The Evolutionary Advantage of Depression
More people die from suicide than from murder and war combined, throughout the world, every year. In the United States, suicide recently surpassed automobile accidents as the leading cause of violence-related death, according to a study appearing in the American Journal of Public Health.
The majority of individuals who commit suicide suffer from depression or another mood disorder. Depression is a devastating illness characterized by persistent sadness and myriad well-known symptoms. Increasingly, researchers are identifying how genes contribute to depression. As we learn more about the human genome, scientists are finding evidence that while depression seems incredibly maladaptive, it was actually adaptive (helpful) to our ancestors.
Recently Dr. Andrew Miller and Dr. Charles Raison, physicians at Emory University and the University of Arizona, respectively, authored a paper “The evolutionary significance of depression in pathogen host defense” in which they proposed that some of the alleles (forms of genes) that increase one’s risk for depression also enhance immune responses to infections.
Commenting on their hypothesis, Dr. Miller noted, “Most of the genetic variations that have been linked to depression turn out to affect the function of the immune system.” Dr. Charles Raison of the University of Arizona added, “The basic idea is that depression and the genes that promote it were very adaptive for helping people — especially young children — not die of infection in the ancestral environment.”
As recently as 1900, the top 3 causes of death in the U.S. were via infectious agents: pneumonia, tuberculosis, and diarrhea. Infants and young children were especially susceptible as 30.4% of all deaths occurred before the age of 5 years.