This is an old question, is it nature or nurture... The answer is: yes. By which I mean, it is both. Something like your eye colour is clearly due to genes alone but most things including height or behaviour are influenced by both. I am 188cm tall, I needed to have the genes for that but if I were born into poverty for instance and I didn't get the appropriate nutrition as a child then I would never have reached 188cm. The example is height but it applies to the vast majority of things aside from the simple things like eye colour. Behaviour is of course a complex issue and as such, it seems this would be the case here and in fact it is. Twins are an excellent example, they have identical genes but they become different heights, they have different personalities, one may develop medical conditions etc.
As I said, almost everything (including behaviour) is a combination of the two.