Patience, self-control and delayed gratification
How long would you wait for six grapes? A chimpanzee will wait more than two minutes to eat six grapes, but a black lemur would rather eat two grapes now than wait any longer than 15 seconds for a bigger serving.
According to Jeffrey R. Stevens University of Nebraska-Lincoln psychologist, "Natural selection has shaped levels of patience to deal with the types of problems that animals face in the wild. Those problems are species-specific, so levels of patience are also species-specific."
Published in the scientific journal Proceedings of the Royal Society B, Stevens studied 13 primate species from massive gorillas to tiny marmosets, comparing species' characteristics with their capacity for "intertemporal choice."
What he discovered was that species with bigger body mass, bigger brains, longer lifespans and larger home ranges were willing to wait longer.
Chimpanzees, averaging about 85 pounds, living approximately 60 years in a 35 square mile range will wait for about 2 minutes, longer than other primates studied. Weighing less than a pound, with a 23-year lifespan, cotton-top tamarins will wait only eight seconds before opting for the smaller, immediate reward.
Lemurs, marmosets, tamarins, chimpanzees and bonobos were used to conduct the decade long study at Harvard's Department of Psychology, the German based Berlin and Leipzig zoos. Individual animals were offered a tray containing two grapes for immediate consumption or a tray containing six grapes to be eaten after waiting. Wait times were gradually increased until the animal reached an "indifference point" when it opted for the smaller, immediate reward instead of waiting. Stevens combined his results with results of similar experiments that gathered biological characteristic data of each species.
Stevens also analyzed two other hypotheses for patience: cognitive ability and social complexity, but found no correlation.
"In humans, the ability to wait for delayed rewards correlates with higher performance in cognitive measures such as IQ, academic success, standardized test scores and working memory capacity," he wrote. "The cognitive ability hypothesis predicts that species with higher levels of cognition should wait longer than those with lower levels."
Researchers have long debated about the correlation between complex social groups and reduced impulsivity, providing adaptive behaviors to support dominant and submission based social hierarchies, but found no evidence. He believes metabolic rates to be the driving factor connecting patience with body mass and related physical characteristics. Smaller animals tend to have higher metabolic rates.
"You need fuel and you need it at a certain rate," he said. "The faster you need it, the shorter time you will wait."
Read more at the University of Nebraska-Lincoln.