Summary: genetics and environment are not mutually exclusive in conferring risk factors for depression; the answer may come from the interplay between the two variables in your response to stress.
Depression is a disabling mental illness. According to the Diagnostic and Statistical Manual of Mental Disorders (5th edition), the most common symptoms of depression are sadness, fatigue and anhedonia (i.e. the inability to feel pleasure in pleasurable activities).
Moreover, depression profoundly interferes with a person’s life. It impairs the ability to function at school during childhood and in society during adulthood. In its severest form, depression can lead to suicide . Globally, depression represents a public health challenge affecting over 300 million people, and by 2030, it will be the most significant cause of disability in the world (World Health Organization, 2017).
There is an urgent need to raise awareness as well as to educate people about the potential reasons leading to depression. One example is the response to stress (i.e. how your body physiologically reacts to a stressor), which receives influence from the interplay between genes and environment. Nevertheless, there are still one-sided arguments out there.
The social argument
A researcher called David Buss designed a correlational study between participants’ self-report (i.e. what people say) and behavioural measures (i.e. what people do). He wanted to analyse mate selection (i.e. how people choose their partners). Buss reported a positive correlation between the two factors, which indicates that personality is often consistent with behaviour .
Why is this relevant to stress and depression? If personality correlates with behaviour, then people who consistently live in a stressful environment and present sad mood are potentially depressed. In his study, Buss describes three mechanisms driving the positive correlation between personality and behaviour, which you may identify in people with depression:
- Selection. The deliberate choice and gathering between similar people as well as avoiding those who are different (e.g. depressive individuals are more likely to seek depressive-like individuals). The selection mechanism also applies to the environment (e.g. depressive individuals are more likely to avoid energetic places, such as a party).
- Evocation. This mechanism refers to individuals who unintentionally elicit specific behaviour from others. (e.g. depressive children evoke more attention from their parents; whereas active children evoke a strict parental control).
- Manipulation. The unaware modification of surrounding environments to address one’s personality (e.g. depressive individuals may decorate their homes and workplace with darker colours).
These mechanisms and patterns seem obvious, but most of us are unable to notice them. Moreover, social studies that attempt to address biology-based disorder must be interpreted with caution. The combination of the three mechanisms do not offer certainty; it only increases the likelihood of developing depression. Correlation does not mean causation.
Therefore, social arguments alone are unlikely to provide a reliable and valid answer. One-sided analysis struggle to report normative measures enabling clinical treatment of depression (e.g. cognitive behavioural therapy). As a consequence, correlational studies are more likely to maintain the status quo, rather than providing a solution.
The interplay with genetics
Gene-environment interaction is the link between two variables arising from the effects of one variable changing conditional to the other.
Let me unpack this for you.
The interaction between your genes and the environment occurs when genetic factors influence the body’s responses to the environment (or whatever happens around you). The environment cannot directly alter gene sequences. However, genetic effects, such as the ability to cope with stress, are dependent on gene expression . For example, the fight or flight response varies from one person to another.
Two factors influence gene-environment interaction:
- Spontaneous mutations. Each person inherits 50% of genes from her mother and 50% from her father. However, along the process, there are genetic mutations that make you different from your parents. These include changes which you cannot ‘see’, such as the production level of gonadal hormones under a stressful state. So, let’s get used to thinking beyond ‘eye colour’.
- Population changes. The changes in the frequency of a gene in a population. For example, a native tribe living in a remote location with no external interference is more likely to maintain similar characteristics. In this case, it creates a genetic bottleneck and some diseases never disappear from a population. Conversely, in a metropolis like London, there is more genetic variation.
Therefore, the environment you live in can relatively interfere with your genetics expression, mainly through your ability to cope and respond to stress.
King’s College London researcher Robert Plomin reports that the environment accounts for over 50% of the population variance of depression . Thus, changes in the environment play a significant role in heritability compared to the role of genetic mutation alone. Below are some elements that affect your stress-response and increases the chances of depression:
- Risk factors. Social and Economic Status triggers a stress response (e.g. worry and anxiety).
- Social interaction. Parenting style, loneliness or a poor workplace environment.
In other words, it is likely that a person with a negative genetic predisposition to stressful reactions become depressed living in a hectic and chaotic environment. So, taking some time to identify stressful triggers in your environment as well as particular behavioural patterns may prevent mental illnesses, such as depression.
Despite the efforts to understand the overall scenario conferring risk of depression, one-sided analysis is not an effective way to solve the problem. Instead, an individual analysis would be far more effective. The interplay between genetics and environment is an insightful source of information. Your stress-response to the environment you live might be a key player in developing depression.
 Gunnell, D., Kidger, J., & Elvidge, H. (2018). Adolescent mental health in crisis.
 Buss, D. M. (1987). Selection, evocation, and manipulation. Journal of personality and social psychology, 53(6), 1214.
 Rutter, M. (2010). Gene-environment interplay. Depress Anxiety, 27(1), 1-4.
 Plomin, R., DeFries, J. C., Craig, I. W., & McGuffin, P. (2003). Behavioral genetics. American Psychological Association.
Lau, J. Y. F., & Eley, T. C. (2010). The Genetics of Mood Disorders. Ann Rev Clin Psychol, 6, 313-337.
World Health Organization (2017). Depression and other common mental disorders: global health estimates.
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