Biological Explanations of Depression

 According to psychologists from a biological perspective, individuals may develop depression due to genetic inheritance. Children can inherit different types of the 5H77 gene from their parents, which is responsible for the transmission of serotonin, therefore having a history of depression in the family can increase ones chance of developing it. This is known as genetic predisposition.  In support of this Harrington et al found that people who share a 50% genetic relationship with someone with depression have a 20% of developing the disorder, compared to 50% of the general population. This highlights strong evidence confirming the biological explanation of depression, since it supports the basic prediction of genetic theory. However, although the genetic explanation makes sense at face value, many people who have a family history of depression never go on to develop it, and people with no family history of the disorder can develop it, therefore genetics cannot be the sole explanation for depression.   

 Nonetheless, the findings from Adoption Studies can be applied to support the genetic argument. Wender et al studied adopted children with depression and found that their biological relatives were 7 times more likely to have depression than the adoptive relatives. This further suggests that there is a genetic factor in depression, and although other adoptive studies have found a relatively weak correlation when studying this they have found a similar result. 

 Additionally, twin studies have proven to be effective in investigating the possible link between genetics and depression, where one twin would have the disorder and to investigate the likelihood (concordance rate) of the other twin having it. McGuffin et al found a 46% concordance rate among Mz (identical) twins, compared to 20% among Dz (non-identical). Both these rates are dramatically higher than the general life time risk of developing depression, applied to the general population, however due to the fact that the concordance rate is not 100% this study therefore again highlights that genetics cannot be the sole explanation for depression. One must also consider the environment the twins were raised in, which could be a contributory factor to why they may develop depression.

 Neurotransmitters can play a significant role on the development of depression; dopamine and noradrenaline are said to be the main ones involved in depression. It has been found that low levels of noradrenalin can lead to depression, and high levels can lead to the mania's depressive symptoms and suicidal tendencies. Additionally, the serotonin theory suggests that high levels of serotonin can lead to depression.

 In support of this, Martin et al found impaired serotonin levels transmitting in people with depression, which of course accepts the basic predictions of the serotonin theory. 

 Rosen et al presented evidence supporting biochemical theory through comparing the substances found in urine samples of depressed people and a control group. It was found that compounds produced as a by-product of the action of enzymes activating serotonin and noradrenalin were present in smaller amounts of the depressed urine. This shows the impact neurotransmitters can have in depression.

 Depression can also occur due to hormonal imbalance. Depressed people tend to have high levels of cortisol, which can lead to depressive symptoms such as suicidal thoughts, and low levels of noradrenalin means that the hypothalamus is unable to regulate these levels. If these levels are not lowered by the means of drugs, the depression lifts.  

 In support of this, psychologist Suomi has been studying rhesus monkeys in order to measure the effect of genes on depression. Through this he has found that 20% of monkeys are born with a genetic tendency to depression and anxiety, and in a laboratory environment they produce cortisol when experiencing stress. On the other hand, whether or not these monkeys develop depression in later life depends on the attachment formed with their mothers. 

 Unfortunately this study holds several weaknesses which make it difficult to apply to humans as well as the real world. Firstly the fact that much of the research was conducted under artificial settings in a laboratory gives it low ecological validity due to the control over extraneous variables, making the findings inapplicable to a real life situation. Furthermore, a huge disadvantage within this study, and the biochemical explanation of depression in general, is that 
much of the studies used to support its proposals are not only unethical due to the use of animals but also anthropomorphic. It is therefore difficult to extrapolate the findings in hormonal imbalance from non-human animals to that of humans, as we are said to have a far more complex brain structure and live in a more social and emotional world. Contrary, some psychologists, particularly from an evolutionary perspective, would argue that the same characteristics apply across species. 


(I've highlighted the bit on anthropomorphism because its key to learn when writing an essay. Loads of research studying loads of different approaches use animals, which you'll see through further reading and revision, so remembering this sentence can significantly maximise your Ao2, as well as make your essay sound a lot more fluent and sophisticated.)