Many people will say it is morally acceptable to pull a switch that diverts a train, killing just one person instead of the five on the other track. But if asked to save the same five lives by throwing a person in the train’s path, people will say the action is wrong. This may be evidence for an ancient subconscious morality that deters causing direct physical harm to someone else. An equally strong moral sanction has not yet evolved for harming someone indirectly.

For more, read The Happiness Hypothesis, which earned a Starred Review from Publishers Weekly:

The spirit is willing but the flesh is weak, lamented St. Paul, and this engrossing scientific interpretation of traditional lore backs him up with hard data. Citing Plato, Buddha and modern brain science, psychologist Haidt notes the mind is like an "elephant" of automatic desires and impulses atop which conscious intention is an ineffectual "rider." Haidt sifts Eastern and Western religious and philosophical traditions for other nuggets of wisdom to substantiate—and sometimes critique—with the findings of neurology and cognitive psychology. The Buddhist-Stoic injunction to cast off worldly attachments in pursuit of happiness, for example, is backed up by Mihaly Csikszentmihalyi's studies into pleasure. And Nietzsche's contention that what doesn't kill us makes us stronger is considered against research into post-traumatic growth. An exponent of the "positive psychology" movement, Haidt also offers practical advice on finding happiness and meaning. Riches don't matter much, he observes, but close relationships, quiet surroundings and short commutes help a lot, while meditation, cognitive psychotherapy and Prozac are equally valid remedies for constitutional unhappiness. Haidt sometimes seems reductionist, but his is an erudite, fluently written, stimulating reassessment of age-old issues.