wiley | Friendship pervades the human social landscape. These bonds are so
important that disrupting them leads to health problems, and
difficulties forming or maintaining friendships attend neuropsychiatric
disorders like autism and depression. Other animals also have friends,
suggesting that friendship is not solely a human invention but is
instead an evolved trait. A neuroethological approach applies
behavioral, neurobiological, and molecular techniques to explain
friendship with reference to its underlying mechanisms, development,
evolutionary origins, and biological function. Recent studies implicate a
shared suite of neural circuits and neuromodulatory pathways in the
formation, maintenance, and manipulation of friendships across humans
and other animals. Health consequences and reproductive advantages in
mammals additionally suggest that friendship has adaptive benefits. We
argue that understanding the neuroethology of friendship in humans and
other animals brings us closer to knowing fully what it means to be
human.
