It's been argued that the human mind thinks by means of accumulating data or by means of genetics. Although, in my opinion, I'd say it could have been on both terms too. I mean, I've once did a little session of recalling all my past, including how I behave, and my personality. Truth be told, I was so different when I was a kid back then. In Myers-Brigg terms, I'd say I was ENFP before. But I drastically became INTJ (online test-based). But then, even with the changes and turns in my life, my way of thoughts were the same back then. Either it improves for the better, or forgets/devolves some of my lines of thinking as life goes on. I think there is already a character in us since birth, but consequently, it's our choice whether or not to accept or reject them and/or learn/unlearn to the things we perceive.
To be perfectly honest, the way of our minds is unknown, which is in a way stunningly intriguing, but it creeps me out all the same.