Let's return to evolution. Are humans the only species with the capacity for self-deception?
No, I do not think so. Lying is widespread throughout the animal kingdom, both between species and also within species. One example is mimics, species that are harmless and tasty but gain protection by resembling a poisonous or distasteful one. Psychologists are getting close to showing that monkeys practice self-deception.
Like humans, monkeys naturally associate members of their “in-group” with positive stimuli such as fruits, and out-group members with negative stimuli such as spiders.
Do children come into the world as self-deceivers or does it take a while to develop?
That is very tough to say. There's evidence that deception in children starts at six months of age. By eight or nine months they have developed the ability to deny that they care about something that they do care about. But demonstrating self-deception is tricky.
Is it right that self-deception is correlated with intelligence?
Yes, at least for deception. The smarter your child is, the more he or she lies. In monkeys, the bigger the neocortex is, the more often they're seen lying in nature.
Robert Trivers is one of the world's best-known evolutionary biologists. His latest book is titled The Folly of Fools: The Logic of Deceit and Self-Deception in Human Life.