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Evolutionary medicine or Darwinian medicine is the application of modern evolutionary theory to understanding health and disease. Modern biomedical research and practice have focused on the molecular and physiological mechanisms underlying health and disease, while evolutionary medicine focuses on the question of why evolution has shaped these mechanisms in ways that may leave us susceptible to disease. The evolutionary approach has driven important advances in the understanding of cancer, [1] autoimmune disease, [2] and anatomy. [3] Medical schools have been slower to integrate evolutionary approaches because of limitations on what can be added to existing medical curricula. [4] The International Society for Evolution, Medicine and Public Health coordinates efforts to develop the field. It owns the Oxford University Press journal Evolution, Medicine and Public Health and The Evolution and Medicine Review.
Utilizing the Delphi method, 56 experts from a variety of disciplines, including anthropology, medicine, nursing, and biology agreed upon 14 core principles intrinsic to the education and practice of evolutionary medicine. [5] These 14 principles can be further grouped into five general categories: question framing, evolution I and II (with II involving a higher level of complexity), evolutionary trade-offs, reasons for vulnerability, and culture. Additional information regarding these principles may be found in the table below.
Topic | Core Principle |
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Types of explanation (question framing) | Both proximate (mechanistic) and ultimate (evolutionary) explanations are needed to provide a full biological understanding of traits, including those that increase vulnerability to disease. |
Evolutionary processes (evolution I) | All evolutionary processes, including natural selection, genetic drift, mutation, migration and non-random mating, are important for understanding traits and disease. |
Reproductive success (evolution I) | Natural selection maximizes reproductive success, sometimes at the expense of health and longevity. |
Sexual selection (evolution I) | Sexual selection shapes traits that result in different health risks between sexes. |
Constraints (evolution I) | Several constraints inhibit the capacity of natural selection to shape traits that are hypothetically optimal for health. |
Trade-offs (evolutionary trade-offs) | Evolutionary changes in one trait that improve fitness can be linked to changes in other traits that decrease fitness. |
Life History Theory (evolutionary trade-offs) | Life history traits, such as age at first reproduction, reproductive lifespan and rate of senescence, are shaped by evolution, and have implications for health and disease. |
Levels of selection (evolution II) | Vulnerabilities to disease can result when selection has opposing effects at different levels (e.g. genetic elements, cells, organisms, kin and other levels). |
Phylogeny (evolution II) | Tracing phylogenetic relationships for species, populations, traits or pathogens can provide insights into health and disease. |
Coevolution (evolution II) | Coevolution among species can influence health and disease (e.g. evolutionary arms races and mutualistic relationships such as those seen in the microbiome). |
Plasticity (evolution II) | Environmental factors can shift developmental trajectories in ways that influence health and the plasticity of these trajectories can be the product of evolved adaptive mechanisms. |
Defenses (reasons for vulnerability) | Many signs and symptoms of disease (e.g. fever) are useful defenses, which can be pathological if dysregulated. |
Mismatch (reasons for vulnerability) | Disease risks can be altered for organisms living in environments that differ from those in which their ancestors evolved. |
Cultural practices (culture) | Cultural practices can influence the evolution of humans and other species (including pathogens), in ways that can affect health and disease (e.g. anti-biotic use, birth practices, diet, etc.). |
Adaptation works within constraints, makes compromises and trade-offs, and occurs in the context of different forms of competition. [6]
Adaptations can only occur if they are evolvable. Some adaptations which would prevent ill health are therefore not possible.
Other constraints occur as the byproduct of adaptive innovations.
One constraint upon selection is that different adaptations can conflict, which requires a compromise between them to ensure an optimal cost-benefit tradeoff.
Different forms of competition exist and these can shape the processes of genetic change.
Humans evolved to live as simple hunter-gatherers in small tribal bands, while contemporary humans have a more complex life. [13] [14] This change may make present-day humans susceptible to lifestyle diseases.
In contrast to the diet of early hunter-gatherers, the modern Western diet often contains high quantities of fat, salt, and simple carbohydrates, such as refined sugars and flours. [15] [16] [17]
Among different countries, the incidence of colon cancer varies widely, and the extent of exposure to a Western pattern diet may be a factor in cancer incidence. [18]
Examples of aging-associated diseases are atherosclerosis and cardiovascular disease, cancer, arthritis, cataracts, osteoporosis, type 2 diabetes, hypertension and Alzheimer's disease. The incidence of all of these diseases increases rapidly with aging (increases exponentially with age, in the case of cancer).
Of the roughly 150,000 people who die each day across the globe, about two thirds—100,000 per day—die of age-related causes. [19] In industrialized nations, the proportion is much higher, reaching 90%. [19]
Many contemporary humans engage in little physical exercise compared to the physically active lifestyles of ancestral hunter-gatherers. [20] [21] [22] [23] [24] Prolonged periods of inactivity may have only occurred in early humans following illness or injury, so a modern sedentary lifestyle may continuously cue the body to trigger life preserving metabolic and stress-related responses such as inflammation, and some theorize that this causes chronic diseases. [25]
Contemporary humans in developed countries are mostly free of parasites, particularly intestinal ones. This is largely due to frequent washing of clothing and the body, and improved sanitation. Although such hygiene can be very important when it comes to maintaining good health, it can be problematic for the proper development of the immune system. The hygiene hypothesis is that humans evolved to be dependent on certain microorganisms that help establish the immune system, and modern hygiene practices can prevent necessary exposure to these microorganisms. "Microorganisms and macroorganisms such as helminths from mud, animals, and feces play a critical role in driving immunoregulation" (Rook, 2012 [26] ). Essential microorganisms play a crucial role in building and training immune functions that fight off and repel some diseases, and protect against excessive inflammation, which has been implicated in several diseases. For instance, recent studies have found evidence supporting inflammation as a contributing factor in Alzheimer's Disease. [27]
This is a partial list: all links here go to a section describing or debating its evolutionary origin.
This section duplicates the scope of other articles, specifically Evolutionary psychology#Abnormal psychology.(February 2015) |
As noted in the table below, adaptationist hypotheses regarding the etiology of psychological disorders are often based on analogies with evolutionary perspectives on medicine and physiological dysfunctions (see in particular, Randy Nesse and George C. Williams' book Why We Get Sick). [43] Evolutionary psychiatrists and psychologists suggest that some mental disorders likely have multiple causes. [63]
Possible Causes of Psychological 'Abnormalities' from an Adaptationist Perspective Summary based on information in Buss (2011), [64] Gaulin & McBurney (2004), [65] Workman & Reader (2004) [66] | ||
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Possible cause | Physiological Dysfunction | Psychological Dysfunction |
Functioning adaptation (adaptive defense) | Fever / Vomiting (functional responses to infection or ingestion of toxins) | Mild depression or anxiety (functional responses to mild loss or stress) |
By-product of an adaptation(s) | Intestinal gas (byproduct of digestion of fiber) | Sexual fetishes (?) (possible byproduct of normal sexual arousal adaptations that have 'imprinted' on unusual objects or situations) |
Adaptations with multiple effects | Gene for malaria resistance, in homozygous form, causes sickle cell anemia | Adaptation(s) for high levels of creativity may also predispose schizophrenia or bi-polar disorder (adaptations with both positive and negative effects, perhaps dependent on alternate developmental trajectories) |
Malfunctioning adaptation | Allergies (over-reactive immunological responses) | Autism (possible malfunctioning of theory of mind module) |
Frequency-dependent morphs | The two sexes / Different blood and immune system types | Personality traits and personality disorders (may represent alternative behavioral strategies dependent on the frequency of the strategy in the population) |
Mismatch between ancestral & current environments | Modern diet-related Type 2 Diabetes | More frequent modern interaction with strangers (compared to family and close friends) may predispose greater incidence of depression & anxiety |
Tails of normal (bell shaped) curve | Very short or tall height | Tails of the distribution of personality traits (e.g., extremely introverted or extroverted) |
See several topic areas, and the associated references, below.
Charles Darwin did not discuss the implications of his work for medicine, though biologists quickly appreciated the germ theory of disease and its implications for understanding the evolution of pathogens, as well as an organism's need to defend against them.
Medicine, in turn, ignored evolution, and instead focused (as done in the hard sciences) upon proximate mechanical causes.
medicine has modelled itself after a mechanical physics, deriving from Galileo, Newton, and Descartes.... As a result of assuming this model, medicine is mechanistic, materialistic, reductionistic, linear-causal, and deterministic (capable of precise predictions) in its concepts. It seeks explanations for diseases, or their symptoms, signs, and cause in single, materialistic— i.e., anatomical or structural (e.g., in genes and their products)— changes within the body, wrought directly (linearly), for example, by infectious, toxic, or traumatic agents. [74] p. 510
George C. Williams was the first to apply evolutionary theory to health in the context of senescence. [32] Also in the 1950s, John Bowlby approached the problem of disturbed child development from an evolutionary perspective upon attachment.
An important theoretical development was Nikolaas Tinbergen's distinction made originally in ethology between evolutionary and proximate mechanisms. [75]
Randolph M. Nesse summarizes its relevance to medicine:
all biological traits need two kinds of explanation, both proximate and evolutionary. The proximate explanation for a disease describes what is wrong in the bodily mechanism of individuals affected by it. An evolutionary explanation is completely different. Instead of explaining why people are different, it explains why we are all the same in ways that leave us vulnerable to disease. Why do we all have wisdom teeth, an appendix, and cells that can divide out of control? [76]
The paper of Paul Ewald in 1980, "Evolutionary Biology and the Treatment of Signs and Symptoms of Infectious Disease", [77] and that of Williams and Nesse in 1991, "The Dawn of Darwinian Medicine" [78] were key developments. The latter paper "draw a favorable reception", [43] page x and led to a book, Why We Get Sick (published as Evolution and healing in the UK). In 2008, an online journal started: Evolution and Medicine Review.
In 2000, Paul Sherman hypothesised that morning sickness could be an adaptation that protects the developing fetus from foodborne illnesses, some of which can cause miscarriage or birth defects, such as listeriosis and toxoplasmosis. [79]
Arachnophobia is a specific phobia brought about by the irrational fear of spiders and other arachnids such as scorpions and ticks. The word Arachnophobia comes from the Greek words arachne and phobia.
The Paleolithic diet, Paleo diet, caveman diet, or Stone Age diet is a modern fad diet consisting of foods thought by its proponents to mirror those eaten by humans during the Paleolithic era.
Morning sickness, also called nausea and vomiting of pregnancy (NVP), is a symptom of pregnancy that involves nausea or vomiting. Despite the name, nausea or vomiting can occur at any time during the day. Typically the symptoms occur between the 4th and 16th week of pregnancy. About 10% of women still have symptoms after the 20th week of pregnancy. A severe form of the condition is known as hyperemesis gravidarum and results in weight loss.
Evolutionary biology is the subfield of biology that studies the evolutionary processes that produced the diversity of life on Earth. It is also defined as the study of the history of life forms on Earth. Evolution holds that all species are related and gradually change over generations. In a population, the genetic variations affect the phenotypes of an organism. These changes in the phenotypes will be an advantage to some organisms, which will then be passed on to their offspring. Some examples of evolution in species over many generations are the peppered moth and flightless birds. In the 1930s, the discipline of evolutionary biology emerged through what Julian Huxley called the modern synthesis of understanding, from previously unrelated fields of biological research, such as genetics and ecology, systematics, and paleontology.
George Christopher Williams was an American evolutionary biologist.
Ophidiophobia is fear of snakes. It is sometimes called by the more general term herpetophobia, fear of reptiles. The word comes from the Greek words "ophis" (ὄφις), snake, and "phobia" (φοβία) meaning fear.
Randolph Martin Nesse is an American physician, scientist and author who is notable for his role as a founder of the field of evolutionary medicine and evolutionary psychiatry.
Margaret J. "Margie" Profet is an American evolutionary biologist with no formal biology training who created a decade-long controversy when she published her findings on the role of Darwinian evolution in menstruation, allergies and morning sickness. She argued that these three processes had evolved to eliminate pathogens, carcinogens and other toxins from the body.
Paul Montgomery Bingham is an American molecular biologist and evolutionary biologist, Associate Professor in the Department of Biochemistry and Cell Biology at Stony Brook University and Vice President for Research at Rafael Pharmaceuticals. He is known for his work in molecular biology, and has also published recent articles and a book on human evolution.
Melvin Joel Konner is an American anthropologist who is the Samuel Candler Dobbs Professor of Anthropology and of Neuroscience and Behavioral Biology at Emory University. He studied at Brooklyn College, CUNY (1966), where he met Marjorie Shostak, whom he later married and with whom he had three children. He also has a PhD from Harvard University (1973) and a MD from Harvard Medical School (1985).
Evolutionary physiology is the study of the biological evolution of physiological structures and processes; that is, the manner in which the functional characteristics of individuals in a population of organisms have responded to natural selection across multiple generations during the history of the population. It is a sub-discipline of both physiology and evolutionary biology. Practitioners in the field come from a variety of backgrounds, including physiology, evolutionary biology, ecology, and genetics.
Evolutionary mismatch is the evolutionary biology concept that a previously advantageous trait may become maladaptive due to change in the environment, especially when change is rapid. It is said this can take place in humans as well as other animals.
Evolutionary approaches to depression are attempts by evolutionary psychologists to use the theory of evolution to shed light on the problem of mood disorders within the perspective of evolutionary psychiatry. Depression is generally thought of as dysfunction or a mental disorder, but its prevalence does not increase with age the way dementia and other organic dysfunction commonly does. Some researchers have surmised that the disorder may have evolutionary roots, in the same way that others suggest evolutionary contributions to schizophrenia, sickle cell anemia, psychopathy and other disorders. Psychology and psychiatry have not generally embraced evolutionary explanations for behaviors, and the proposed explanations for the evolution of depression remain controversial.
The Western pattern diet is a modern dietary pattern that is generally characterized by high intakes of pre-packaged foods, refined grains, red meat, processed meat, high-sugar drinks, candy and sweets, fried foods, industrially produced animal products, butter and other high-fat dairy products, eggs, potatoes, corn, and low intakes of fruits, vegetables, whole grains, pasture-raised animal products, fish, nuts, and seeds.
Loren Cordain is an American scientist who specializes in the fields of nutrition and exercise physiology. He is notable as an advocate of the Paleolithic diet.
Betsy Foxman is an American epidemiologist. She is the Hunein F. and Hilda Maassab Endowed Professor of Epidemiology and director of the Center for Molecular and Clinical Epidemiology of Infectious Diseases at the University of Michigan. She also served as Editor-in-Chief of the journal Interdisciplinary Perspectives on Infectious Diseases, is a member of the Infectious Disease Society of America and of the American College of Epidemiology.
Evolutionary psychiatry, also known as Darwinian psychiatry, is a theoretical approach to psychiatry that aims to explain psychiatric disorders in evolutionary terms. As a branch of the field of evolutionary medicine, it is distinct from the medical practice of psychiatry in its emphasis on providing scientific explanations rather than treatments for mental disorder. This often concerns questions of ultimate causation. For example, psychiatric genetics may discover genes associated with mental disorders, but evolutionary psychiatry asks why those genes persist in the population. Other core questions in evolutionary psychiatry are why heritable mental disorders are so common how to distinguish mental function and dysfunction, and whether certain forms of suffering conveyed an adaptive advantage. Disorders commonly considered are depression, anxiety, schizophrenia, autism, eating disorders, and others. Key explanatory concepts are of evolutionary mismatch and the fact that evolution is guided by reproductive success rather than health or wellbeing. Rather than providing an alternative account of the cause of mental disorder, evolutionary psychiatry seeks to integrate findings from traditional schools of psychology and psychiatry such as social psychology, behaviourism, biological psychiatry and psychoanalysis into a holistic account related to evolutionary biology. In this sense, it aims to meet the criteria of a Kuhnian paradigm shift.
The Extended Evolutionary Synthesis (EES) consists of a set of theoretical concepts argued to be more comprehensive than the earlier modern synthesis of evolutionary biology that took place between 1918 and 1942. The extended evolutionary synthesis was called for in the 1950s by C. H. Waddington, argued for on the basis of punctuated equilibrium by Stephen Jay Gould and Niles Eldredge in the 1980s, and was reconceptualized in 2007 by Massimo Pigliucci and Gerd B. Müller.
Social selection is a term used with varying meanings in biology.
Human evolutionary developmental biology or informally human evo-devo is the human-specific subset of evolutionary developmental biology. Evolutionary developmental biology is the study of the evolution of developmental processes across different organisms. It is utilized within multiple disciplines, primarily evolutionary biology and anthropology. Groundwork for the theory that "evolutionary modifications in primate development might have led to … modern humans" was laid by Geoffroy Saint-Hilaire, Ernst Haeckel, Louis Bolk, and Adolph Schultz. Evolutionary developmental biology is primarily concerned with the ways in which evolution affects development, and seeks to unravel the causes of evolutionary innovations.
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