The moral grammar too, in Hauser’s view, is a system for generating moral behaviour and not a list of specific rules. It constrains human behaviour so tightly that many rules are in fact the same or very similar in every society—do as you would be done by; care for children and the weak; don’t kill; avoid adultery and incest; don’t cheat, steal or lie.

Matters of right and wrong have long been the province of moral philosophers and ethicists. Hauser’s proposal is an attempt to claim the subject for science, in particular for evolutionary biology. The moral grammar evolved, he believes, because restraints on behaviour are required for social living and have been favoured by natural selection because of their survival value.

Much of the present evidence for the moral grammar is indirect. Some of it comes from psychological tests of children, showing that they have an innate sense of fairness that starts to unfold at age 4. Some comes from ingenious dilemmas devised to show a subconscious moral judgment generator at work. These are known by the moral philosophers who developed them as “trolley problems”.

Suppose you are standing by a railroad track. Ahead, in a deep cutting from which no escape is possible, five people are walking on the track. You hear a train approaching. Beside you is a lever with which you can switch the train to a sidetrack. One person is walking on the sidetrack. Is it OK to pull the lever and save the five people, though one will die? Most people say it is.

... contd.