COMPARATIVE PSYCHOLOGY Evolutionary explanations of human behaviour

1. COMPARATIVE PSYCHOLOGYEvolutionary explanations of human behaviour EVOLUTION OF MENTAL DISORDERS

2. COMPARATIVE PSYCHOLOGYEvolutionary explanations of human behaviour • Researchers such as Nesse and Williams (1996) and Stevens and Price (1996) suggest that the existence and form of mental disorders can be explained using the same evolutionary principles that have been applied to account for the origin of other aspects of physiology and behaviour. EVOLUTIONARY EXPLAINATIONS OF MENTAL DISORDERS

3. COMPARATIVE PSYCHOLOGYEvolutionary explanations of human behaviour • The processes of genetic inheritance, evolutionary adaptation and the survival function of mentally disordered behaviour and emotion can be applied to explain: • Why they may have arisen in the first place – Evolutionary theory suggests that aspects of the behaviour or emotional reaction that appear disordered actually have important evolutionary survival functions and may in fact be shown to some degree by non – disordered members of the population. Mental disorders would therefore be linked to genes that have an adaptive function. CONT… EVOLUTIONARY EXPLAINATIONS OF MENTAL DISORDERS

4. COMPARATIVE PSYCHOLOGYEvolutionary explanations of human behaviour • Why they seem maladaptive – Mental disorders may cause maladaptive behaviour and an increase risk of death since they may: • Represent over – activity or excessive genetic expression of useful traits. • No longer be adaptive in the modern world. EVOLUTIONARY EXPLAINATIONS OF MENTAL DISORDERS

5. COMPARATIVE PSYCHOLOGYEvolutionary explanations of human behaviour • Why they still exist – Emotions and behaviours that are maladaptive should be ‘selected out’ and decreased in frequency by reducing the fitness of those showing them. However the mental disorders will persist if they: [1] Are strongly linked to genes for adaptive behaviour. [2] Do actually confer some benefit to genetic relatives (inc fitness). [3] Only result from genetic predisposition when triggered by environmental cues. [4] Have not had sufficient evolutionary time to disappear. EVOLUTIONARY EXPLAINATIONS OF MENTAL DISORDERS

6. COMPARATIVE PSYCHOLOGYEvolutionary explanations of human behaviour DEPRESSION There are two categories of depression unipolar and bipolar (manic depression). • Unipolar depression When might it be useful to feel depressed? • Lowered mood (sadness) is an appropriate response to certain situations. Nesse and Williams (1995) suggest that in certain situations it may be a better strategy to sit tight and do nothing. For example, our hunter-gatherer ancestors might have increased their survival if they were disinclined to venture out in bad weather but experienced low mood and stayed indoors. EVOLUTIONARY EXPLAINATIONS OF MENTAL DISORDERS

7. COMPARATIVE PSYCHOLOGYEvolutionary explanations of human behaviour • Unipolar depression cont… • The rank theory of depression suggests that it is important for survival that an individual who is the loser in a contest (i.e. loses rank) should accept the loss to prevent further injury from re-engaging his (or her) defeater, an act of damage limitation. • A further possible explanation for unipolar depression is based on the “genome lag” explanation. Nesse and Williams (1995) suggests that rates of depression are increasing and it is possible that depression is a consequence of life in highly developed, urban societies that are very competitive. People, especially young people, are presented with images of ideal lives and material possessions by the media. Such competition and longing leads individuals to feel depressed. EVOLUTIONARY EXPLAINATIONS OF MENTAL DISORDERS

8. COMPARATIVE PSYCHOLOGYEvolutionary explanations of human behaviour • Bipolar depression • There is a stronger evidence for the inheritance of bipolar depression than for unipolar depression. • Manic phase of bipolar disorder is related to creativity and charismatic leadership and thus would be an adaptive trait. • There is an endless list of famous people who suffer(ed) from manic depression: Winston Churchill, Abraham Lincoln, Vincent Van Gogh … … • The argument is that creativity is linked in some way to the same genes that underlie manic depression. WITHOUT ONE WE WOULD NOT HAVE THE OTHER. EVOLUTIONARY EXPLAINATIONS OF MENTAL DISORDERS

9. COMPARATIVE PSYCHOLOGYEvolutionary explanations of human behaviour ANXIETY DISORDERS Anxiety disorders are a group of mental disorders characterised by levels of fear and apprehension that are disproportionate to any threat posed. • Anxiety places animals in a state of arousal (the “fight or flight” response), ready to deal with an environment threat. • Anxiety also ensures that situations of danger are approached cautiously. • Such useful forms of anxiety can become crippling and disabling when anxiety becomes disproportionate to any problem experienced, such as in the case of phobias and obsessive-compulsive disorders. EVOLUTIONARY EXPLAINATIONS OF MENTAL DISORDERS

10. COMPARATIVE PSYCHOLOGYEvolutionary explanations of human behaviour Phobias • A phobia is a strong and irrational fear of something. • The emotion of fear may have some adaptive value. • Seligman (1970) used the term “preparedness” to describe the tendency for members of a species to be biologically predisposed to acquire certain conditioned responses. One response would be a fear of dangerous ‘things’, primitive humans would have a fear of insects, heights and small animals. EVOLUTIONARY EXPLAINATIONS OF MENTAL DISORDERS

11. COMPARATIVE PSYCHOLOGYEvolutionary explanations of human behaviour • Phobias cont… • Bennett-Levy and Marteau (1984) conducted a correlation study that supported the idea that we are born with a readiness to fear certain objects. • Participants were given a list of 29 animals asked to rate them in terms of ugliness, harmfulness and their own fear of the animal. • Fear was strongly correlated with the animal’s appearance e.g. number of legs or an unpleasant skin texture. EVOLUTIONARY EXPLAINATIONS OF MENTAL DISORDERS

12. COMPARATIVE PSYCHOLOGYEvolutionary explanations of human behaviour Obsessive-compulsive disorder (OCD) This disorder is characterised by a combination of obsessive thoughts and compulsive acts. • The compulsive rituals are often concerned with hygiene such as, washing oneself or cleaning for several hours each day to eradicate any possible contamination. EVOLUTIONARY EXPLAINATIONS OF MENTAL DISORDERS

13. COMPARATIVE PSYCHOLOGYEvolutionary explanations of human behaviour Obsessive-compulsive disorder cont… • One explanation offered for the cause of obsessive-compulsive behaviour is that the individual experiences intense anxiety form the obsessive thoughts. The hygiene ritual is found to reduce the anxiety and is thus rewarding, so as a result of operant conditioning the compulsive rituals are repeated. • From a evolutionary point of view there is an advantage in extra vigilance with tasks involved with cleaning and checking. EVOLUTIONARY EXPLAINATIONS OF MENTAL DISORDERS