The fact that such a big environmental factor doesn't effect personality at all, to me suggests that personality is mostly genetic. Anecdotally, It sure seems like kids have very distinct personalities from a very start.
Another anecdote (that personality is more nature rather than nurture), is the stories of identical twins adopted to different families. When reunited as adults, they seem to have the same personality. One such story:
> "It's not just our taste in music or books; it goes beyond that. In her, I see the same basic personality. And yet, eventually we had to realize that we're different people with different life histories."
> "Contemporary empirical research shows that birth order does not influence the Big Five personality traits."
https://en.wikipedia.org/wiki/Birth_order
The fact that such a big environmental factor doesn't effect personality at all, to me suggests that personality is mostly genetic. Anecdotally, It sure seems like kids have very distinct personalities from a very start.
Another anecdote (that personality is more nature rather than nurture), is the stories of identical twins adopted to different families. When reunited as adults, they seem to have the same personality. One such story:
> "It's not just our taste in music or books; it goes beyond that. In her, I see the same basic personality. And yet, eventually we had to realize that we're different people with different life histories."
https://www.npr.org/2007/10/25/15629096/identical-strangers-...