Cutthroat greed and resource hoarding are traits common to many humans, but new research reveals that monkeys understand basic forms of wealth and will make moves to increase their own affluence amongst their tribe.

By considering water intake as a quantifiable measure of wealth among individuals in a tribe of rhesus macaques which had been trained in a simple gambling exercise, the researchers were able to observe the monkeys actively making choices that would enrich their own water supply. The study sought to understand whether monkeys share human risk attitudes and economic rationality, as well as how the possession of wealth - in this case water - alters risk-taking behaviors.

"We found that after training, monkeys are very rational. Just like humans, monkeys are able to select objectively better options from a menu of choices. If there is an alternative that offers better outcomes in all circumstances, they will go for it," said Agnieszka Tymula, from the University of Sydney School of Economics. "The monkeys also seem to share human risk preferences. They were slightly risk averse and we know that humans would behave similarly in these experimental conditions."

To test the monkeys, the researchers devised an experiment where the monkeys were presented with two pie charts, one symbolizing that they would receive a small but guaranteed amount of water, and the other symbolizing a (usually) greater water reward but with chance of receiving nothing at all. The amounts of water associated with the sure and risky options varied and were presented randomly.

In the experiments, monkeys that received less water would make much more cautious choices than their more water-satiated peers. Tymula and her colleagues found evidence of increased risk-taking amongst the "wealthier" of the monkeys, which she says suggests an "evolutionary link to human sensitivities around affluence level."

"Human sensitivity to wealth levels developed before the advent of money," Tymula said. "Understanding the biological mechanisms underlying risky behaviors that evolved around satiety may provide unique insights about decision-making and consumption wealth."

While the insights about monkeys' sense of wealth and their corresponding choices may draw some parallels to Wall Street and the stock market trading floor, replicating the study in humans will likely be difficult if not impossible.

"We would never have such control over water consumption among human populations; people often say one thing and do another."

Other authors of the study, which was published in Proceedings of the National Academey of Sciences,  included Hiroshi Yamada from the National Center of Neurology and Psychiatry in Tokyo, and Kenway Louie and Paul W. Glimcher, from the Center for Neural Sciences at New York University.