Evil

I believe environment has a lot to do with who we are. Genes and whatever else we're born with have a smaller part. Your actions now depend on your past and how you were/are treated by the world. If someone is abused as a child, they're more likely to abuse their children than someone who had a non-abusive childhood. What the world throws at people is what people will throw at the world even if that retaliation is years later. That's not always the case but it is most of the time. I don't think anyone is evil just to be evil. People normally have a good reason to do so. But it's like a chain reaction and the evil gets passed on and passed on whether it's a person's kids or friends or anybody they come in contact with.
I think karma plays a part too. We're paying for stuff that didn't happen in this life. But for the most part i believe how we behave is due to our youngest years. We are taught things about how the world is and it sticks with us. You can't teach a old dog new tricks. If the information we process in our heads as a child is misguided but we believe it, it becomes extremely hard to see the truth as we grow older. For example, if someone is told they are stupid over and over again as a little kid, they will believe it because they don't know better. That's why it takes so many therapy sessions to re-learn and re-shape what goes on in our heads.