One of the most controversial questions pertaining to psychology has always been whether people gain their behaviors from Nature (genes) or Nurture (environment). There are examples of both cases out there. One example of our behaviors coming from our environment is the behaviors of feral children like the one shown below. This is some evidence that environment does play a large role in behavioral traits because although the kid has human genes, its behavior mimics that of its host parents (the animals).
An example the provides evidence for the Nature debate is the study of twins, especially identical ones separated at birth. One case is of 2 guys who had identical likes, dislikes, wife's name, ex-wife's name, dog's name, and even their first kid's name.
Something really surprising for me was the question of whether homosexuality was inherited or developed throughout their environment. Studies have indeed found that it is more likely that homosexuality is biological than environmental. Evidence for this is if an identical twin is homosexual, there is over a 50% chance that the other one is as well. Studies have also shown that homosexuality is developed early in a childs lifecycle, possibly even before birth.
This video I found really was interesting to me, I think it is just a couple kids that had a presentation to make but i really learned a lot from it and it let me understand the topic a lot better. http://www.youtube.com/watch?v=IPZsrLAkpKM&feature=related