Why are some humans cruel to people who don’t even pose a threat to them – sometimes even their own children? Where does this behavior come from and what purpose does it serve?

Humans are the glory and the scum of the universe, concluded the French philosopher, Blaise Pascal, in 1658. Little has changed. We love and we loathe; we help and we harm; we reach out a hand and we stick in the knife.

We understand if someone lashes out in retaliation or self-defence. But when someone harms the harmless, we ask: “How could you?”

Humans typically do things to get pleasure or avoid pain. For most of us, hurting others causes us to feel their pain. And we don’t like this feeling. This suggests two reasons people may harm the harmless – either they don’t feel the others’ pain or they enjoy feeling the others’ pain.

Another reason people harm the harmless is because they nonetheless see a threat. Someone who doesn’t imperil your body or wallet can still threaten your social […]