Answer
And studying identical twins raised apart is one of the most effectives ways we can use twins to understand the origins of personality. And it is striking. I’ve studied reared apart twins for ten years, and we find that despite the differences in the homes, the twins are quite similar in many personality traits – from extraversion, to dominance, to aggressivity. And this does strongly underlie the fact that personality is, to a substantial degree although not entirely, influenced by our genetic factors.