Chimpanzees and human teenagers can both be ruthless

Chimpanzees and human teenagers can both be ruthless

Human teenagers aren’t exactly known for their aloofness. An imperfectly developed region of the brain called the ventromedial prefrontal cortex (vmPFC), which acts a bit like a parking brake, can make adolescents more likely to engage in risky behaviors, such as reckless driving, substance abuse, and risky sexual behavior. It turns out the same is true for juvenile chimpanzees, except that reckless behavior might look more like heightened aggression to them.

A study published on January 23 by the Journal of Experimental Psychology: General from the American Psychological Association notes that while chimpanzees and teenagers share these risk-taking behaviors, the chimps may be less impulsive.

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“Adolescent chimpanzees are in some ways exposed to the same psychological storm as human teenagers,” said co-author Alexandra Rosati, associate professor of psychology and anthropology at the University of Michigan, in a statement. “Our results show that several key features of human adolescent psychology are also found in our closest primate relatives.”

Chimpanzees can live up to 50 years, and their puberty begins around the age of eight to 15 years. Chimpanzees exhibit rapid changes in hormone levels during puberty, form new bonds with their peers, show some increase in aggression, and compete for social status just like their human counterparts.

In the study, the research team conducted two food reward trials on 40 wild-born chimpanzees at the Tchimpounga Chimpanzee Sanctuary in the Republic of the Congo in central Africa. It included 21 men and 19 women, ranging in age from six to 25 years, with a mean age of 15 years.

In test number one, adult and adolescent chimpanzees performed a gambling task and were given a choice of two containers. One of the containers always contained peanuts, which chimpanzees love so much. The other had either an unloved snack (a slice of cucumber) or his favorite, a slice of banana. They had a choice of playing it safe and getting some kind of delicious peanut, or risking getting the coveted banana at the risk of getting a nasty pickle.

The team recorded the chimps’ vocalizations and emotional responses, including moans, screams, whimpers, pounding on the table, or scratching. To track hormone levels, they also collected saliva samples.

Adolescent chimpanzees chose the risky option more often than the adults, but both expressed negative reactions when given the cucumber.

Test number two was modeled after Stanford’s famous marshmallow experiment, which was conducted on human children to study delayed gratification. The chimpanzees could either get a banana slice right away or wait 60 seconds to get three tasty banana slices.

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Adult and adolescent chimpanzees both chose to delay gratification at a similar rate. In this situation, human teenagers tend to be more impulsive than adults and would be more likely to choose instant gratification.

“Previous research shows that chimpanzees are quite patient compared to other animals, and our study shows that their ability to delay gratification matures at a relatively young age, unlike humans,” Rosati said.

What differentiated the juvenile chimpanzees from the adults was that they threw more tantrums than the adults during the delay.

According to Rosati, risky behavior appears to be biologically ingrained in both adolescent humans and chimpanzees, but some increase in impulsive behavior may also be more of a human thing. In addition, future studies could examine differences in impulsive behavior in male and female chimpanzees.

“We are currently investigating the development of several other cognitive skills in chimpanzees, including self-regulatory skills and the emergence of social skills that help chimpanzees form and maintain relationships,” Rosati said PopSci in an email.

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