Evolution and medicine.

Evolutionary medicine is a new field whose goal is to incorporate an evolutionary perspective into medical education, research, and practice. Evolutionary biologists and physicians have traditionally been concerned with different problems and have developed different ways of approaching and understanding biological phenomena. Evolutionary biologists analyze the properties of populations and the ways in which populations change over time, while physicians focus on the care of their individual patients. Evolutionists are concerned with the ultimate causes of biological phenomena, causes that operated during the phylogenetic history of a species, while physicians and biomedical scientists have been more interested in proximate causes, causes that operate during the ontogeny and life of an individual. Evolutionary medicine is based on the belief that an integration of these complementary views of biological phenomena will improve our understanding of health and disease. This essay reviews the theory of evolution by natural selection, as it was developed by Darwin and as it is now understood by evolutionary biologists. It emphasizes the importance of variation and selection, points out the differences between evolutionary fitness and health, and discusses some of the reasons why our evolutionary heritage has left us vulnerable to disease.

Evolution in health and medicine Sackler colloquium: Making evolutionary biology a basic science for medicine.

New applications of evolutionary biology in medicine are being discovered at an accelerating rate, but few physicians have sufficient educational background to use them fully. This article summarizes suggestions from several groups that have considered how evolutionary biology can be useful in medicine, what physicians should learn about it, and when and how they should learn it. Our general conclusion is that evolutionary biology is a crucial basic science for medicine. In addition to looking at established evolutionary methods and topics, such as population genetics and pathogen evolution, we highlight questions about why natural selection leaves bodies vulnerable to disease. Knowledge about evolution provides physicians with an integrative framework that links otherwise disparate bits of knowledge. It replaces the prevalent view of bodies as machines with a biological view of bodies shaped by evolutionary processes. Like other basic sciences, evolutionary biology needs to be taught both before and during medical school. Most introductory biology courses are insufficient to establish competency in evolutionary biology. Premedical students need evolution courses, possibly ones that emphasize medically relevant aspects. In medical school, evolutionary biology should be taught as one of the basic medical sciences. This will require a course that reviews basic principles and specific medical applications, followed by an integrated presentation of evolutionary aspects that apply to each disease and organ system. Evolutionary biology is not just another topic vying for inclusion in the curriculum; it is an essential foundation for a biological understanding of health and disease.

Evolutionary biology: a basic science for medicine in the 21st century.

Evolutionary biology was a poorly developed discipline at the time of the Flexner Report and was not included in Flexner's recommendations for premedical or medical education. Since that time, however, the value of an evolutionary approach to medicine has become increasingly recognized. There are several ways in which an evolutionary perspective can enrich medical education and improve medical practice. Evolutionary considerations rationalize our continued susceptibility or vulnerability to disease; they call attention to the idea that the signs and symptoms of disease may be adaptations that prevent or limit the severity of disease; they help us understand the ways in which our interventions may affect the evolution of microbial pathogens and of cancer cells; and they provide a framework for thinking about population variation and risk factors for disease. Evolutionary biology should become a foundational science for the medical education of the future.

Mouse models of human disease: An evolutionary perspective.

The use of mice as model organisms to study human biology is predicated on the genetic and physiological similarities between the species. Nonetheless, mice and humans have evolved in and become adapted to different environments and so, despite their phylogenetic relatedness, they have become very different organisms. Mice often respond to experimental interventions in ways that differ strikingly from humans. Mice are invaluable for studying biological processes that have been conserved during the evolution of the rodent and primate lineages and for investigating the developmental mechanisms by which the conserved mammalian genome gives rise to a variety of different species. Mice are less reliable as models of human disease, however, because the networks linking genes to disease are likely to differ between the two species. The use of mice in biomedical research needs to take account of the evolved differences as well as the similarities between mice and humans.

Life histories of pathogen populations.

The populations of pathogens in individual hosts have many of the characteristics of multicellular organisms, or individuals. These populations go through a life cycle within a host and they reproduce by founding daughter populations in new hosts. Natural selection shapes the life history characteristics of pathogen populations--life expectancy, trade-offs in the allocation of resources between growth, survival, and fecundity, and aging--in ways that maximize the reproductive fitness of the pathogens. In turn, these life history characteristics shape the natural histories of infectious diseases. Transmissibility and virulence may be thought of as properties of pathogen populations rather than as properties of the constituent microorganisms within these populations. The poor correlation of virulence with pathogen fitness is a major obstacle to the development of a theory of virulence. Consideration of the life histories of pathogen populations complements the traditional epidemiological focus on host populations and provides a valuable perspective for understanding human infectious diseases.

Why disease persists: an evolutionary nosology.

Although natural selection might be expected to reduce the incidence and severity of disease, disease persists. Natural selection leads to increases in the mean fitness of populations and so will reduce the frequency of disease-associated alleles, but other evolutionary processes, such as mutation and gene flow, may introduce or increase the frequency of these deleterious alleles. The pleiotropic actions of genes and the epistatic interactions between them complicate the relationship between genotype and phenotype, and may result in the preservation of disease-associated alleles. Deleterious alleles may also be maintained because of linkage to beneficial alleles. The inability of natural selection to eliminate diseases of aging is a reminder that fitness -- success in producing progeny, or in contributing genes to the population gene pool -- is not equivalent to the absence of disease. Nutritional or psychosocial cues may lead to life history strategies that maximize survival to reproductive maturity at the expense of disease later in life. Natural selection acts on genes, cells, and groups, as well as on organisms; the outcome of evolution reflects selection at different levels of biological organization. Finally, the human environment is constantly changing, largely because of the evolution of our parasites and because of changes in cultural beliefs and practices; genetic evolution is comparatively slow and lags behind environmental change. An evolutionary nosology complements traditional medical nosologies and enhances our understanding of the persistence of disease and the meaning of human variation.

Disparities and discrimination in health care: an introduction.

Racial disparities in health care and health outcomes are a disturbing feature of the American health care system. Efforts to reduce or ameliorate these disparities must be informed by an understanding of the factors that underlie and contribute to them. The papers in this issue are based on a recent conference that was held at the University of Chicago to address this problem. Socioeconomic status is an important determinant of health, and socioeconomic disparities are major determinants of the racial disparities in health. These socioeconomic disparities are complicated by access to health insurance, geographic factors, and unhealthy behaviors. Geographic disparities, both regional and local, also contribute to racial disparities in health. Moreover, current disparities in the health of adult populations may reflect socioeconomic disparities that prevailed during their intrauterine or early infant development. There seems little evidence that either overt or unconscious discrimination on the part of physicians is an important cause of racial disparities in health; blaming physicians for this problem is counterproductive. Improving the quality of medical care holds the promise not only of improving health for all Americans, but of decreasing the racial disparities in health care that are so troubling today.

Why is revitalizing clinical research so important, yet so difficult?

We believe that support for academic clinical research has greatly declined in recent decades. Here we discuss our views on why this has happened. We define clinical or patient-oriented research as limited to the study of human beings or populations of individuals, and argue that its eclipse in favor of basic and "translational" research is the result of inappropriate conceptual paradigms or "models" for medical advances. We believe that medical history shows that the "bench-to-bedside" model is inadequate to explain most recent progress and that clinical advances themselves often lead to new basic research. Discussion of alternate conceptual frameworks for biomedical research should help lead to changes in funding and organizational structures that might finally revitalize clinical research.