Why we cry - the evolutionary science behind our natural reaction

Professor Sophie Scott of University College London studies cognitive neuroscience of human communication. She is well-known for her TED Talk called, "Why We Laugh." We asked her to explain why humans cry. Following is a transcript of the video.

Sophie Scott: As far as we know, we are the only species that produces tears.

Hi, my name's Professor Sophie Scott and I'm based at University College London where I study the cognitive neuroscience of human communication.

So, other animals show anger, other animals show signs of sadness, other animals show aspects of laughter. We are the only animal also, across, occasionally all of these examples, who produces fluid in our tear ducts.

Tears are there to keep your eyes moist. And that's doing that job across many different sorts of animals. In us, we also produce these excess tears and that seems to be some kind of further emotional mark - possibly of intensity. There's even been an argument that there may be a different chemical makeup to your tears depending on your emotional state. And maybe that has a communicative element. We still don't really know. All we do know is that we are probably the only animal that genuinely weeps.

There's quite an interesting literature on crying, so crying with sadness, a sort of sobbing sound. I always assumed that people didn't do it unless they absolutely had to 'cause I personally hate crying and I feel terrible when I've been crying. But, there is a very robust literature showing that the majority of people - about 80% of people - feel better when they've been crying. And that's true of men and of women.

And it seems to be something people will do to make themselves feel better. They will do that to improve their mood. Now, I find that absolutely unbelievable because I feel, I'm off for about a day if I've been crying. It just ruins the rest of the week for me. But, data is data and I have to accept that people who try and hold it back and not do it, may actually be the ones who don't like crying and the rest of the world is full of people who actually get a good feeling from crying.

We do also know that, cross-culturally, there are big variations in how much different cultures cry. So, in our culture in the UK right now, we don't often see people crying. We particularly very rarely see adults and men crying. Now that is quite a recent development. If you go back 150-or-so years, crying wasn't just a more common behavior, it was an appropriate behavior in many different situations, but, in fact, it was a sign of sophistication and emotional ability in men.

So, a man who cried was a man who had sort of genteel emotions and who could feel pain in a civilized way. So, that's gone and we, if somebody shows any sign that they're crying in public life nowadays, we tend to really freak out. But that's still just us. You can go to parts of the world where it's extremely common for people in public life to cry to express shame or embarrassment or to fully apologize for something.

So, these behaviors, these emotions that we can find in common across humans and across other examples in other animals - doesn't mean to say we all use them in exactly the same way. We develop them and repurpose them and use them quite culturally specific ways as well.