What chimpanzees can teach us about human friendships

Think back to years past. When you were a kid, you most likely had more friends than you do now. There were probably a lot of children on the playground you considered a friend, but not all of these friendships were very deep. As you grew up, your friendship circle most likely grew smaller. Instead of having many superficial relationships, you now have just a few really important friendships.

This is normal. When we are older, we tend to focus on maintaining positive, meaningful relationships. One idea suggests that we become more selective about our friends because we become increasingly aware of our own mortality. In other words, we have a future-oriented cognition. However, a recent study published in Science on the wild chimpanzees living in Uganda’s Kibale National Park suggests that our friendships may not actually be tied to thinking about the future.

Alexandra Rosati, an evolutionary psychologist at the University of Michigan and one of the study’s leads investigators, had heard about this long-term field study in Uganda. “It seemed like it all could sort of fit together, in this cool way, this primatology data to actually test this idea about human cognition,” she says.

In this study, a team of researchers analysed 78,000 hours of observations of 21 male chimpanzees made between 1995 and 2016 at the Kibale National Park. According to Rosati, a unique feature of this study is the value that exists in the long-term collection of data. “We used 20 years of data for this paper. [It] lets us look at this really detailed information about what's going on in these chimpanzees’ social lives,” she says. The findings surprised her.

Like humans, as these chimpanzees grew older, they increased the number of mutual friendships and decreased the number of one-sided friendships they maintained. In these mutual friendships, aged chimpanzees were more likely to groom each other, and they engaged in grooming for longer periods of time. This suggests these friendships were of high value to the chimpanzee.

These results throw into question some aspects of this idea known as the socioemotional selectivity theory. While humans have an impending sense of mortality, it is widely believed that chimpanzees do not. Because we are so closely related to chimpanzees, these findings in the wild chimps might also apply to people. But if future-orientated cognition isn’t the source of this shift in social behavior seen in both humans and chimpanzees, what is?

“We know it's very unlikely to be this future time perspective. So, we propose that it has something to do with changes in emotional reactivity,” says Rosati. Emotional reactivity refers to the tendency to react with intense, emotional arousal in a situation.

Now, Rosati and her team are using the same Kibale data set to investigate whether changes in emotional reactivity explain the recent findings from the male chimpanzees.

Joan Silk, a professor from Arizona State University who was not involved in the study, explained that it could be emotional reactivity, but that’s just a proximate explanation, distinct from an explanation of how something works. She says, “For me, a complete explanation requires a proximate explanation and what we call an ultimate explanation.... So, the question is: why would they be built that way?”

For me though, the question that lingered the most is why was everyone I talked to so quick to rule out future-oriented cognition in these chimpanzees? It seems that this research could be viewed instead through the lens of critical anthropomorphism, a concept that “helps to establish ground rules for dealing with the anthropomorphic tendencies that we, as sentient humans, confront in trying to understand the behavior of other species.” When we take this viewpoint, we assume that chimpanzees make conscious decisions about the nature of their private experiences, such as friendship dynamics.

Future planning, no matter what the species, requires a high degree of cognitive processing. However, it is readily apparent that many animals plan, at least in the short term, for the future. For instance, red squirrels plan their future litters based on their predictions about seed and nut yields. If squirrels can plan ahead like this, what are our evolutionary cousins capable of?

Chimpanzees show numerous signs of planning. For instance, in the 1960s Jane Goodall observed chimpanzees carrying tools to nut-cracking sites. Sometimes chimpanzees even plan for specific tasks and select the appropriate tools in anticipation of that task. But planning and forethought go even further than this in chimpanzees. Other more rigorous studies in controlled laboratory settings also suggest that chimpanzees engage in systematic, future-oriented cognition by overriding their immediate drives in favor of future needs, not simply relying on associative learning, and actively planning a task.

How can we measure the ability to travel mentally in time and imagine oneself in the future in an animal other than a human? Although traveling mentally in time is, without a doubt, a complicated cognitive skill, what makes this skill uniquely human? Does emotional reactivity also explain human shifts in friendship selection? These are questions that deserve further study and may shed important light on what it is to be human (as well as an ape).

The study by Rosati and her colleagues gives valuable insight into how natural selection shapes social relationship strategies as we age. This study is also stimulating because it makes one reconsider the nature of how humans think and behave. Answering questions like this is difficult because humans live such a long time. But what’s important about this chimpanzee study and other studies like it is that they provide long-term data on known individuals that live a long time. By studying other primates that live a long time, we can learn more about our own behavior.

According to Rosati, “I think a lot of the time people don't necessarily understand why people are out there in the forest collecting decades and decades of data. In part, that's because the value of this is to answer questions that haven't been asked yet.”

This is what stood out to me the most during my conversation with Rosati—this idea that old observations could be used to help one day to answer the questions that haven’t been asked yet. What questions will we be asking tomorrow?