Aetiologies of unipolar depression:
Biological explanations suggest that depression could be a consequence of genetic factors. Evidence to support this comes from family, adoption and twin studies. For example, McGuffin et al (1996) found a concordance rate of 46% for monozygotic twins compared with only 20% for dizygotic twins. A problem is that twins share similar environments (e.g. if a family member dies or parents divorce). MZ twins will often share a more similar environment and upbringing than DZ twins. Therefore, this evidence does not necessarily mean that the disorder is entirely genetic. Furthermore, since concordance rates do not even come close to 100%, depression cannot be entirely genetic, and therefore there must be an environmental element to depression.
One criticism of the biological theories is that they are biologically determinist because they suggest that we are unable to change because we have no control over such biological factors - we can't change our genetics. Another criticism of biological theories is that they are reductionist because they ignore environmental factors, such as major life events. However the diathesis-stress model suggests that some people possess a genetic predisposition to depression. This genetic predisposition may then be triggered by environmental stressors (such as death of a loved one, financial difficulties) to produce a depressive reaction. Evidence to support this model comes from research which has found that while depression is linked to negative life events, individuals from genetically high-risk groups are the most likely to become depressed. The advantage of this theory is that it is an interactionist theory because it takes account of both nature and nurture.
One explanation of depression is that it is caused by deficiencies in the neurotransmitters noradrenaline and serotonin. Support for this comes from the fact that depression is effectively treated by drugs that increase the availability of serotonin/noradrenaline in the brain. However, anti-depressants are not effective in the treatment of all cases of depression. Anti-depressants also have effects on many other neurochemicals, apart from noradrenaline…