How patient a primate is may depend entirely on how it has evolved. Primates with larger bodies appear to be more willing to wait for large rewards, compared to smaller species who prefer immediate gratification. One researcher claims that these observations may help us better understand the patience of humanity as well.

A study published in the Proceedings of the Royal Society B details the potential evolutionary reasons why different species of primates have different levels of patience.

Study author Jeffry R. Stevens, a comparative psychologist at the University of Nebraska-Lincoln (UNL) spent 10 years studying 13 different primate species and their capacity for patience. According to Stevens, the benefits of patience vary from species to species, and so, levels of patience, or "intemporal choice," will vary as well.

" [P]roblems are species-specific, so levels of patience are also species-specific," Stevens explained in a UNL press release.

After analyzing primate behavior in controlled experiments, Stevens found that the larger their body, territory, and lifespan, the longer a primate species was willing to wait for a large reward, compared to smaller species who preferred immediate-but-small rewards.

According to the study, these experiments determined a primate's patience by having it choose between a tray containing two grapes that could be eaten immediately, or a tray with six grapes that could be eaten after waiting. Each time a primate chose to wait, the grapes were rewarded, and the next wait was made longer. This was repeated until the primate reached an "indifference point" at which it would choose the smaller reward over the extended wait.

The results were coupled with past results from similar experiments to form a database for a comprehensive analysis of primate behavior.

According to the UNL press release, Stevens had expected patients to be most highly dependant on cognitive performance, as humans associate the concept of "mind-over-body" with  patience. However, this was not what the analysis showed.

Metabolic rates, Stevens explained, may be the most important factor in patience. Smaller animals, regardless of their intelligence, are less likely to wait because their tiny bodies hold less energy that they burn quickly. Having more patience or a mind that can overrule bodily needs may actually starve some species in these situations. Thus, natural selection may have favored the impatient.

"To me, this offers us interesting avenues to start thinking about what factors might influence human patience," Stevens said.

The study was published in Proceedings of the Royal Society B, on May 14.