I recently finished Thérèse Raquin by Emile Zola. I'm hoping to read more of Zola's work. I share his view that humans are purely mechanistic beings whose behavior is caused by genetic and environmental factors. In fact, I've been looking for good authors who explore determinism in their work; looks like I've found one. I think I'll read La Bête Humaine next.
I'm currently reading The Origin of Species.