The Acoustical Umbilical Cord

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This episode was written & produced by Katy Daily.

Many animals, humans included, are natural-born criers. It’s the most basic form of communication from right when we come into the world. But us humans are unique: we keep on crying until the day we die. What was born as a survival mechanism, develops a deeper fundamental need as we grow older. In this episode, we discover the hard-wiring in our brains that reach across species, and how our tears into adulthood make us distinctively human. Featuring Dr. Susan Lingle, Behavioral Ecologist at the University of Winnipeg, and Dr. Ad Vingerhoets, Research Psychologist at the University of Tilburg.

Music used in this episode

Timing is Everything - Blake Ewing
Missing Pictures - Steven Gutheinz
Finally, The Sun - Dustin Lau
Surface - Blake Ewing
Lie Cheat Steal (Instrumental) - Andrew Judah
Building Thoughts - Dexter Britain
Sleeper - Riley 1964
Unremarkable - Dexter Britain

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View Transcript ▶︎

[sniffling winds up, like a child is about to burst into tears]

You’re listening to Twenty Thousand Hertz...The stories behind the world's most recognizable and interesting sounds. I'm Dallas Taylor.

[baby shrieks and heaves]

We’re all natural-born criers. It’s the most basic form of communication... from right when we come into the world.

That’s producer Katy Daily.

When we’re babies… we cry when we’re hungry… [baby wail, sound of sucking on bottle] and when we’re in pain… [toddler shriek]. It’s the easiest way to communicate that something’s wrong, and to get the help we need.

For many animals... it’s actually built into the parents’ brains to react immediately to the sound of their infant’s cries. The parent might even see or smell the infant in distress, but it’s that sound that kicks them into gear.

Crying has to be loud enough to attract the parent, which unfortunately means that it’s loud enough to attract predators as well. So most animals, when they’re old enough to fend for themselves, have evolved to grow out of crying entirely.

Not humans. We keep on crying for the rest of our lives. Now, it’s more likely to be because of a bad break-up than an empty stomach, as we go from crying for necessity to crying emotionally. But if we don’t need to signal for that critical help anymore, what’s the purpose of crying when we’re emotional?

First, let’s talk about our wiring.

Susan: An infant's cry triggers an immediate response by caregivers.

That’s Dr. Susan Lingle, a behavioural ecologist who has studied animal cries in the wild.

Susan: So this might mean moving to the infant to hold it, to feed it, or to rescue it from a predator.

Not only does this increase the chance of survival for the infant, but it also ensures the caregiver’s genetic fitness. Meaning: the ability to successfully pass on its genes to the next generation.

Lingle attributes this to a special caregiver sensitivity. If the caregiver hears what sounds like their offspring crying, they will be biologically driven to respond to it.

But this isn’t just limited to parents. The same might happen to someone who doesn’t even have a child.

Susan: Cries made by newborns of different species are remarkably similar. We tend to hear this slight plaintive "Rear rear" for many species.

I've heard a few people give me anecdote about how they were camping, they woke up at 2:00 in the morning and heard a baby, a human baby crying. They left their tent to track down the sound, only to find a beaver baby… so these sounds are remarkably similar.

But we recognize more than just the cries that sound like ours. We know when our cat wants to be let out [meow], and when our dog is hungry [dog whimper].

And sometimes, our pets understand us too.

Susan: The brain of a domestic dog responds to human vocalizations very much the same way as the dog brain responds to dog vocalizations.

Most of us would recognize this: a dog might perk up and come on over when they hear their owner crying.

Susan: We tend to view the animals having learned to respond to our vocalizations because of our close association with dogs. We have a shared history that seems to be over 30,000 years. Some biologists suggest that this mutual understanding is due to an ability that evolved over the shared history of domestication.

Maybe our dogs can only understand us this way because they’ve developed an almost human-like empathy. So does this mean that only our pets can understand when we cry?

Susan: Most of my lab's work has been with the behavior of two species of deer, which are white-tailed deer and mule deer. We started to work with distress vocalizations or cries made by deer fawns when coyotes attack them [fawn cry SFX]. We started to notice that the acoustic structure of the cries made by newborns of different species were remarkably similar.

So, we returned to the field to conduct what I called "cross-species playbacks."

[researcher over radio – fur seal cry]

What you’re hearing is a recording of a fur seal pup crying. It’s playing over a big speaker in the middle of a field. There’s a female deer nearby.

Susan: She immediately lifts her head. And she starts running at a full gallop [gallop SFX] until she gets to the speaker.

When we did these playback experiments, we found that deer mothers approached a speaker playing newborn cries from these different species as if they were approaching the speaker to rescue their own fawns.

[human baby cry is heard, deer gallops towards speaker]

And there she goes again, this time for a human baby.

[kitten cry is heard, deer gallops towards speaker]

And again.

Susan: It is not as though she really wants to be defending a kitten. But the sounds is so similar that she can mistake it for the cry of a fawn.

There's such survival value for to respond when she hears the sound that it probably outweighs the cost of responding to cries when it's not your own infant.

What Lingle’s team found was that if another mammal’s cry fell within a certain frequency range, the mother deer would respond as if it were her own fawn. So if her fawn’s cry is roughly 900 hertz [example], then the mother might recognize another animal’s cry anywhere from around 400 hertz [example] to around 1,300 hertz [example].

Even animals that sound way different to our ears, might sound close enough to a mother deer.

Susan: Where many species have a frequency modulation, that rises and falls, "Rare Rare." The bat that we used had simple descending frequency sound "Eer Eer" [example] and it sounded quite odd to our ear.

So in these cross-species experiments, we predicted that the female would approach the speaker only when the pitch of the cry fell within that same frequency range.

The cries of many species, naturally fall into the range in which a deer mother will respond. But some species have a cry with a very low pitch and other species have a cry with a very high pitch.

Lingle’s team took the cry of a newborn eland, which is an antelope found in Africa. The eland’s cry naturally falls lower than this frequency range for the mother deer.

Susan: So we ran a series of playback trials using the original eland calls [eland call SFX]. Females alerted to these calls but turning their head toward the speaker but they did not approach and they did even always stand up, if they had been sitting down. We ran a second series with the same calls but in this case, we manipulated the pitch so that it fell in the range to which deer typically respond to cries. So we raised the pitch from 170 hertz [example] up to an average of about 900 hertz [example]. We were able to use software to increase the frequency of the pitch without changing any other acoustic traits in the call.

[higher frequency eland call]

When the deer heard these sounds, they immediately lifted their heads and took off at full speed [galloping SFX] toward the speaker. So this result told us that the pitch of the call is very important and it must fall within a certain frequency range for females to respond. But perhaps more importantly, this result told us that cries made by newborns of different species are very similar except for the difference in the frequency of the pitch.

Now, this is just mind-blowing for me. This mother deer is hearing the sound of a human baby cry, or a bat cry, and just takes off running towards the sound. It’s like she’s thinking “this might be my baby, so I have to save it.”

So far, we can’t look into the brain of this wild deer to see why she responds like this. So it’s still hard to know for sure if our pet dog understands our cries because she’s developed some human-like empathy, or if it’s actually been hard-wired into her long before domestication.

But it does make you wonder: If we hear a kitten cry, do we respond out of empathy or instinct?

Susan: I would probably say that in humans, rather than suggesting that it's our empathy that makes us responsive to these sounds, instead, the response of humans and deer to newborn cries of different species may reflect a shared sensitivity that has been conserved across mammals and perhaps even across other species that have well-developed parental care.

So crying triggers this caregiver instinct, and is incredibly essential to our survival. But once we’ve grown up and can survive on our own, why do we still cry?

More on that in a moment.

[music out]


[music in]

We’re learning that crying is essential to our survival as a species from the very day we were born.

Ad: One needs to be aware that the human infant is among the most helpless creatures that exist.

My name is Ad Vingerhoets and I'm a psychology professor of Tilburg University in Tilburg, the Netherlands.

You can compare it with the offspring of other primates, which all can cling to the fur of their mothers, or for example, to ducklings, who can immediately follow their mother when they are out of the egg.

One may consider infant crying as a kind of acoustical umbilical cord. Meaning that it helps to maintain or to re-establish the contact with the mother.

Then, we grow up. After all of the dirty diapers [baby cry SFX], and bumped foreheads [baby squeal SFX], we eventually cut that acoustical umbilical cord. Back to Katy.

It’s not that we stop vocally crying entirely, it’s that we do it way less often, and much more quietly. It’s almost like our bodies are trying to keep us from making a sound.

Listen, for example, to this iconic scene from Interstellar. In it, Matthew McConaughey breaks down into tears while watching videos from his family back home.

[Interstellar cry scene]

If you can’t hear him crying, it’s because he’s barely making a sound. Tears are rolling down his face. There’s just almost no noise. That’s because, as you become an adult, you don’t need to make that sound anymore. It sounds like he is trying to keep the sound in, and hold the tears back.

And this trait is uniquely human.

While we have observed crying in some animals like camels and elephants, humans are the only species who we know for sure produce emotional tears.

But if we’ve grown out of the need to cry for survival, then what’s the point of weeping when we’re emotional?

As it turns out, we don’t 100% know. There are a lot of theories out there, ranging from reasonable to downright outrageous. The most popular theory is that crying removes some kind of toxins that build up when you’re stressed. And it does sound convincing. I mean, sometimes, after a good cry, people just feel better.

Ad: One could also argue that if such a mechanism would be responsible for feeling better, that raises the question whether an act as peeling onions and the associated shedding of tears [onion chopping, nose sniffles SFX] may also help us to feel better when we are feeling blue.

So, tears do form to protect our eyes when they’re irritated, but this still doesn’t explain why they appear when we’re upset.

If it’s not purely physical, then what is it?

Ad: Tearful crying was just a much safer way of communication, and it can also be directed rather exclusively to specific persons, of whom one might expect to receive consolation.

When we are exposed to crying individuals, we often tend to react with all kinds of positive reactions. We feel more connected with them, we feel more empathy, and we tend to react with providing help, support, and so on.

The general idea about the function of tears is that tears connect. They help us to connect with others.

So even as adults, crying’s purpose is still a form of communication. Instead of wailing for survival, we weep… to tell others we need their support.

This doesn’t mean that we have control over our tears. Convincing tears are notoriously hard for actors. But then we might spontaneously cry in front of our boss despite our best efforts to keep them in.

This might even explain why we cry when we’re alone.

Ad: If we experience an emotion with a certain intensity, then it might be that this emotion becomes connected with the production of tears.

We might just be so used to this that we let the tears out, even when no one’s around to see.

If we could turn our tears on and off with a switch, most of us probably would. In some cases, crying makes us feel vulnerable in ways that we’re not always OK with. It might make us feel embarrassed. Or uneasy. Like others will judge us. And that might even condition us to get tearful less often.

Ad: How others react to an individual's crying depends, on the display rules of a certain culture.

For example, crying when one has lost a significant other, it's a universally accepted reason to cry. However, the situation is very different when one has the feeling that the crier can be blamed him or herself for the situation he is in.

[A League of Their Own clip – “there’s no crying in baseball!”]

That could explain why we sometimes feel better when we cry, and sometimes we feel worse. It might depend on how others react to us that determines how we feel afterwards.

So Vinger-oots and his team tried to compare normal criers and a group of people who had stopped crying. Did the criers get some kind of release that the non-criers didn’t? Or did the non-criers feel more secure, and less judged by others?

Ad: They did demonstrate some remarkable differences, especially in their social functioning.

More precisely, the criers reported more empathy, and they felt stronger connected with others. They reportedly also received more emotional support.

This doesn’t just go for when we’re sad, or angry, or frustrated.

Ad: Humans also start to cry more when we are being moved. For example, when we see that bonds become closer. Witnessing acts of altruism, acts of self-sacrifice.

[CNN clip – woman talks about her rescuer]

It's okay to cry with this kind of situation, because it's a strong signal to others that we are good people. They can connect with us and they can collaborate with us.

Humans are not just described as social beings, but even as ultra-social beings. We experience empathy, so we have the capacity to understand how others feel.

[deaf woman hears for the first time]

What is very helpful to trust each other is if you have the feeling that you understand each other, and not just understand in a cognitive sense, but you know what others value.

[dog reunites with owner]

I think that crying is very important, because crying in some way might have stimulated the development of our empathic skills.


When we cry, we share our values and our vulnerability. It brings us closer to together. It allows us to understand more about each other and develop a deeper feeling of trust and responsibility. And to connect in a way that’s uniquely human.

Twenty Thousand Hertz is produced out of the studios of Defacto Sound, a sound design team dedicated to making television, film, and games sound incredible. Find out more at defacto sound dot com.

This episode was written and produced by Katy Daily...and me, Dallas Taylor. With help from Sam Schneble. It was sound designed and mixed by Nick Spradlin.

Thank you to our guests, Dr. Susan Lingle and Dr. Ad Vinger-oots. They are both digging deeper into the mysteries of human and cross-species crying, with new details emerging as we speak. Special thanks to CKXU 88.3FM Radio in Lethbridge Alberta, Canada for their help, and to Drs. Isabelle Charrier, Radim Kotrba, and Paul Faure for their recordings of fur seals, elands, and silver-haired bats.

The music in this episode was provided by Musicbed and we have an exclusive playlist you can check out at music dot 20k dot org. That playlist also includes the track you’re hearing right now “Unremarkable” by Dexter Britain.

As always, thanks for listening.

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