"That's just me, that's who I am." Ever say that? Some of us are completely sure of who we are, some of us search all of our lives for a good answer to "why am I like this?"
Scientist and author Bill Sullivan can help answer that question. But it's a long-ish answer that includes things like DNA, environment, even microbes.
The full story is contained in Sullivan's book Pleased to Meet Me. We grab the author for a tour of the factors that make us US.