In this episode, guest Professor Joshua Greene and host Charlie Bresler hit upon an important question — and have somewhat different answers.

Many of us claim to be pretty “moral” human beings with an admirable set of values. But do we always live up to it? Obviously not, or we likely wouldn’t need police or lawyers or jails. The question Josh and Charlie found thornier is the why. Why don’t we live up to our professed values?

According to Charlie, it seems we simply learn to suppress our better angels when they aren’t convenient or comfortable. Sure, it may cause cognitive dissonance to pass by a hungry homeless person, but somehow we manage.

For Josh, the reason may be more embedded in our survival instinct. We have evolved to live in relatively small groups of friends and family, and our nobler intentions don’t always extend beyond that circle. Universal cooperation just isn’t in our genetic makeup.

Which is it? Nature, nurture, or a smidge of both? Whatever, the larger question here — and the one they agree on — is how do we overcome our smaller, more selfish behavior to help anyone in need?

Josh Greene is an experimental psychologist, neuroscientist, philosopher, and professor at Harvard University . He studies how humans make moral judgments and decisions, but includes a very science-based perspective: primarily behavioral experiments and functional neuroimaging (fMRI). He is the author of Moral Tribes: Emotion, Reason, and the Gap Between Us and Them.