Nature is loaded with odd traits and behaviors. There are elephant trunks, the widely separated eyes of hammerhead sharks, and the wacky, effervescent mating dances that sandhill cranes do. But nothing is quite as strange as human crying.
It does not seem odd to us, of course. We do it often enough ourselves and witness someone else doing it nearly every day. According to one study of more than 300 men and women conducted in 1980s at the University of Minnesota, women cry five times a month or so and men about once every four weeks. And the first thing a baby does when it enters the world is bawl to let everyone know it has arrived healthy and whole. It is not the howling itself that makes our crying unusual; it is the tears that go along with it. Other animals may whimper, moan and wail, but none sheds tears of emotion--not even our closest primate cousins. Apes do have tear ducts, as do other animals, but their job extends only to ocular housecleaning, to bathe and heal the eyes. But in our case, at some point long ago, one of our ancestors evolved a neuronal connection between the gland that generates tears and the parts of the brain that feel, sense and express deep emotion.