https://www.scientificamerican.com/article/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 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.