Simon Baron-Cohen in InCharacter:
In moral terms, honesty is without doubt a virtue, and dishonesty is a vice. But in social terms, absolute honesty can lead to trouble, risking causing offense to others who may not want or need to hear the complete truth. White lies may be desirable. And in biological terms, dishonesty is a sign of typical brain development, whereas someone who is incapable of dishonesty may be neurologically atypical. Dishonesty is one defining characteristic of what it is to be human. It is not the only defining characteristic, but it does separate us from other animals. Some nonhuman species may have a limited capacity for deception, but humans have a flexible, unlimited capacity for deception. And since anything that is uniquely human is likely to be part of our genetic makeup, it stands to reason that we are, in a sense, built for dishonesty — and those incapable of dishonesty, like people with autism, have a uniquely human disability. Beyond having deficits in social interaction, they live with a different relationship to morality. Their experience is a unique window into the typical human mind.
We’ll return to this point in just a moment. But before we can see what honesty means for being human, and what we can learn about it from autism, we need to take an unexpected detour and examine first what other species can and can’t do when it comes to deception. To understand how humans lie, it profits us to begin by looking at monkeys.