- * One weakness of the genetic explanation is that there is a problem of the nature-v-nurture argument. It is difficult to separate out the influence of nature and nurture. Whilst the twin studies provide strong evidence for the role of genetic factors and the adoption studies point to the role of nature over nurture this is not conclusive.
- * A major criticism of the genetic explanation of depression is that most of the twins and other family members in the studies on which the evidence is based were brought up together in a common environment. Twins also share a common pre-natal environment. This is a problem because it makes it impossible to separate the effects of genetics from the effects of learning. (Behaviourists would favour the learning argument to explain depression). This suggests that perhaps the validity of twin and family studies is questionable which weakens the genetic argument.
- * A final problem is that there is an issue with population validity. The reason for this is because the samples used in such studies are so small and therefore there is difficulty generalising the results to the rest of the population.
- * One strength of the biological explanation of depression is that there is further empirical support provided by Ogilvie et al. (1996). They showed that cells use a gene called SERT to make serotonin transporter protein which plays an important role in the transmission of information between neurons. In most people, part of this gene called the second intron contains 10-12 repeating sections of DNA. However, people with depression, only have 9 repeating sections of DNA. This suggests that there is wider academic support for the idea that serotonin is strongly associated with depression.
- * One weakness of the biological explanation of depression is that there are individual differences. Not everyone who suffers from depression is helped by serotonin-based drugs, which suggests that there are other causes of the disorder. It is also not clear why some people become depressed when their serotonin or norepinephrine level is low, whereas others with the low neurotransmitter level remain depression-free. This suggests that the results gained from such research cannot be generalised to the whole population.