Anne Darwin was a "lying bitch", according to her son Mark. He and his brother had grieved and supported her over the disappearance and likely death of their father - her husband - only to learn, six years later, that their parents had enacted an elaborate hoax.
How could the sons not have known, some have asked. Folk wisdom has it you can tell when people are lying. They scratch their noses, over emphasise words or look shifty.
But, says the psychologist Paul Ekman, a world authority on mendacity and author of Telling Lies, we are actually bad at detecting liars. Yes, there are minute facial muscle movements that coincide with intent to deceive, but most of us, he maintains, fare no better than chance in detecting falsehood through facial expression.
Honesty in life partners, friends and political leaders is consistently highly rated in surveys and polls. So why have we not developed the ability to detect dishonesty? Ekman suggests that our evolutionary history has not prepared us to catch out liars. When people lived close to one another, there would have been few opportunities to deceive. We would have had no need to develop skills in spotting liars.
Ekman also thinks that we may actually prefer not to catch people out lying, since life is far more enjoyable when we trust each other. Always doubting family, friends and colleagues would be an unpleasant way to live.
Thus, we suspend disbelief.
So where does that leave politicians? It is part of our cultural mythology that politicians lie all the time, while it is equally part of Westminster mythology that they don't. The prohibition against calling a fellow member of parliament a liar is what led Winston Churchill to offer the circumlocution that an honourable member had uttered a "terminological inexactitude".
And, despite our belief that public figures deceive us frequently, the consequences of being exposed as a liar can be extremely harsh, usually involving resignation and frequently out of proportion to the benefits gained by deception. Thus, Jonathan Aitken later said of the lie that led to his downfall: "It did not seem at that time a terribly important lie, at least in relation to the lies I was accusing others of telling about me. It was a lie about who paid a $1,500 hotel bill of mine in the Ritz Hotel in Paris while I had been a government minister." But he went too far when he brandished the "simple sword of truth" against the Guardian. The paper did uncover the truth and Aitken went to prison.
Perhaps the monstrous private deceit of the Darwins and the public falsehoods of politicians have this much in common. We expect to be lied to, maybe often, and choose not to challenge the perpetrators. But there is an unspoken contract. If you demand trust because of your office or accept the rewards that go with honesty in personal relationships, then, once you are caught lying, you will have forfeited all sympathy.