Are people born evil or the world makes them evil?

I had been wondering about this issue for months. This started with the words echoed in the Film: 'Ticking Clock' :"If you are given a chance to go back in past and kill Hitler in his early childhood will you do it?" I started wondering about this and questioned a number of people that whether people are born(genetically) evil or the become evil by the way life treats them. Your valuable opinions specially of those studying neurons, DNA and similar stuff are welcomed,!!???