The debate of whether nature or nuture is predominantly responsible for making each of us who we are has been around for a long time. Well, research has finally determined a clear answer here. It is a definitive “both!”
In his book, Incognito, David Eagleman, tells of research conducted in 2001 by Abshalom Caspi that shows a genetic link to depression, but whether or not that person actually develops depression depends on life events such as abuse, loss of a loved one, a serious injury, and the like. It was found that a specific gene regulates the brain’s level of serotonin which, in turn, is thought to directly regulate emotion.
A person has two copies of this gene, one from each parent. So, no one can totally blame just mom or dad here. There are three resulting possible combinations with which a person can end up, for example: short/short, long/short or long/long. Researchers discovered that the short/short combination predisposed a person to clinical depression, but ONLY IF they experience an increasing number of traumatic life events. (I think this is what happened to me.)
If people with the short/short gene combination were lucky enough to have an easy, calm life without too much trauma they were no more likely than anyone else to become depressed. However, if people were unlucky enough to have the short/short genes and ran into serious life difficulties, then they were twice as likey to become depressed as someone with the long/long combination.
In other studies, it was determined that a particular gene expression was significant in determing whether persons abused as children were likely to develop conduct disorders, become abusers, and commit violent crimes as adults. Even if experiencing a childhood of severe mistreatment, persons with the “good” genes would not necessarily grow into adults who continued the cycle of violence.
You inherit a genetic blueprint and are born into a world over which you have no choice throughout your formative years. This is the reason people come to the table with quite different ways of seeing the world, dissimilar personalities, and varied capacities for decision making. These are not choices; these are the dealt hands of cards. …[T]he machinery that makes us who we are is not simple, and science is not perched on the verge of understanding how to build minds from peices and parts.
So, when it comes to the nature or nurture question, it is clear that neither alone is responsible for determining a person’s personality.