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Chapter 12

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Psychology 3229A/B
Scott Mac Dougall- Shackleton

Chapter 12: Evolutionary Psychopathology and Darwinian Medicine WhatAre Evolutionary Psychopathology and Darwinian Medicine? • Psychopathology is the study of mental illness - so we can think of evolutionary psychopathology as the Darwinian approach to the study of mental illness • Darwinian medicine is also concerned with improving our understanding of mental illness by applying evolutionary principles but is somewhat broader since it also encompasses non- psychiatric health problems • Darwinian medicine differs from conventional medicine in the same way that evolutionary psychology differs from the traditional social sciences - that is, whereas conventional medicine deals with the proximate questions of ‘how’and ‘what’, Darwinian medicine is concerned with ultimate ‘why’questions • This means that evolutionists are interested more in why each health-related problem continues to exist today rather than in the mechanism of causation Infectious Diseases and The EvolutionaryArms Race • When we are ill with an infectious disease we are really saying that our body has become host to a pathogen which is causing us a number of unpleasant symptoms • Such pathogens include viruses, bacteria and other microbial parasites • Conventional medicine seeks to understand the etiology (cause) and the pathogenesis (mechanism) of each illness • From such a proximate level of understanding clinicians aim to develop treatments to help alleviate the symptoms and destroy the pathogen • Darwinian medicine, however, seeks ultimate explanations for the symptoms of disease in order to aid treatment • Asks why such symptoms exist - what function, is any, they might serve • Darwinian medicine is not attempting to replace conventional medicine but rather be used to provide an overarching framework for understanding health and illness • Evolutionary approach view the host parasite relationship as an arms race conducted on an evolutionary time scale where each side struggles to gain the upper hand • Evolutionists have suggested that many of our symptoms may well be defense mechanisms which have evolved to protect us • Bacterial Infections • Bacteria are single-celled microbial organisms • Bacterial infections lead the body to release a chemical called leucocyte endogenous mediator or LEM that leads to both a raising of the body temperature and to iron withdrawal from the bloodstream • However the doctor frequently prescribes antipyretic drugs and iron supplements which can help to maintain the illness • Viral Infections • Viruses are sub-microscopic • These pathogens may be sub-divided into DNAand RNAviruses Chapter 12: Evolutionary Psychopathology and Darwinian Medicine Fighting Back - The Immune System • The part of the immune system that is found in the blood consists of an army of specially adapted white cells or lymphocytes • There are two main categories of these cells: B-lymphocytes, which are formed in the bone marrow, and T-lymphocytes, which develop in the thymus at the base of the neck • The immune system is activated by the entry of large foreign molecules known as antigens into the body • When a pathogen is detected T-lymphocytes begin to proliferate and form various sub-classes that both help in the attack of the antigen and aid the B-lymphocytes in their production of antibodies • The body keeping a relatively small number of each specific white blood cell • When a lymphocyte comes across an antigen that fits the lock, it then begins to multiply, producing vast numbers of identical ones to fight the foreign body HIV andAIDS - The Virus That Cheats the System? • One virus which has cheated the system does not attempt to avoid the attentions of the immune system, nor does it cloak itself, it simply attacks the immune system itself • The human immunodeficiency virus or HIV binds to the surface of the helper T cells, gains entry and then destroys them • HIV andAIDS illustrate two important points with regard to host-parasite relationships • First they show how our own behaviour can alter the evolution of pathogens • Second, they illustrate that we cannot win the host-parasite arms race outright byt only gain a temporary respite with each bug • Ewald has proposed that the virulence of a pathogen is strongly influenced by its method of transmission • Those that are passed on directly by personal contact, he suggests, should be less debilitating than those that are passed on by a vector Psychiatric Problems • Darwinian medicine have already considered a wide range of mental health problems including depression and anxiety, schizophrenia and serious personality disorders Why Can’t Evolution Rid Us of Psychiatric Problems? • Nesse and Williams have suggested three ultimate reasons as to why many modern-day humans have psychiatric problems: • Genes that predispose people to psychiatric disorders may also have inclusive fitness benefits • Environmental factors that cause psychiatric disorders may be novel when compared to our ancestral past • Some psychiatric disorders may be due to design compromises rather than genetic flaws • We might label the first of these the pleiotropy argument - that is, many genes have more than one phenotypic effect, so the negative effects of a gene may be maintained in a gene pool because the positive ones outweigh them Chapter 12: Evolutionary Psychopathology and Darwinian Medicine • The second argument we could call the time lag argument - that is, humans have developed a lifestyle that did not exist in our ancestral past too rapidly for selection pressures to have led to appropriate changes • Finally, we might call the third one the compromise argument - that is, selection pressures act on inclusive fitness, not on perfecting psychological devices • The trait variation argument is based on the notion of a normal distribution curve • This means that within a given population, individuals may be plotted along various dimensions for physical traits and for psychological traits Anxiety - Why Worry? • When threatened, anxiety focuses our attention and prepares us for action in a way that would have been advantageous to our ancestors • The Smoke Detector Principle • Nesse and Williams suggest that in order to understand just why we worry so much we need to consider how the mechanisms that regulate anxiety are likely to have been shaped by selection pressures • Smoke detector principle where false alarms are cheap but ignoring a real warning might be deadly • Problem is that anxiety uses up time and energy, both which might better be spent elsewhere • Trait variation argument - anxiety disorder are mainly disorder of regulation that entail excessive or deficient responses • Time lag argument - some features of anxiety disorder would have has a rational basis in out ancient past Depression -An Epidemic of Modern Times? • Depression is a very common mood problem which has been growing at an alarming rate since the middle of the 20th century • Psychiatrists and clinical psychologists distinguish between endogenous/clinical depression and reactive depression • Reactive depression can be very severe but is considered to be a normal response to life events that would make anybody unhappy, such as bereavement or disappointment • Clinical or endogenous depression, however, is either considered to be unrelated to life events or is seen as an overreaction to them in its depth or longevity • The two main sub-categories are unipolar disorder and bipolar disorder • In unipolar depression there are generally alternating periods of depression and of relatively normal mood, whereas in bipolar disorder there may be alternative bouts of mania and depression which may be separated by periods of normal mood • Unipolar depression is far more common • Depression is the most researched area by proponent of Darwinian medicine • Three types of model which have been developed by by evolutionists to explain depression • Ultimate Causes 1. Depression is an adaptive trait Chapter 12: Evolutionary Psychopathology and Darwinian Medicine 2. Pleiotropy explanation 3. Trait variation explanation • Ultimate-Proximate Cause Interactions 1. Decline in social status 2. Failure to resolve interpersonal conflict model 3. Response to loss model • These explanations are by no means mutually exclusive • The Social Competition Hypothesis • John Price argued that mood, in general, plays an important role in human status hierarchies and that this may be related to the social conditions of our early ancestors • He suggested that depression is often observed in individuals who are unable to win a hierarchy struggle and yet refuse to yield • Price calls this the social competition hypothesis of depression • Price and his co-workers consider that when the voluntary yielding fails to occur then the state of depression, which would otherwise be transient, develops into prolonged depressive illness • Depressed Monkeys? • Evidence of a relationship between mood and status in vervet monkeys • Alpha males in each group had levels of serotonin which were twice as high as in low- ranking subordinate males • When such males lost their position, however, their serotonin levels fell dramatically • Interestingly, these behaviours were removed when the monkeys were given the antidepressant Prozac which boosts serotonin levels • Machiavellians and Moralists • Some studies of human social behaviour label males as either ‘Machiavellians’who are relatively aggressive and competitive individuals or as ‘moralists’who, in contrast, are more deferential • For Machiavellians social rank and serotonin levels are positively correlated, but for moralists there is a negative relationship between social rank and serotonin • Social competition hypothesis might even be criticized on the grounds that, with its emphasis on competition and status, it is a male-centered view of depression • Women do, however, also compete for status, albeit in a less overt way than men Is Depression Becoming More Common? • Young people are more likely to suffer from major depression than previous generations • Rates of depression were found to be higher in the richer societies than in the poorer ones • Proposing that certain novel aspects of modern life, which would not have occurred in our ancestral past, currently increase the likelihood of depression • Two such novel aspects have been proposed by Nesse and Williams - mass communication and disintegration of communities • Whereas in our ancestral past we
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