Depression is a low emotional state characterised by significant levels of sadness, lack of energy and self worth with feelings of guilt.
Depression in twins (genetics)
A biological explanation for depression is genetics. In the popuation around 5% have depression and so if depression is genetic we would expect twins to have a much higher concordance rate.
McGuffin et al (1996)- studied 177 twins with depression and the concordance rate was 46% for indentical twins and 20% for faternal twins suggesting depression has a substancial heritable component.
Depression in families (genetics)
Similarily we would exprect depression to run in families.
Gershon (1990)- found that rates of depression for individuals with a first degree relative with depression was about 2-3 times higher than in the general population.
Issues with twins and family
It's hard to seperate nature v nurture due to the sharing of the same environment which makes it hard to seperate environmental and genetic factors.
To overcome this we look at adoption studies.
Wender (1986)- biological relatives of sufferers of depression were 7 times more likely than their adopted relatives to have had major depression themselves.
Also, adopted children who develop depression, their biological parents were 8 times more likely to have depression than their adopted parents.
A problem with this is that we cannot generalise results to the general population as adoptive parents are often very motivated to care for their adopted children in a way different to natural parents.
Wihelm et al (2006)
Evidence that genes have a significant role within depression.
He interviewed 150 Australian teachers every 5 years for 25, asking them about positive and negative life events.
He found that negative life events were linked to depression and these individuals who had the short-short form of the serotonin transporter gene were particularily vulnerable to depression.
Egeland et al (1987)
Another study could also be linked to depression.
He studied the Amish who have a low incidence of depression.
One family had a high level of bipolar disorder and it was found that two marker genes on chromosome 11 were different.
These genes are involved in the production of a biochemical implicated in depression.
This study has not been replicated and so lacks reliability.
Psychological explanation- Freud
Freud said that depressed people repress anger towards the 'lost person' (to whome he identifies with) inwards towards themselves making them vulnerable to depression.
He said that childhood experiences also play a part, this was supported by Shah and Waller (2000).
Bifulco et al (1992)- Women who lost their mother as a child were more likely to suffer anxiety and depression as adults.
An issue with this is that according to psychodynamic principles, the repressed anger would emerge in dreams but Beck and Ward (1901) found no evidence for this.
Also instead of the anger being directed towards themselves...
Weissman et al (1971)- found that anger is usually directed to those around them.
Cognitive Theory (Learned Helplessness)
Seligman (1975)- depression can be explained by learned helplessness.
He placed a dog in a cage and when a electric shock came through the floor the dog would quickly jump over the barrier where there was no shock. If the barrier was too high to jump, he soon accepted the shocks were unavoidable.
When the barrier was lowered again, the dog still didn't try to escape- he had learned to be helpless.
This links to depresed people, they don't anticipate any change to the negative parts of their life.
An issue with this research is that it's done on animals and cannot be generalised to the human population.
Beck said that depression is due to negative self schema.
In Beck's Cognitive Traid it's explained that negative thinking leads to individuals paying more attention to the negative situations and ignoring the positive.
Lewinsohn (1981)- found from research that theres no relationship between negative thoughts and irrational beliefs and future depression.
Nolen-Hoeksma et al (1992)- although negative thoughts do make people more vulnerable to depression, there still needs to be an environmental trigger
Depression and other disorders
When evaluating the gentic theories, It may be that the genes that cause depression are also responsible for other disorders and so there may be a relationship between depression and other psychological disorders.
Kendler- found a higher incidence of mental disorders when looking at depression and anxiety suggesting people inherit a vulnerability for a range of disorders.
Wihelm et al (2006) supports this.
The 'Diathesis-stress' model
All explanations explained are inadequate just by themselves.
The diathesis-stress model explains the roles of genetics and the environment in depression.
The 'diathesis' is in the person (so for example the diathesis in Kendler's study of twins was a link between genetic predispositions)
The 'stess' comes from the environment (so in Kendler's study this was the negative life events).
Wilhelm (2006)- investigated this finding evidence that genes and the environment combine to cause depression.