It doesn't add up

The experimenters then changed the conditions. In a second trial, the monkeys were given additional tokens to trade for food, only to discover that the price of one of the food items had doubled. According to the law of supply and demand, the monkeys should now purchase more of the relatively cheap food and less of the relatively expensive food, and that is precisely what they did. So far, so rational. But in another trial in which the experimental conditions were manipulated in such a way that the monkeys had a choice of a 50% chance of a bonus or a 50% chance of a loss, the monkeys were twice as averse to the loss as they were motivated by the gain.

Remarkable! Monkeys show the same sensitivity to changes in supply and demand and prices as people do, as well as displaying one of the most powerful effects in all of human behavior: loss aversion. It is extremely unlikely that this common trait would have evolved independently and in parallel between multiple primate species at different times and different places around the world. Instead, there is an early evolutionary origin for such preferences and biases, and these traits evolved in a common ancestor to monkeys, apes and humans and was then passed down through the generations.

If there are behavioral analogies between humans and other primates, the underlying brain mechanism driving the choice preferences most certainly dates back to a common ancestor more than 10 million years ago. Think about that: Millions of years ago, the psychology of relative social ranking, supply and demand and economic loss aversion evolved in the earliest primate traders.

This research goes a long way toward debunking one of the biggest myths in all of psychology and economics, known as "Homo economicus." This is the theory that "economic man" is rational, self-maximizing and efficient in making choices. But why should this be so? Given what we now know about how irrational and emotional people are in all other aspects of life, why would we suddenly become rational and logical when shopping or investing?

Consider one more experimental example to prove the point: the ultimatum game. You are given $100 to split between yourself and your game partner. Whatever division of the money you propose, if your partner accepts it, you each get to keep your share. If, however, your partner rejects it, neither of you gets any money.