What Science Reveals About Why We Cry : Short Wave Last month, Short Wave explored the evolutionary purpose of laughter. Now, we're talking tears. From glistening eyeballs to waterworks, what are tears? Why do we shed them? And what makes our species' ability to cry emotional tears so unique?

Why Do We Cry?

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You're listening to SHORT WAVE from NPR.




KWONG: You and I both knew this episode was coming.

SCOTT: Yeah. Ever since we did an episode on why we laugh, I knew we'd have to have the twin episode, why we cry.

KWONG: On balance, it just felt right. And there is one actor who gets me choked up more than anyone.


TOM HANKS: (As Chuck Noland) Wilson. Wilson.

KWONG: Tom Hanks in anything - in this case in "Cast Away," in most of "Apollo 13," "Saving Private Ryan."

SCOTT: Emily, Emily, I can only imagine watching the end of "Forrest Gump" with you, where he's at Jenny's grave and telling her about their boy.


HANKS: (As Forrest Gump) He's so smart, Jenny. You'd be so proud of him.

KWONG: It gets me every time.


HANKS: (As Forrest Gump) If there's anything you need, I won't be far away.

KWONG: Listen - OK, this audio may make you cringe. It may make you cry. But you're going to feel something because shedding emotional tears is a very Homo sapien thing to do. Don't run away from it because it appears we're the only species to cry because of our feelings.


LIZZO: (Singing) I'm crying 'cause I love you.

KWONG: And I wanted to know why. It's a deep, deep well of research that we're going to explore today.

SCOTT: Today's episode is inspired by that eternal question from Lizzo.


LIZZO: (Rapping) What the [expletive] are [expletive] feelings, yo?

KWONG: Hearing this, we wondered the same thing.

SCOTT: From glistening eyeballs to full-on waterworks, what are tears for anyway? I'm Aaron Scott.

KWONG: And I'm Emily Kwong, and this is SHORT WAVE, the podcast where we like to tell stories and cry.


SCOTT: So, Emily, let us start with tears themselves. What are they?

KWONG: Well, there are actually three different kinds of tears, but scientists were kind of slow to figure that out. The father of evolution, Charles Darwin, dismissed tears entirely. He thought they were a side effect of facial muscle contractions, like we were squeezing them out of our face, and totally useless for survival.

SCOTT: Oh, dear. Spoken like a true stereotypical Victorian man - so well-dressed, yet so bad at expressing themselves.

KWONG: Yeah. Stiff collars will do that to you. One of the first people to say anything scientific about tears was Niels Stensen, a Danish scientist with a peculiar past.


UNIDENTIFIED PERSON: He was a sickly kid whose school chums died of plague. He survived to cut up corpses as an anatomist studying organs shared across species.

SCOTT: Oh, wow.

KWONG: Yeah. This is audio from a TED-Ed video about him. And all this organ cutting up did lead to a major revelation. So in 1662, Stensen figured out that what we now call our basal tears - that's one of the three kinds - come from the lacrimal gland. I'm going to explain how it works. This little squishy organ, the lacrimal gland inside your face, is right above the outer corner of both eyes, and it's consistently secreting a fluid made from salt and water. And when you blink, this fluid mixes with mucus and oil from another gland right along the edge of your eyelashes, and it spreads the moisture evenly across the surface of your cornea. This mixture then drains through your tear ducts and into your nose, keeping your eyes clean and moist around the clock. Now, unfortunately, Stensen was wrong in thinking that moisture was the sole purpose of tears.

SCOTT: Yeah, I was going to say. That doesn't allow for things like the tears that spring up when I cut an onion.

KWONG: Yeah, that's the second kind of tears, irritant tears. Those happen when something nasty in our environment - like smoke or skunk musk or, yes, the alliinase in onion - gets too close and we produce big gobs of irritant tears to protect our eyes in far greater quantities than basal tears to wash the irritant away and fight germs.

SCOTT: So tears are medicinal. I love that.

KWONG: Yeah, tears actually contain an antibacterial enzyme called lysozyme, which breaks down organisms that get in our eyes. But for the rest of the episode, I want to focus on the third kind of tears - emotional tears, tears from a psychological event. Randolph Cornelius is a professor of psychological science at Vassar College, and he's been studying emotional tears since 1979. And he confirms there's not one emotion that produces tears.

RANDOLPH CORNELIUS: There's the whole sadness family. There's nostalgia. There's happiness. There's anger. There's irritation, regret. Those can all be associated with tears.

SCOTT: Right, right, right, right. There's a song, actually, Emily, that illustrates this for me. You had Lizzo. I want to bring in "Long Ride Home" by Patty Griffin.


PATTY GRIFFIN: (Singing) Someone dug a hole 6 long feet in the ground. I said goodbye to you.

SCOTT: This song is about a person driving home from the funeral of their partner of 40 years, and I first heard it when there were several deaths in my life. It always fills me with such intense loss for the people that you build relationships with and you share experiences with. And it's beautiful, those memories, but it's also just so, so full of sadness.


GRIFFIN: (Singing) ...Ride home.

KWONG: And those tears that fall from something like that, Aaron - they come from a really unique place in our bodies.

SCOTT: Where is that?

KWONG: They come from the limbic system, the parts of our brain that have to do with our feelings. So when you feel an intense emotion - say, hurt during a breakup or joy during a wedding - you get worked up. Your heart rate may go up. Your breathing changes. And that response comes from the sympathetic nervous system - think fight or flight. Basically, your body is getting riled up. But when you cry, your body actually starts to relax. Your heart rate slows down. And the opposite system, the parasympathetic nervous system, is getting involved, which suggests that tears are something that actually may allow our nervous system to mellow out and recalibrate.

SCOTT: Which is very similar, I think, to what you learned about laughter, right?

KWONG: Maybe, yeah. Scientists aren't really sure. One idea introduced by psychologists at Temple University is a two-stage theory of tears, that there's this swell of emotion, and then (imitating crying) the crying is the comedown. But keep in mind, we still don't really know in detail the neurobiology of how this all works.

SCOTT: Right, right, right. And it can't just be biology either. I mean, I wonder about nature versus nurture here because it seems like why we cry is totally impacted by our culture, by our family upbringing, by our own personal psychology. I mean, have researchers looked into how crying, you know, like, figures into who we are as social creatures?

KWONG: They have. And this is the other side of it. How does our crying influence others? Randy pointed out to me - and I didn't realize this - when babies are born, they don't actually shed tears right away.


CORNELIUS: They shut their eyes really hard and scream. I've got three grandchildren, so I can tell you, yes, this happens.

KWONG: Emotional tears don't flow until babies are a few weeks old. Instead, they're just this red-faced, scrunchy, fit fest. A lot of mammals do this. They make a distress call. And according to Ad Vingerhoets at Tilburg University in the Netherlands, who has led so much of this research on adult crying, this expression of helplessness may be the evolutionary basis of emotional crying. It's about how others react to us. And what may have gone down is that our ancestors' distress calls simultaneously stimulated the release of tears. And somewhere in evolutionary time, this convergence of tears with crying out proved to be super helpful for survival.

SCOTT: How so?

KWONG: Well, when a baby cries, what do you do?

SCOTT: You try to help them.

KWONG: And when an adult cries, what do you do?

SCOTT: You put your arm around the person and tell them it's going to be OK.

KWONG: Right. And there's an added advantage to tears over crying. Vingerhoets, in his TEDx Talk makes the point that tears are silent.


AD VINGERHOETS: The great advantage of silent tears is that this specific call for help can be aimed at the individual without showing one's weakness to others, including possible predators.

SCOTT: OK, that makes sense.

KWONG: Right? Crying gets us the support we need, which is why Vingerhoets and others theorize it persists so far into adulthood. They call adult tears social glue. Here's Randy again.

CORNELIUS: I can tell you scenarios of being in hospitals where people are crying, and all you want to do is go over and hug them and, you know, comfort them. So tears, in my view, evolved as a signal to others to provide us with social support.

SCOTT: Interesting. Makes sense. And yet, if crying is this powerful social connector, why does it so often happen when we're alone?

KWONG: Yeah. It's weird, right? So the reason that you may be holding back your tears could be social, too. Because Randy says, in those moments, you may decide that the social cost of letting your tears flow is too high.

CORNELIUS: We know that there are situations in which we don't want to appear to be vulnerable. We don't want to appear to be in need, and so we'll hide our tears or wipe them away. And I'm sure you've seen this, you know, with men at a sad movie or something, they start to cry, holding their hands over their eyes so that no one can see them cry.

KWONG: Yeah. So it's almost like we're hijacking our evolutionary response in those moments. This may not surprise you, Randy says the majority of studies looking at tears in a lab setting have focused on adult women. There's less research on the tears of men and people of other genders. And when it comes to kids, they actually cry the same amount until early adolescence, and then gender differences start to appear. And there's been very few studies as to why.

SCOTT: Yeah, I'm going to blame this one on the American idea that there's no crying in baseball.

KWONG: Truly. And it makes a researcher like Randy all the more special, someone who not only studies tears, but is really willing to talk about emotions. As our interview wound down - we were on the phone - he started talking about the light outside his office window that was filtering through. The sun was setting. And he said to me, you know, it makes me think about these past 40 years of researching tears and how it's all winding down.

CORNELIUS: And tonight, you know, the leaves on the trees are amplifying that light. And I can see myself sitting here alone in the office thinking about my imminent retirement, the thousands of students I have taught. I'm sure I would tear up, you know? It's just the day for it, just the time for it. I may burst into tears after we hang up.

KWONG: Well, I welcome them.

CORNELIUS: Yes, tears are to be welcomed.


SCOTT: Emily, thank you for welcoming a little science into our tears and helping us understand why we cry a little more deeply.

KWONG: Yes. I maintain they're ultimately a mystery, maybe even slightly beyond the reach of science. Thanks, Aaron. The audio you heard it from Ad Vingerhoets from his TEDx Talk, "Why Do Only Humans Weep," given at TEDx Amsterdam. You can see the full video on ted.com. And for more TED and audio, follow the TED Radio Hour with NPR wherever you're listening to this.

SCOTT: This episode was produced by Berly McCoy and Rebecca Ramirez, edited by Brit Hanson and fact-checked by Abe Levine. The audio engineer was Gilly Moon. Gisele Grayson is our senior supervising editor. Brendan Crump is our podcast coordinator. Our senior director of programming is Beth Donovan, and the senior vice president of programming is Anya Grundmann. I'm Aaron Scott.

KWONG: And I'm Emily Kwong. Thanks for listening to SHORT WAVE from NPR.


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