Moral Minds: How Nature Designed Our Universal Sense of Right and Wrong
By Marc D. Hauser
Little Brown ₤25, 512 pages
FT Bookshop price: ₤20

The nature-nurture debate has moved on to the human sense of morality. Marc Hauser, a Harvard University psychology professor, believes that over millions of years we have evolved an instinctive feeling for right and wrong. This provides a fundamental blueprint for all societies, however much their moral codes differ in detail.

Hauser’s inspiration is the revolution in thinking about linguistics over the past 50 years. The intellectual godfathers of his work are Noam Chomsky, who proposed in the 1950s that a “universal grammar” lies at the heart of the human language facility, and then John Rawls, the political philosopher who believed that an inbuilt moral grammar underlies human behaviour. The literary model for Moral Minds is Steven Pinker’s The Language Instinct (1994).

But Hauser is not blessed with Pinker’s wonderful writing style. Moral Minds is hard going for those without a firm grasp of moral philosophy and who do not enjoy books sprinkled with words such as “deontological”.

Hauser creates three hypothetical individuals to symbolise different ways of distinguishing right from wrong. The Kantian Creature follows reason not emotion. The Humean Creature follows his heart then comes up with a moral justification later, if necessary. And the Rawlsian Creature relies on instinctive moral analysis of the causes and consequences of his actions.

However, Hauser could have gone straight for the Rawlsian approach without consistently dismissing Kant and Hume.

The author brings to bear a vast mass of evidence. He discusses thought experiments in different cultures which show similar instinctive reactions to moral dilemmas. He shows how brain damage and psychopathic illness affect moral sensibilities. And he describes research into the behaviour of animals, from bees to chimpanzees.

To get readers thinking about their instincts, Hauser borrows a series of thought experiments from moral philosophy. Imagine a tram hurtling out of control towards five pedestrians. If you could flick a lever to switch the tram on to a track with just one person, is it permissible to kill one to save five? The almost universal answer is “yes”.

Then think of yourself on a bridge above the track. Now the only way to stop the tram is to push down a heavy object - and there is one beside you, in the form of a fat stranger. Again you can kill one person to save five, but this time the moral consensus is that it would be wrong. There are significant philosophical differences between the cases - for example the distinction between “foreseen harm” (indirectly killing the lone pedestrian by flipping a switch) and “intended harm” (directly pushing the fat man to his death). Most people cannot articulate such distinctions, Hauser says, but they feel them instinctively.

Hauser is most interesting when he writes about animal behaviour. Many species show signs of a primitive moral sense. But most of our moral instinct seems to have evolved in the six million or so years since humans diverged from apes.

Hauser attempts only a weak explanation of the evolutionary processes that might have been responsible. He hints that there may be a role for group selection, an idea favoured by Darwin but rejected by most evolutionary biologists today, who emphasise individual genes. Compared to other animals, people show far more variability between groups and cohesion within them - and this might allow group selection to have played a significant role in human evolution.

Compared to the ambitions of its author and publisher, Moral Minds is a disappointment. Ultimately it comes across as a lengthy statement of the obvious.

Clive Cookson is the FT’s science editor