Ask HN: Books on human nature that changed your interactions

http://futurepositive.synearth.net/leader-follower/

I found something akin, not so much "interactions" as in understanding the "why" about many human things, in reading Richard Dawkin's The Selfish Gene.

Saint-Simon's memoirs.

Neither really for theories as such, the latter for reflections on the the behavior observed.

Since wturner mentions "Blood Rite" let me throw in Vico's "New Science"