What does studying how animals relate to each other tell us about human friendships?
At its simplest, it’s just how critical quality social bonds and friendships are. In animals, the big measures that evolutionary biologists study are reproductive success, which they count as either how many babies you have or how long those babies live, and longevity, or how long you survive. Nonhuman primates have very structured hierarchies that they exist in, and everyone assumed that that must have more importance for how long you live and how many babies you have and how healthy they are. And it wasn’t. The most important thing was the strength of the social bonds, how positively and well and regularly an individual animal interacted with other animals. Scientists really couldn’t believe it.
How does friendship affect physical health?
Friendship literally improves your body’s cardiovascular functioning, how your immune system works, how you sleep. You can imagine the food you put in your body makes you healthy or not. But sitting in a coffee shop with someone and just chatting about what’s going on with your life, we always thought emotionally that made you feel good. But actually it really is doing much more.
A big study at Harvard of men across their lives from 20 to 80 found that the single best predictor of your health and happiness at 80 was not your wealth or your professional success. It was your relationships at 50.