Humans differ from other animals in a variety of ways. One of the most impressive is what Marc Hauser (here) calls “fluid thinking,” the “brain’s capacity to repeatedly combine thoughts and emotions from different domains of knowledge” (189-90). I discussed the conjecture by Liz Spelke and others that human linguistic competence underlies this (here), though at the moment it is, I believe, fair to say, that this hunch has remained pretty underdeveloped and has yet to rise to the level of a full fledged hypothesis. Nonetheless, even in its inchoate form it is interesting to consider the possible properties (both ben- and mal- ign) of a combinatorial demodularized brain when hooked up with an apish neuro-chemistry. Hauser, in a fascinating book with the tasty title Evilicious, does this for the problem of evil. Yes, you read correctly, this is a big theme book. What makes it impressive, is that it not only spins a hellishly good story, but is didactic and, in addition, a pleasure to read (well sort of, the topic can get pretty disgusting, e.g. see p. 151-2 and p. 205 for a partial inventory of torture methods and instruments).
Hauser starts with the common observation that humans are very good at being very bad. In fact, compared to other animals we are in a league of our own when it comes to inflicting gratuitous pain for gain and/or pleasure. Hauser gives a tour of the underlying psycho-biology of this capacity for cruelty and provides a pretty suggestive story that links our neuro-chemistry (there’s nice reviews of the various effects of testosterone, serotonin, dopamine etc), brain modules (e.g. the anterior cingulate plays an important role), genetics (there’s some action on the X chromosome that is critical) and our emergent mental fluidity (in part a product of our promiscuous and recent evolved combinatorial capacity (think Merge)) to explain why psychopathic behavior is so natural to humans. Nothing does cruelty, like humans do cruelty. And the same goes for sadism, torture, rape, mass murder, auto-da-fes, stoning, genital mutilation, etc. In effect, the same features that support our remarkable creativity have had the unfortunate consequence of giving us the capacity for evil unparalleled in the rest of the biological world. The road from Da Vinci (or even Ghandi) to Ghengis Kahn is shorter than you might like.
Oddly, the book, at least to me, has a 17th-18th centural feel to it. Hauser writes a bit like how Hume might have written were he among us today. How so? Evilicious is a piece of natural philosophy, combining a deep knowledge of what we have learned in the mental and brain sciences (btw, the footnotes are a great resource all by themselves. Damn he’s read and synthesized a lot!) to explain how people are able to insulate themselves from moral considerations so as to be able to act in unboundedly many heinous ways without even hints of remorse.
There is also a touch of Leibniz-Malebranche. Like them, Hauser aims to explain how evil is the natural concomitant of those human virtues we all prize: imagination, a sense of justice and desert, a taste for risk, etc. To steal a line from Jan Koster, what Hauser shows is how evil is a human App; it’s what you get when you get the kinds of flexible combinatorial brains that allow for human creativity. This argument would have delighted Leibniz and Malebranche in their theodicean moments. But how depressing to think that this might really be the best of all possible worlds (capacity wise at least (see Hauser's nice distinction between evolved repertoires vs evolved capacities p. 230)).
So, Hauser has written a terrific little book. It synthesizes and reviews, in a very readable way, a lot of contemporary research in evolutionary biology, neuro-chemistry, neuro-science, social psychology, philosophy, economics and more. And it does this all the while addressing one of those endlessly fascinating questions: whence evil? I highly recommend it. Reading it might even be good for you.