Genes that predispose someone to depression are only expressed when they are repeatedly exposed to stressors
If you have “the gene” (or genes) “for” depression, then is depression inevitable? Obviously not, and the best evidence for this is to consider identical twins. One has depression and the other, sharing all the same genes, has about a 50 percent chance of having the disease as well, a much higher rate than in the general population. There, pretty solid evidence for genes being involved. But flip this the other way. Share every single gene with someone who is depressive and you still have a 50 percent chance of not having the disease.
This is because gene expression is highly contingent on the environment. Those undergoing significant stress are more likely to develop depression, and genes increase the risk of depression, but only in certain environments: you guessed it, only in stressful environments. This is shown in a number of ways, but most dramatically in a study by Avshalom Caspi at King’s College, London. Scientists identified a certain gene in humans that increases the risk of depression. More specifically, it is a gene that comes in a few different “allelic versions”—a few different types or flavors that differ slightly in function; have one of those versions, and you’re at increased risk.
So having version X of this gene Z doesn’t guarantee you develop depression, it just increases your risk. And, in fact, knowing nothing more about someone than which version of gene Z someone has doesn’t increase your odds of predicting whether they gets depressed. Version X increases depression risk only when coupled with a history of repeated major stressors. Amazingly, the same has been shown with studies of some nonhuman primate species, who carry a close equivalent of that gene Z. It’s not the gene that causes it. It’s that the gene interacts with a certain environment. More specifically, a gene that makes you vulnerable in a stressful environment.
References
- Sapolsky, Robert. (2004). Why Zebras Don’t Get Ulcers Chapter 14. Stress and Depression (p. 414). New York, NY: Henry Holt and Company.
Metadata
Type:🔴 Tags: Biology / Genetics / Neuroscience / Psychiatry Status:☀️