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Evolutionary medicine


Evolutionary medicine or Darwinian medicine is the application of modern evolutionary theory to understanding health and disease. Modern medical research and practice has 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 our understanding of cancer,autoimmune disease, and anatomy. Medical schools have been slower to integrate evolutionary approaches because of limitations on what can be added to existing medical curricula.

Adaptation works within constraints, makes compromises and tradeoffs, and occurs in the context of different forms of competition.

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, a very different way of life and environment compared to that faced by contemporary humans. This change makes present humans vulnerable to a number of health problems, termed "diseases of civilization" and "diseases of affluence". Humans evolved to live off of the land, and take advantage of the resources that were readily available to them. They evolved for the stone-age, and the environments of today bring about many disease causing ailments, that may or may not be deadly. "Modern environments may cause many diseases-for example, deficiency syndromes such as scurvy and rickets" (Williams, 1991)

In contrast to the diet of early hunter-gatherers, the modern Western diet often contains high quantities of fat, salt, and simple carbohydrates, which include refined sugars and flours. These create health problems.

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).


Possible Causes of Psychological 'Abnormalities' from an Adaptationist Perspective

Summary based on information in Buss (2011), Gaulin & McBurney (2004), Workman & Reader (2004)

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)

  • DNA cannot be totally prevented from undergoing somatic replication corruption; this has meant that cancer, which is caused by somatic mutations, has not (so far) been completely eliminated by natural selection.
  • Humans cannot biosynthesize vitamin C, and so risk scurvy, vitamin C deficiency disease, if dietary intake of the vitamin is insufficient.
  • Retinal neurons and their axon output have evolved to be inside the layer of retinal pigment cells. This creates a constraint on the evolution of the visual system such that the optic nerve is forced to exit the retina through a point called the optic disc. This in turn creates a blind spot. More importantly, it makes vision vulnerable to increased pressure within the eye (glaucoma) since this cups and damages the optic nerve at this point, resulting in impaired vision.
  • Williams, George; Nesse, Randolph M. (1996). Why We Get Sick: the new science of Darwinian medicine. New York: Vintage Books. ISBN . 
  • Stearns SC, Koella JK (2008). Evolution in health and disease (2nd ed.). Oxford [Oxfordshire]: Oxford University Press. ISBN . 
  • McKenna, James J.; Trevathan, Wenda; Smith, Euclid O. (2008). Evolutionary medicine and health: new perspectives (2nd ed.). Oxford [Oxfordshire]: Oxford University Press. ISBN . 
  • O'Higgins, Paul; Sarah Elton (2008). Medicine and Evolution: Current Applications, Future Prospects (Society for the Study of Human Biology Symposium Series (Sshb). Boca Raton: CRC. ISBN . 
  • Ewald, P. W. (1996). Evolution of Infectious Disease. Oxford: Oxford University Press. ISBN . 
  • Moalem, S.; Prince, J. (2007). Survival of the Sickest. New York: HarperLuxe. ISBN . 
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