Before you read Blink, or Nudge, or Twitch, or Blurt, or any other popularization of the latest research into human behavior glance through the articles in the Fall 2011 Journal of Economic Perspectives.  You will find that the science trying to find the physiological source of human behavior is still very new, and plagued with results that can't be reproduced.

If that's too heavy, you can read this article in the Journal of Serendipitous and Unexpected Results that finds positive reactions to scenes of human social interaction in the brain of a dead salmon.  (Or at least check out the brain scans of the dead fish.)

I confess that I am prejudiced against the line of research claiming to find that this gene or that section of the brain is responsible for altruism or risk-taking.  In college I took intro to psych from two old-school psychoanalysts.  We read R. D. Laing; we read Alice Miller.  One time, one of them remarked that every year or so he read about some area in the brain being linked to schizophrenia or some other disease,  yet nothing ever seemed to come of it.  On the list things I heard in college that have influenced (or haunted) me ever since, that has to rank in the top 10, maybe the top 5. 

One time, in a previous job, I met with mental health advocates convinced, convinced, that the science was all figured out; that the biological basis of mental disease was settled; that if the government just made the insurance companies help pay for the meds, things would be better.  Not the confrontational type,  and several years out of school, I only expressed the very slightest skepticism. 

But my old psych teacher still looks to be right.