Today the way we consider human psychology and mental development is heavily influenced by the genetic sciences. We now understand the importance of inhereited characteristics more than ever before. Yet we are still unable to decide whether an individual's personality and development are more influenced by genetic factors (nature) or by the envrionment (nurture).
Research, relating to identical twins, has highlighted how significant inherited characteristics can be for an individual's life. But whether these characteristics are able to develop within the personality of an individual surely depends on whether the circumstances allow such a development. it seems that the experiences we have in life are so uNPRedictable and so powerful, that they can boost or over-ride other influences, and there seems to be plenty of research findings to confirm this.
My own view is that there is no one major influence in a person's life. Instead, the traits, we inherit from our parents and the situations and experiences we have in life are constantly interacting. It is the interacting of the two that shapes a person's personality and dictates how that personality develops. If this were not true, then we would be able to predict the behaviour and character of a person from the moment they were born.
In conclusion, I do not think that either nature or nurture is the major influence on a person, but that both have powerful effects. How these factors interact is still unknown today and they remain largely uNPRedictable in a person's life.