Where does suicide fit in the course of human evolution? Has natural selection been, so to speak, against suicide, or accepting of it, or indifferent to it?
We might hope that evolution is gradually finding suicide to be disadvantageous and is pushing it aside. That seems reasonable because suicide appears contrary to evolution’s prime directive to pass on one’s genes or to assist one’s kin in doing so. As Cornell anthropologist Meredith Small has put it in “Why Doesn’t Evolution Discourage Suicide?” “When young people kill themselves, their genes are eliminated from the gene pool; when adults kill themselves they can no longer care for dependent children; when elderly people kill themselves, they, too, abdicate the role of caring parent for the next generations.” At every age, suicide interrupts genetic continuity.
But—apart from the fact genetic change rarely happens quickly—unfortunately suicide shows no signs of slacking off. (Recently in Russia, an average of five adolescents killed themselves every day). One obstacle is that suicide is not traceable to a single trait that can be selected against. Moreover, some of its key components are very desirable traits, such as sensitivity to the opinions of others and the ability to imagine the future.
If natural selection has not been selecting against suicidal individuals, perhaps it has been selecting in favor of them for some reason, or did so for the tens of thousands of years prior to our historical era. Perhaps, at a reproductive level, the suicidal person’s relatives were in some ways better off after he or she was dead.
One version of this thesis was that of Denys deCatanzaro in the 1980s. As summed up by Scientific American blogger Jesse Bering, the idea is that “Human brains are designed by natural selection in such a way as to encourage us to end our own lives when facing certain conditions, because this was best for our suicidal ancestors’ overall genetic interests.” Which conditions? A person might believe, rightly or wrongly, that he or she is a burden to the family, will not have children of his or her own, or can not make any positive contributions to the family or society. Such people, the theory goes, would all be most prone to suicide and their family in the long run would be better off as a result. Perhaps such self-selection was true enough for long enough in the past that it still operates today.
A difficulty with this theory is that suicide is linked not just to family and reproductive issues but to a wide range of mental, physical, and social problems. The list of conditions correlated with suicide is long: addictions, imprisonment, chronic pain, unemployment, brain injury, most mental disorders, abuse as a child, suicidal parents, peer pressure, post-traumatic stress disorder, low serotonin. While many of these conditions might limit one’s capacity to contribute to others, they don’t point noticeably towards a family being better off as the result of a suicide.
Natural selection’s third option concerning suicide, and possibly the most likely, is indifference. Perhaps, on the whole, the killing of the self out of misery neither harms nor improves the fit between humans and their environment. And the number of suicides has probably not been large enough to make a difference in our long-term development as humans, for one thing. Moreover, isolated, sickly and self-destructive thoughts and acts are the products of the same brains that make an individual happy and healthy. Suicidal moods have been likened to very destructive weather: the same atmospheric forces that create an exquisite day can, in the right combination, result in a disastrous one. After all, we all have the capacity for the acute sense of social failure along with the intense preoccupation with the self that sets the stage for suicide.