Ever let out a groan, bang your fist or scratch your head in frustration when life didn't go your way? Maybe you were forced to wait in line for a restaurant table, or you raced to the movie theater and found the show sold out.
Well, the same holds true for our closest living animal relative, the chimpanzee. In a study published Wednesday in the journal PLOS One, researchers concluded that chimps and bonobos both get emotional when life serves up bummers.
A three-minute wait for food, or a surprise helping of boring old lettuce instead of delicious banana slices, can inspire an epic tantrum of moans, screams, body scratching and hand banging, according to Duke University researchers.
Although most adult humans are able to regulate their emotions when faced with delays or disappointment, researchers say the basis of those feelings are rooted in our evolutionary past and played a fundamental role in the development of human decision-making.
Understanding what angers apes can provide insights into our own mental processes, according to the study authors, evolutionary anthropologists Brian Hare and Alexandra Rosati.
"Emotions play an important role in human choice processes," they wrote.
To see how disappointment and frustration played into the animals' decision making, study authors devised a series of experiments in which 23 chimpanzees and 15 bonobos were faced with various food-related dilemmas.
In some cases, the apes were offered two choices of food -- one of which might consist of a single slice of papaya, while the second choice had a greater number of slices.
In order to obtain the larger, preferred portion, however, the test subjects had to wait up to three minutes. (The above video shows a bonobo wrestling with his frustrations as he waits for the experimenter to serve up a larger portion of food.)
In another set of experiments, the apes were faced with a game of chance: They were given the choice of receiving a very small portion of food or a second mystery choice that they could not see.
Those apes who wanted to play it safe went for the first choice, while risk-takers opted for the concealed treat.
If the gamble paid off and the test subject received a large helping of their favorite fruit, there was little fuss. But if their wager resulted in a less desirable items like cucumbers or lettuce, they threw a fit, or tried to switch their choice at the last minute. (The experiments were conducted in separate ape sanctuaries in central Africa, and apes who showed no interest in playing the games were allowed to drop out of the study.)
Researchers noted clear differences between the two ape species. Chimps were much more willing to wait for food, and were much more likely to assume risk. The bonobos were less patient and more likely to go with the safe choice.
Chimps chose a risky reward about 65% of the time, while bonobos went for the mystery treat only about 40% of the time.
Study authors theorize the difference has to do with the animals' evolution and surroundings. Bonobos, they wrote, are accustomed to a more plentiful food environment, while chimpanzees face greater seasonal variability and competition for food.
"Our evolutionary hypothesis is therefore that feeding ecology has shaped psychology," study authors wrote. "Chimpanzees are more willing than bonobos to accept 'costs' to obtain food -- including in situations involving delays, travel time, effort, or risk -- thus promoting adaptive patterns of decision making in these species," the authors wrote.
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