Source: Time
By Jordan Raine, University of Sussex / The Conversation
Have you ever been sat on a flight with a crying baby in your vicinity, wondering more and more with each successive wail how much longer you can stand the sound? Or maybe you’ve been a parent, barely able to resist for a second before running to soothe your precious infant’s ear-piercing distress? Most of us have been there at some point in our lives. But what exactly is it about a baby’s cry that makes it so hard to ignore?
First, it is important to draw a distinction between crying and tears. Many species produce cries, but we appear to be the only animals that send emotional droplets streaming down from our tear ducts. While tears often accompany cry vocalisations in older age, they are by no means a prerequisite of crying – newborns cry from birth but don’t produce tears until they are two to three months in age. It also turns out that these early cries have evolutionary roots separate from the more cultural, learned “emotional crying” that we develop in later life.
Crying is a primitive behaviour shared across mammals, whose governing mechanisms are rooted in the evolutionarily ancient brain stem – infant rats, cats, and humans have all been shown to be able to cry even when the forebrain, which evolved much later, is absent. Indeed, the cries of many human and non-human mammal infants are highly similar in both acoustic structure and in the contexts in which they occur – across the mammal kingdom, infants cry primarily when they’re hungry, when they’re in pain, and when they’re alone.