I feel like I've read a book that talked about reasons humans seem to have more diverse personalities amongst a sibling group compared to most animals. I'm afraid I can't remember what the book was or what it's conclusions were, though 🙁

I'm pretty sure there are studies that look at this though, in particular with twins, especially identical twins, as part of that old nature vs nurture debate.

I have 3 boys, they are all very different; the oldest is very academic, but he has issues relating to people; the middle one is kind and thoughtful, very imaginative and funny; the youngest is very physical, loves to play and push and just be active.

All of them are similar is a bunch of ways; but there are differences and I have to assume there is a genetic component.