Do monkeys self-deceive?

In a fascinating column, John Tierney writes:

The Yale experiment was a variation of the classic one that first demonstrated cognitive dissonance, a term coined by the social psychologist Leon Festinger. In 1956 one of his students, Jack Brehm, carted some of his own wedding gifts into the lab (it was a low-budget experiment) and asked people to rate the desirability of things like an electric sandwich press, a desk lamp, a stopwatch and a transistor radio.

Then they were given a choice between two items they considered equally attractive, and told they could take one home. (At the end of the experiment Mr. Brehm had to confess he couldn’t really afford to give them anything, causing one woman to break down in tears.) After making a choice (but before having it snatched away), they were asked to rate all the items again.

Suddenly they had a new perspective. If they had chosen the electric sandwich press over the toaster, they raised its rating and downgraded the toaster. They convinced themselves they had made by far the right choice.

So, apparently, did the children and capuchin monkeys studied at Yale by Louisa C. Egan, Laurie R. Santos and Paul Bloom. The psychologists offered the children stickers and the monkeys M&M’s.

Once a monkey was observed to show an equal preference for three colors of M&M’s — say, red, blue and green — he was given a choice between two of them. If he chose red over blue, his preference changed and he downgraded blue. When he was subsequently given a choice between blue and green, it was no longer an even contest — he was now much more likely to reject the blue.

I would distinguish between self-deception and an endowment effect.  We value more what is ours, perhaps because of our biological programming -- to protect our children above those of others -- spills over into decisions more generally.  (Or perhaps because of a precommitment strategy to limit violent plunder of our resources.)  Self-deception is then layered on top, but in fact many mothers will argue that their kids are lazier or less obedient than the average.  The endowment effect holds nonetheless, as those mothers care more about their kids.  It is very hard to switch back babies once the hospital makes a mistake in allocation (how much time must elapse?), even if the parents know for sure they did not take home the genetically appropriate little bundle of joy.

I can see that the monkeys behave according to an endowment effect.  I am less sure that the monkeys self-deceive.  The key question, in my view, is whether the monkeys would throw out or downgrade information that some other bundle of food was in fact better than M&Ms.