Do you agree that depression can be heritable?
Being a victim of bullying during childhood is another factor in early life environment related to depression. Ttofi et al. conducted a systematic review of longitudinal studies investigating whether the relationship between being a victim of bullying in school and later depression remains after controlling for other childhood risk factors for depression. They found the likelihood of being depressed even up to 36 years later was significantly greater in those who had experienced bullying. Being bullied remained a significant risk factor for depression even after controlling for several other childhood risk factors. These results indicate that being a victim of bullying during childhood is an independent contributor to future depression.
All of the above evidence supports the idea that depression has its origins in early life environment. However, it’s not just environmental factors that can lead to depression; there are also biological factors such as genetics. The genetic explanation argues there are certain genes which predispose individuals to depression. Thus depression can be inherited. Studies of twins have supported this idea, McGuffin et al. found concordance rates of 46% for monozygotic (identical) twins opposed to just 20% for dizygotic (fraternal) twins. However, with twin studies, genetics cannot be separated from environmental factors. Adoption studies remove this limitation, Wender et al. found that the biological parents of adopted children who had depression were eight times more likely to also have it than their adoptive parents. Thus, supporting the idea of depression being heritable and refuting the idea that the environment alone causes depression.
As well as factors in early life environment, there are also factors that occur in mid to late life that can cause depression. For example, there is evidence to suggest that prolonged unemployment can lead to depression. Stankunas et al., in a cross-sectional study, found that those in long-term unemployment had experienced more periods of depression the past year than those who had only been unemployed for a brief period.
To conclude, the evidence suggests that depression can originate in early life in some cases, but the early life environment cannot account for all cases of depression. For example, not everyone who has an insecure attachment or suffered ACEs develop depression and not everyone with depression has an insecure attachment or had a traumatic childhood. The most likely conclusion is that depression can originate at different time points influenced by a range of biological (e.g. genes) psychological (e.g. self-esteem) and social factors (e.g. family) that intertwine and together cause depression.