It's more that exuberance is built into what we mean by the word extrovert, and there is a huge amount of psychological literature on extroversion.
Fraternal twins are no more likely to have this same exuberance than are other siblings in the same family.
Then is there a relationship--causal or otherwise--between exuberance and obsession?
Likewise, in the case of exuberance, when you find yourself with somebody whose arms are wide open, and they're laughing and full of joy, that's going to affect you too.
But Thoreau's exuberance bounces off the pages, and so does Muir's.
There's a real exuberance about the way we are as children.