Liars appear to have honey bunches more prefrontal white matter. You know, the stuff Autistics have dramatically less of. Lying is a lot more complex than telling the truth - but the liars studied still got caught and identified, or even admitted to being liars - does this make them bad liars? One figures the ability to white lie or even really seriously lie might offer evolutionary advantages, particularly for male reproductive strategy, where the 'getting caught' buffer would have less impact. One also suspects our culture probably has a major role to play on why we don't run around spouting utter bullshit to each other all day long - other studies I've seen suggest this may be assisted by belief in free will. I've always been kind of amazed at how many people seem to successfully maintain honesty in non-consequence situations, as well as how many bad liars don't even get it when you try to gently point out to them that you've caught them in their lie and the game's over.