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Biological Explanation of Phobias

Genetics and Evolutionary

Megan Stone

on 3 April 2013

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Transcript of Biological Explanation of Phobias

What is Inherited? It may be that people inherit an oversensitive fear response. Research shows that people with phobias often respond to normal situations with abnormal levels of anxiety.

The oversensitive response can be explained by the functioning of the autonomic nervous system. Some individuals may have abnormally high levels of arousal in the ANS leading to increased adrenaline, this is called the adrenergic theory. Twin Studies Twin studies are used to try to separate genetic factors from environmental factors. They examine the rate of concordance between monozygotic twins and dizygotic twins. Genetic Factors Some people acquire phobias whilst others do not, even if they have the same opportunities for learning, therefore suggesting that biology plays a role. Conclusion It is clear that phobic disorders aren't solely genetic, and they have some considerable environmental factor. This is known as the diathesis-stress model, genetic factors predispose an individual to develop a phobia, but environmental factors trigger the response.

It is important to remember the comorbidity between phobias and depression, which means that genetic factors may actually predispose an individual to a range of different mental disorders. Ancient Fears and Modern Minds Some stimuli may be more likely to be feared than others, such as storms, darkness, strangers and separation. These may be referred to as ancient fears, this is because they may have posed a real threat to our ancestors.
This theory states that most modern day phobias are exaggerations of these ancient fears.
Prepotency Experiencing anxiety after an event had happened would not have been an adaptive response, therefore animals have evolved to respond to potential threats.
Ancestors who were able to respond appropriately to ancient threats were more likely to survive and therefore pass on their genes.
Natural selection has shaped our nervous system so that we attend more to certain cues than others.

For example we are more likely to respond more anxiously to a loud noise or to a snake like object, this phenomenon is known as prepotency.
Prepotent fears are more likely to develop into phobias. Genetics and Evolutionary Biological Explanation to Phobias Research has shown that having a family member with a phobia increases the risk in the individual in developing a similar disorder.

For example, Fyer et al found that probands had three times as many relatives who had experienced phobias than normal controls. It is also found that the relatives usually have the same phobia as the proband.

For example Ost found that 64% of blood phobias had at least one relative with the same disorder. The main evidence on genetic factors in developing phobias comes from twin studies, although additionally some family studies have been carried out. Torgerson studied pairs of MZ and DZ twins where at least one of the twins had an anxiety disorder with panic attacks. The concordance rate was 31% for MZ twins, compared to 0% with DZ twins.

This therefore lends support to the genetic explanation to phobias, however this support is limited as the concordant twins did not have the same phobia. Torgerson AO1 Family and Twin Studies AO2 Family and Twin studies provide modest support for the genetic basis of phobic disorders, however there is considerable variability between disorders. Kendler et al Kendler estimated a 67% heritability rate for agoraphobia, 51% for social phobias and 47% for animal phobias.
However other studies find even less support for the genetic explanation such as Torgerson. One of the problems with family and twin studies is that they fail to control for shared environmental experiences.
For example MZ twins are likely to share more similar environments than DZ twins, as they are more likely to have the same interests.
One way to control for shared environment is to study twins who have been reared apart, however no such studies have been conducted on phobic disorders. Evidence has been accumulated to support the possible physiological differences between phobic individuals and non phobic individuals. Kagan Kagan identified an infant temperamental type that he described as 'behavioural inhibition' - infants who tend to draw away from unfamiliar people, objects and situations. He suggested that this behaviour had a genetic basis. Longitudinal studies have followed children who showed signs of behaviour instability at birth and have found they had higher ANS activity and the largest number of specific fears.

Similar results were found when looking at children whose parents suffered from a panic disorder. This therefore support that genetics may play a role in developing anxiety disorders. A further issue with twin studies is that they are not representative to the whole population, twins only account for 2% of the general population. Therefore we have to question the extent to which we can generalise findings from twin studies. Evolutionary This theory tries to account for why some phobias are more common than others. Ancient Fears and Modern Minds Prepotency Preparedness Preparedness Seligman proposed the concept of biological preparedness. This suggests that all species are innately prepared to fear and avoid certain stimuli because they are potentially dangerous.
We have evolved a preparedness to fear certain stimuli because such fears had survival value for our ancestors.
According to this idea, each species finds some kinds of learning much easier than others due to their biological predispositions.

Ohman and Soares
provided evidence for prepotency effects.
They conducted an experiment in which they showed participants images of feared objects that were not immediately recognisable. This shows that important components of phobic responses are set in motion before the phobic stimulus is represented in awareness. These could be prepotent signals. Participants who were scared of snakes or spiders showed greater GSR when briefly shown masked pictures compared to viewing neutral pictures. Garcia and Koeling Showed that rats could be conditioned easily to avoid life threatening situations such as poisonous liquids or shocks, but not to stimuli that had no bad consequences such as flashing lights. Therefore they were 'prepared' to fear dangerous stimuli. McNally McNally concluded that although there was firm evidence for enhanced resistance to extinction of fear responses conditioned by 'prepared' stimuli, evidence for rapid association was questionable. Davey Davey then proposed his theory of expectancy biases.
An expectancy bias is an expectation that fear relevent stimuli will produce negative consequences in the future.
Therefore there is no need to invoke past evolutionary history. This explains anomalous data such as the acquisition of modern phobias. Evaluation This theory can account for why certain phobias are more common than others.
It makes sense in evolutionary terms that were should be 'prewired' fear situations that are potentially dangerous.
Support for this theory can be found from failed attempts to condition children to fear inanimate objects using the same technique used to condition Little Albert to fear the white rabbit. It is less easy to see how this theory accounts for some unusual phobias such as phobia of buttons.
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