To a certain extent, there is still much debate over which has more direct influence in a child’s personality development. The argument goes as follows. There are certain genetic predispositions that affect how we develop into who we are. This is the nature side of the argument. Parents do pass on some personality traits to their children, as well as physical traits that affect personality. For example, a child that is tall might grow to be more confident than a child who is short. Children who are naturally thin may also develop more self-confidence than those who are predisposed to weight gain. Children of alcoholics are often predisposed to become alcoholics themselves.
The other major influence on a child’s personality comes from the way the child is raised. This is definitely a factor, and in most cases has a larger influence than genetics. Consider the above example of children of alcoholics. Yes, they have a definite genetic predisposition in some cases. However, the children are also raised in an environment of alcohol consumption. They also have easy access to alcohol. So it is a learned behavior as well as a genetic predisposition. Children who are taught to be calm and polite, and have behavioral models, will often be calm and polite. Nature has a strong influence, but so does nurture.
Genetic predisposition indicates that a child is more likely to develop a personality trait. It may not mean that a child definitely will. Yet there are some cases where identical twins are raised completely apart and end up more similar, even down to the same cereal choices. That is determined to be a genetic influence. Identical twins raised together might make intentionally divergent choices, that is they might actively choose to make their personalities different.