and fears of degeneration, exploited by the Third Reich (36). When Nazi horrors were publicized at the end of World War II, scienti c publications on evolution and medicine ceased suddenly (37). Although associations linger from previous links to eugenics, repudiation of such social policies is now so widely shared that it is easier to recognize the ways that evolutionary biology can help us understand diseases. New evolutionary approaches to medicine are almost entirely unconnected with these earlier movements. Modern approaches tend to distance themselves actively from concerns about races and the species. Instead, they focus on ways that evolutionary biology can help to solve medical problems of individuals and meet the public health needs of communities (37). Finally, evolutionary approaches are growing in medicine thanks to new publications and broader education of physicians and researchers. Controversy about teaching evolution in public schools continues to inhibit evolution education, but it also has stimulated interest in many of the best students (38). Several recent books on evolutionary approaches to medicine (25, 27, 28, 39, 40) have given rise to many new undergraduate courses on the topic, and recent international conferences have brought together those working in related areas, with predictable synergy (26, 41, 42). Recommendations About Education Approaches for Evolution in Medicine Despite this progress, few physicians and medical researchers have had a formal course in evolutionary biology, and even fewer have had a chance to learn speci c applications in medicine and public heal...
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This document was uploaded on 01/31/2014.

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