Evolutionary medicine

From WikiMD
Jump to navigation Jump to search

Template:Evolutionary biology

The bacteria Mycobacterium tuberculosis can evolve to subvert the protection offered by immune defenses

Evolutionary medicine or Darwinian medicine is the application of modern evolutionary theory to understanding health and disease. The goal of evolutionary medicine is to understand why people get sick, not simply how they get sick. 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 antibiotic resistance,[1] cancer,[2] autoimmune disease,[3] and anatomy.[4] Medical schools have been slower to integrate evolutionary approaches because of limitations on what can be added to existing medical curricula.[5]

Key concepts

Important researchers in evolutionary medicine include: Randolph M. Nesse, George C. Williams, Paul W. Ewald, Stephen C. Stearns.

Trade-offs

A trade-off is a situation that involves losing one quality or aspect of something in return for gain of another. Trade-offs are pervasive in human physiology. The evolutionary perspective on trade-offs starts with the notion that changes in physiology that could reduce disease susceptibility might also lead to a decrease in fitness due to effects on other traits. This can be due to limited resources or simply to constraints on physiological capacities.

For instance, take the radial bone; the bone's shape and density has been shaped by natural selection for an optimal balance between strength, function, and cost of development and maintenance. It is relatively common for humans to break their distal radius from a fall. It is called a Colles' fracture. Evolutionary medicine helps us understand why people do not have a thicker bone that would be more resistant to this type of fracture. Humans' remarkable dexterity appears to come at a cost of increased risk of this type of fracture.

As another example, the capacity to repair and regenerate enables humans to respond to damage, but leave them susceptible to developing cancer. Inflammation is critical for response to injury. Chronic inflammation arises in settings of repeated damage. Chronic inflammation of the liver, also known as chronic hepatitis, is a major risk factor for hepatocellular carcinoma.[6]

Pathogens

The adaptive evolution of bacteria, viruses, other microbes and parasites plays a central role in medicine since this process is needed to understand antibiotic resistance,[7] pathogen virulence.[8] and pathogen subversion of the immune system.[9]

Antibiotic resistance

Microorganisms evolve resistance through natural selection acting upon random mutation. Once a gene conferring resistance arises to counteract an antibiotic, not only can those bacteria thrive, but that gene can spread to other types of bacteria through horizontal gene transfer of genetic information by plasmid exchange.

For more details on this topic, see antibiotic resistance

Virulence

The effect of organisms upon their host can vary from being symbiotic commensals that are beneficial, to pathogens that reduce fitness. Many pathogens produce virulence factors that directly cause disease, or manipulate their host to allow them to thrive and spread. Since a pathogen’s fitness is determined by its success in transmitting viable offspring to other hosts, it was thought at one time, that virulence moderated and it evolved toward commensality. However, this view is now questioned by Ewald.

For more details on this topic, see virulence, virulence factors and optimal virulence

Immune evasion

The success of any pathogen depends upon its ability to evade host immunity. Therefore, pathogens evolve methods that enable them to infect a host, and then evade detection and destruction by its immune system. These include hiding within host cells, within a protective capsule (as with M. tuberculosis), secreting compounds that misdirect the host's immune response, binding its antibodies, rapidly changing surface markers, or masking them with the host’s own molecules.

For more details on this topic, see manipulation of the immune system by pathogens, and evasion of the innate immune system

Defenses

Fever, pain, nausea, vomiting, diarrhea, cough, and anxiety are among the most common reasons why people seek medical care. At the same time, all of these are also defenses against certain dangers. For instance, fever is a defense against infection, a cough can in certain cases prevent pneumonia. However, these defenses can cause morbidity by being excessive in degree and frequency.[10]

For example, anemia of chronic disease is a defense that arises in the context of chronic inflammation, e.g. an autoimmune disease or chronic infection. A peripheral blood smear appears very similar to iron deficiency anemia, because of limited supply of iron for the stem cells synthesizing new red blood cells. The body has plenty of iron, but it is being sequestered by hepcidin, which is an acute phase protein secreted by the liver. This is adaptive during an infection because iron is required for bacterial growth.[11] Restricting bacterial access to iron restricts growth and aids the body to clear the infection. It is imperative to not confuse this defense with a disease because critically ill patients have been harmed by blood transfusions.[12] An evolutionary perspective enables one to make this crucial distinction.

If the cost of not eliciting a defense response, i.e. a false negative, greatly outweighs the cost of a reaction to something that is actually non-threatening, i.e. a false alarm, then one would expect a low threshold for defense activation. This phenomenon has been described as the "smoke detector principle",[10] or "better safe than sorry".[13] People put up with false alarms from our smoke detectors because the cost of them failing in the face of a real fire is potentially very high, while the cost of a false alarm is minor.[10] By a similar analogy, the "fight or flight" response has been selected to enhance survival against life-threatening situations. Because the cost of not responding could mean death, the threshold for eliciting an adrenal response is set relatively low. Panic disorder is repeated inappropriate activation of the "fight or flight" response. The smoke-detector principle promotes understanding for why humans are susceptible to this sometimes debilitating condition.

Other important examples include:

Human adaptations

Adaptation works within constraints, makes compromises and tradeoffs, and occurs in the context of different forms of competition.[19]

Constraints

Adaptations can only occur if they are evolvable. Some adaptations which would prevent ill health are therefore not possible.

  • 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.

Other constraints occur as the byproduct of adaptive innovations.

Trade-offs and conflicts

One constraint upon selection is that different adaptations can conflict, which requires a compromise between them to ensure an optimal cost-benefit tradeoff.

Competition effects

Different forms of competition exist and these can shape the processes of genetic change.

“Diseases of civilization”

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.[29][30] This change makes present humans vulnerable to a number of health problems, termed “diseases of civilization” and “diseases of affluence”. Humans were designed to live off of the land, and take advantage of the resources that were readily available to them. They were designed 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[31])

Diet

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.[32][33][34]

Life expectancy

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).

Age-Specific SEER Incidence Rates, 2003-2007

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.[35] In industrialized nations, the proportion is much higher, reaching 90%.[35]

Exercise

Many contemporary humans engage in little physical exercise compared to the physically active lifestyles ancestral hunter-gatherers.[36][37][38][39][40] It has been proposed that since prolonged periods of inactivity would have only occurred in early humans following illness or injury that it provides a cue for the body to engage in life-preserving metabolic and stress related responses such as inflammation that are now the cause of many chronic diseases.[41]

Cleanliness

Contemporary humans - due to medical treatment, frequent washing of clothing and the body, and improved sanitation - are mostly free of parasites, particularly intestinal ones. This causes problems in the proper development of the immune system although hygiene can be very important when it comes to maintaining good health. The hygiene hypothesis says that many modern humans are not exposed to microorganisms that have evolved in establishing the immune system as they should be. “Microorganisms and macroorganisms such as helminths from mud, animals, and feces play a critical role in driving immunoregulation” (Rook, 2012[42]). They play a crucial role in building and training immune functions to fight off and repel some diseases, and protect against excessive inflammation which has been implicated in several diseases (such as recent evidence for Alzheimer's Disease).[43]

Specific explanations

This is a partial list: all links here go to a section describing or debating its evolutionary origin.

Life stage related

Template:Colbegin

Template:Colend

Other

Template:Colbegin

Template:Colend

Evolutionary psychiatry / Clinical evolutionary psychology

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).[81] Evolutionary psychiatrists and psychologists suggest that some mental disorders likely have multiple causes.[82]

Possible Causes of Psychological 'Abnormalities' from an Adaptationist Perspective

Summary based on information in Buss (2011),[83] Gaulin & McBurney (2004),[84] Workman & Reader (2004)[85]

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.

Template:Colbegin

Template:Colend

History

Charles Darwin

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.[93] p. 510

George C. Williams was the first to apply evolutionary theory to health in the context of senescence.[48] 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.[94]

Randolph 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?[95]

The paper of Paul Ewald in 1980, “Evolutionary Biology and the Treatment of Signs and Symptoms of Infectious Disease”,[96] and that of Williams and Nesse in 1991, “The Dawn of Darwinian Medicine”[97] were key developments. The latter paper “draw a favorable reception”,[10]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.

Current activity in the field

Evolutionary medicine as a field began in the early 1990s, but has grown dramatically in recent years. These developments include the creation of the online publication, The Evolution & Medicine Review, which has served as a clearinghouse for important information in the field, two peer-reviewed journals (Evolution, Medicine and Public Health and Journal of Evolutionary Medicine), the founding of two evolution and cancer centers (The Center for Evolution and Cancer at UCSF and The Darwinian Evolution of Cancer Consortium in Montpellier) and The Center for Infectious Disease Dynamics at Penn State. There is now a national working group on evolutionary medicine education at the NSF sponsored National Evolutionary Synthesis Center, Infusing Medical Education with Evolutionary Thinking. Evolutionary Medicine programs have been established at a growing number of Universities, including UCLA, Arizona State University and Durham University in the UK.

See also

References

Metabolic.jpg

Featured disease

Metabolic syndrome is a cluster of the most dangerous heart attack risk factors: diabetes and prediabetes, abdominal obesity, high triglycerides, low HDL cholesterol and high blood pressure.

Affects one in three adults

Affecting about 35 percent of all adults in the United States according to the CDC, metabolic syndrome contributes to weight gain, by causing a state of internal starvation called metabolic starvation. This in turn leads to increases hunger, sugar cravings and increased portions leading to overeating and weight gain.

Cause and effect misunderstood

Since we traditionally thought that the portion control (which in turn was attributed wrongly to poor will power)is the cause of weight gain, rather than the effect of this metabolic starvation, all our traditional ideas about cause and effect of obesity were not only wrong but lead to the “blame the victim” attitude when it comes to obesity.

Secret of weight gain revealed

Secret of weight gain, and metabolic syndrome revealed - it has been recently proven that metabolic syndrome, and the weight gain itself are caused by a process called insulin resistance. Check your metabolic syndrome risk using the free Metabolic syndrome meter. Watch this amazing Ted Med video that reveals the secret of weight loss - Stop blaming the victim for obesity


Further reading

Books
Online articles

External links


Health science - Medicine
Anesthesiology - Dermatology - Emergency Medicine - General practice - Intensive care medicine - Internal medicine - Neurology - Obstetrics & Gynecology - Pediatrics - Podiatry - Public Health & Occupational Medicine - Psychiatry - Radiology - Surgery
Branches of Internal medicine
Cardiology - Endocrinology - Gastroenterology - Hematology - Infectious diseases - Nephrology - Oncology - Pulmonology - Rheumatology
Branches of Surgery
General surgery - Cardiothoracic surgery - Neurosurgery - Ophthalmology - Orthopedic surgery - Otolaryngology (ENT) - Plastic surgery - Podiatric surgery - Urology - Vascular surgery
A-Z health topics | Popular health topics

A |  B |  C |  D |  E |  F |  G |  H |  I |  J |  K |  L |  M | N |  O |  P |  Q |  R |  S |  T |  U |  V |  W |  X |  Y |  Z

Glossary of medical terms | Dictionary of medicine | Drugs A-Z | Topics in Medicine | Dictionary of drugs

WikiMD Resources for Evolutionary medicine

Articles

Most recent articles

Most cited

Review articles

Articles on Evolutionary medicine in N Eng J Med, Lancet, BMJ

Media Evolutionary medicine

Powerpoint slides

Podcasts and MP3's

Videos

Evidence Based Medicine

Cochrane Collaboration

Clinical Trials

Ongoing Trials on Evolutionary medicine

Trial results on Evolutionary medicine

Clinical Trials on Evolutionary medicine at Google

Books and news

Books on Evolutionary medicine

Evolutionary medicine in the news

Commentary Evolutionary medicine

Blogs on Evolutionary medicine

Patient Resources / Community

Patient resources

Discussion groups

Patient Handouts

Other resources

Social Media

Reddit
Quora.png
Pins
Instagram
YouTube videos
Flickr
Bing.png

W8MD Weight Loss, Sleep & MedSpa

A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U |V | W | X | Y | Z



W8md2.jpg

World's largest food, health, weight loss, wellnesspedia and encyclopedia

If you are a medical professional or an expert in any field of medicine, please join us in building the world's largest weight loss and wellness encyclopedia created by experts in the field, not by the crowd. WikiMD is sponsored by W8MD weight loss, sleep and medical aesthetic centers


W8MD Weight Loss, Sleep & Medical Aesthetic Centers

Since its inception in 2011, W8MD’s insurance physician weight loss program has successfully helped thousands of patients succeed in not only losing weight but also keep it off with an ongoing maintenance plan.

FANTASTIC PROGRAM. TRULY A LIFE CHANGER. D.M. LOST 100 LBS^^

weight loss success stories

^^Individual results may vary.

Weight-loss.jpg

W8MD weight loss, sleep and medical spa blogs


Support our sponsors

W8MD weight loss, sleep and medspa centers sponsors WikiMD.

W8MD's Locations for losing weight, sleeping better and looking your best

Philadelphia

weight loss Philadelphia | Sleep center Philadelphia

King of Prussia

Lose weight King of Prussia | sleep doctor King of Prussia

New York

Weight loss NYC | Fast weight loss NYC | Lose weight NYC | Sleep apnea NYC

New Jersey

New Jersey Weight Loss, Sleep and Medical Spa Cherry Hill NJ

Other W8MD blogs

Lorcaserin weight loss | Qsymia weight loss | Phentermine weight loss | Weight loss blog | Free weight loss | Saxenda weight loss | Contrave weight loss

Portions of content adapted from Wikipedias article on Evolutionary medicine licensed under GNU FDL.

References

Metabolic.jpg

Featured disease

Metabolic syndrome is a cluster of the most dangerous heart attack risk factors: diabetes and prediabetes, abdominal obesity, high triglycerides, low HDL cholesterol and high blood pressure.

Affects one in three adults

Affecting about 35 percent of all adults in the United States according to the CDC, metabolic syndrome contributes to weight gain, by causing a state of internal starvation called metabolic starvation. This in turn leads to increases hunger, sugar cravings and increased portions leading to overeating and weight gain.

Cause and effect misunderstood

Since we traditionally thought that the portion control (which in turn was attributed wrongly to poor will power)is the cause of weight gain, rather than the effect of this metabolic starvation, all our traditional ideas about cause and effect of obesity were not only wrong but lead to the “blame the victim” attitude when it comes to obesity.

Secret of weight gain revealed

Secret of weight gain, and metabolic syndrome revealed - it has been recently proven that metabolic syndrome, and the weight gain itself are caused by a process called insulin resistance. Check your metabolic syndrome risk using the free Metabolic syndrome meter. Watch this amazing Ted Med video that reveals the secret of weight loss - Stop blaming the victim for obesity


  1. 10.0 10.1 10.2 10.3 10.4 Cite error: Invalid <ref> tag; name "Nesse" defined multiple times with different content
  2. "Social Evolution Exam 2". Quizlet. Retrieved 30 June 2013.
  3. 19.0 19.1
  4. Williams, G. C. (1991). The dawn of darwinian medicine.Europe PubMed Central, 66(1), 1-22. Template:DOI
  5. 35.0 35.1
  6. Attention: This template ({{cite pmid}}) is deprecated. To cite the publication identified by PMID 20498671, please use {{cite journal}} with |pmid=20498671 instead.
  7. http://www.microbemagazine.org/index.php? option=com_content&view=article&id=4700:a-darwinian-view-of-the-hygiene-or-old-friends- hypothesis&catid=950&Itemid=1301
  8. 45.0 45.1
  9. 46.0 46.1 Straub, R. H., del Rey, A., Besedovsky, H. O. (2007) "Emerging concepts for the pathogenesis of chronic disabling inflammatory diseases: neuroendocrine-immune interactions and evolutionary biology" In: Ader, R. (2007) "Psychoneuroimmunology", Volume 1, Academic Press, San Diego, pp.217-232
  10. 47.0 47.1
  11. 48.0 48.1 abstract
  12. Bogin , B. (1997) "Evolutionary hypotheses for human childhood". Yearbook of Physical Anthropology. 104: 63-89 abstract
  13. Template:Cite PMID
  14. Template:Cite PMID
  15. Attention: This template ({{cite doi}}) is deprecated. To cite the publication identified by doi:10.1007/s00439-008-0559-8, please use {{cite journal}} with |doi=10.1007/s00439-008-0559-8 instead.
  16. Nesse, R., & Williams, G. (1996) Why We Get Sick. NY: Vintage.
  17. Gaulin, Steven J. C. and Donald H. McBurney. Evolutionary psychology. Prentice Hall. 2003. ISBN 978-0-13-111529-3, Chapter 1, p 1-24.
  18. Buss, D.M. (2011). Evolutionary Psychology.
  19. Gaulin & McBurney (2004), Evolutionary Psychology
  20. Workman & Reader (2004), Evolutionary Psychology

Ad. Tired of being overweight? W8MD's insurance weight loss* program can HELP | Advertise on WikiMD

Other languages:
English

Disclaimer: The entire contents of WIKIMD.ORG are for informational purposes only and do not render medical advice or professional services. If you have a medical emergency, you should CALL 911 immediately! Given the nature of the wiki, the information provided may not be accurate and or incorrect. Use the information on this wiki at your own risk! See full Disclaimer. * Individual results may vary.