Primate Hoarding
Once someone owns something, he places a higher value on it than he did when he acquired it. “The endowment effect” has been seen in hundreds of experiments, the most famous of which found that students were surprisingly reluctant to trade a coffee mug they had been given for a bar of chocolate, even though they did not prefer coffee mugs to chocolate when given a straight choice between the two.
The effect is not universally observed. Whereas coffee mugs generate an endowment effect, tokens that can be exchanged for coffee mugs do not.
Owen Jones and Sarah Brosnan suspect that, in the evolutionary past, giving things up, even when an apparently fair exchange seemed to be on offer, was just too risky. To test their theory, they have been training chimpanzees to trade (see “Law, Biology, and Property” — pdf file here).
When presented with a choice between peanut butter and frozen juice bars, 60% of the chimps preferred peanut butter to juice. However, when they were endowed with peanut butter, 80% of them chose to keep it instead of exchanging it for juice. And an opposite endowment effect was observed when the chimps were given juice.
Before they started work Jones & Brosnan predicted that the strength of the effect would vary with the evolutionary salience of the item in question. As predicted, when they tried the same experiments using bone and rope toys, no endowment effect was seen. Food is vital. Toys are not.