Who doesn’t know the difference between right and wrong? Yet that essential knowledge, generally assumed to come from parental teaching or religious or legal instruction, could turn out to have a quite different origin.

Primatologists like Frans de Waal have long argued the roots of human morality are evident in social animals like apes and monkeys. The animals’ feelings of empathy and expectations of reciprocity are essential behaviours for mammalian group living and can be regarded as a counterpart of human morality. Marc D. Hauser, a Harvard biologist, has built on this idea to propose that people are born with a moral grammar wired into their neural circuits by evolution. In a new book, Moral Minds (HarperCollins 2006), he argues that the grammar generates instant moral judgments which, in part because of the quick decisions that must be made in life-or-death situations, are inaccessible to the conscious mind.

The proposal, if true, would have far-reaching consequences. It implies that parents and teachers are not teaching children the rules of correct behaviour from scratch but are, at best, giving shape to an innate behaviour. And it suggests that religions are not the source of moral codes but, rather, social enforcers of instinctive moral behaviour.

Both atheists and people belonging to a wide range of faiths make the same moral judgements, Hauser writes, implying “the system that unconsciously generates moral judgments is immune to religious doctrine.” Hauser argues the moral grammar operates in much the same way as the universal grammar proposed by the linguist Noam Chomsky as the innate neural machinery for language. The universal grammar is a system of rules for generating syntax and vocabulary but does not specify any language. That is supplied by the culture in which a child grows up.

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