There have been a lot of experiments on identical twins in the last century, to address the same question, nature or nurture. They were isolated and brought up in different families, countries etc. The conclusion was that BOTH nature and nurture play a role in a person's behavior, including gender roles and "pecking order" or social hierarchy. You may want to read a popular book on this and other related topics by Richard Dawkins, an english biologist of repute, called "The selfish gene". It is reasonably interesting and very educative.