Big ideas.
Once a week.
Subscribe to our weekly newsletter.
The Science of Tears: Why Do Humans Cry?
Crying depends on your culture, gender, attachment style, and so many other factors.

My mom, sisters, and many female friends are addicted to the show This is Us. When it’s about to air one of them usually posts something to their social media like, “Better get the tissues ready.” Of course, I myself avoid the show like a plague ravaged raccoon. But it got me thinking about this sadness-induced physical response. We can cry out of sadness, fear, frustration, anger, or even joy. But why do streams of liquid leave our eyes?
The truth is no one really knows for sure. That is to say, scientists don’t agree why tears stream down our cheeks and we’re wracked with spasms, and of course the telltale wailing and sobbing that comprise having a full-blown cry. There’s also great variety among humans. We all have a different threshold for the act. Some of us never even cry at all.
In a scientific sense, we’re the only organisms who tear up due to our emotions. Other creatures do so merely to remove irritants from their eyes. Many psychologists believe that in addition to giving us an outlet for a rapid buildup of a powerful emotions, crying is a social signal to others that we’re in distress. Care-taking at times of great stress can increase the bonds between individuals in a group, making them more in tune with one another, better able to communicate and understand each other, increasing teamwork among them and so their likelihood of survival.
Crying may be a social cue for support, which can in turn lead to more social cohesion. Getty Images.
Children and infants cry to get the attention of parents and have their needs met. Biochemist William H. Frey, PhD in the 1980s studied crying and tears. He found that on average, women cry 5.3 times a month, while men cry 1.3 times in that same time period.
There may be a biological reason behind this. The hormone prolactin is thought to promote crying. This is found at higher levels in women. While testosterone may dampen the act. Crying is different in different cultures as well.
In a 2011 study published in the journal Cross-Cultural Research, investigators looked at 35 different countries to see how often women cried. Richer countries such as the US, Sweden, and Chile saw slightly higher rates of female crying, over poorer ones such as Nepal, Ghana, and Nigeria. Researchers believe it’s because there’s greater freedom of expression in developed countries.
One’s attachment style also plays a role. Dismissive attachment styles, those people who avoid or distrust intimacy, are the most likely to try not to cry, or fight back tears. Those with insecure attachment, the needy, may cry inappropriately, such as going into histrionics in order to receive attention. While those with secure attachment style are the most likely to cry appropriately and naturally.
Women cry more often than men, and women from richer countries more often than poorer ones. Getty Images.
Some studies have looked into how children and others use tears as a form of manipulation. A child may cry in the presence of an angry mother to induce sympathy and try to get out of trouble. This could also be one reason why crying is often part of lovers' spats. A small study found that female tears can actually lower male sex drive and temper male aggression.
Another interesting find is that tears formed from different emotions actually contain different chemical makeups. Emotional tears contain more protein which is thought to make them thicker and so more likely to slip down slowly, causing streaks down the cheeks, which are easily noticed by others. It’s a call for support and empathy. Along those same lines, artist Rose-Lynn Fisher took tears shed from different emotions and photographed them under a microscope. The results are fascinating though not wholly scientific.
Meanwhile, scientists are turning their lenses on to those who don’t cry. Though we’re often think a good cry is a healthy catharsis, there’s actually no evidence to back this up. Some psychologists however, believe that bottling up such emotions might lead to feelings of anger later on while some scientists see crying as a way to shed the hormone cortisol from the body, ejecting it with the tears themselves.
To learn more about the science behind crying, watch this:
Weird science shows unseemly way beetles escape after being eaten
Certain water beetles can escape from frogs after being consumed.
R. attenuata escaping from a black-spotted pond frog.
- A Japanese scientist shows that some beetles can wiggle out of frog's butts after being eaten whole.
- The research suggests the beetle can get out in as little as 7 minutes.
- Most of the beetles swallowed in the experiment survived with no complications after being excreted.
In what is perhaps one of the weirdest experiments ever that comes from the category of "why did anyone need to know this?" scientists have proven that the Regimbartia attenuata beetle can climb out of a frog's butt after being eaten.
The research was carried out by Kobe University ecologist Shinji Sugiura. His team found that the majority of beetles swallowed by black-spotted pond frogs (Pelophylax nigromaculatus) used in their experiment managed to escape about 6 hours after and were perfectly fine.
"Here, I report active escape of the aquatic beetle R. attenuata from the vents of five frog species via the digestive tract," writes Sugiura in a new paper, adding "although adult beetles were easily eaten by frogs, 90 percent of swallowed beetles were excreted within six hours after being eaten and, surprisingly, were still alive."
One bug even got out in as little as 7 minutes.
Sugiura also tried putting wax on the legs of some of the beetles, preventing them from moving. These ones were not able to make it out alive, taking from 38 to 150 hours to be digested.
Naturally, as anyone would upon encountering such a story, you're wondering where's the video. Thankfully, the scientists recorded the proceedings:
The Regimbartia attenuata beetle can be found in the tropics, especially as pests in fish hatcheries. It's not the only kind of creature that can survive being swallowed. A recent study showed that snake eels are able to burrow out of the stomachs of fish using their sharp tails, only to become stuck, die, and be mummified in the gut cavity. Scientists are calling the beetle's ability the first documented "active prey escape." Usually, such travelers through the digestive tract have particular adaptations that make it possible for them to withstand extreme pH and lack of oxygen. The researchers think the beetle's trick is in inducing the frog to open a so-called "vent" controlled by the sphincter muscle.
"Individuals were always excreted head first from the frog vent, suggesting that R. attenuata stimulates the hind gut, urging the frog to defecate," explains Sugiura.
For more information, check out the study published in Current Biology.
Moral and economic lessons from Mario Kart
The design of a classic video game yields insights on how to address global poverty.
Mario kart on giant screens
Poverty can be a self-sustaining cycle that might require an external influence to break it. A new paper published in Nature Sustainability and written by professor Andrew Bell of Boston University suggests that we could improve global anti-poverty and economic development systems by turning to an idea in a video game about a race car-driving Italian plumber.
A primer on Mario Kart
For those who have not played it, Mario Kart is a racing game starring Super Mario and other characters from the video game franchise that bears his name. Players race around tracks collecting power-ups that can directly help them, such as mushrooms that speed up their karts, or slow down other players, such as heat-seeking turtle shells that momentarily crash other karts.
The game is well known for having a mechanism known as "rubber-banding." Racers in the front of the pack get wimpy power-ups, like banana peels to slip up other karts, while those toward the back get stronger ones, like golden mushrooms that provide extra long speed boosts. The effect of this is that those in the back are pushed towards the center, and those in front don't get any boosts that would make catching them impossible.
If you're in last, you might get the help you need to make a last-minute break for the lead. If you're in first, you have to be on the lookout for these breakouts (and the ever-dreaded blue shells). The game remains competitive and fun.
Rubber-banding: A moral and economic lesson from Mario Kart
In the real world, we see rubber-banding used all the time. Welfare systems tend to provide more aid to those who need it than those who do not. Many of them are financed by progressive taxation, which is heavier on the well-off than the down-and-out. Some research suggests that these do work, as countries with lower levels of income inequality have higher social mobility levels.
It is a little more difficult to use rubber-banding in real life than in a video game, of course. While in the game, it is easy to decide who is doing well and who is not, things can be a little more muddled in reality. Furthermore, while those in a racing game are necessarily antagonistic to each other, real systems often strive to improve conditions for everybody or to reach common goals.
As Bell points out, rubber-banding can also be used to encourage sustainable, growth programs that help the poor other than welfare. They point out projects such as irrigation systems in Pakistan or Payments for Ecosystems Services (PES) schemes in Malawi, which utilize positive feedback loops to both provide aid to the poor and promote stable systems that benefit everyone.
Rubber-banding feedback loops in different systems. Mario Kart (a), irrigation systems in Pakistan (b), and PES operations in Malawi (c) are shown. Links between one better-off (blue) and one worse-off (red) individual are highlighted. Feedback in Mario Kart (a), designed to balance the racers, imprAndrew Bell/ Nature Sustainability
In the Malawi case, farmers were paid to practice conservation agriculture to reduce the amount of sediment from their farms flowing into a river. This immediately benefits hydroelectric producers and their customers but also provides real benefits to farmers in the long run as their soil doesn't erode. By providing an incentive to the farmers to conserve the soil, a virtuous cycle of conservation, soil improvement, and improved yields can begin.
While this loop differs from the rubber-banding in Mario, the game's approach can help illustrate the benefits of rubber-banding in achieving a more equitable world.
The task now, as Bell says in his paper, is to look at problems that exist and find out "what the golden mushroom might be."
A new warning to sign to predict volcanic eruptions?
Satellite imagery can help better predict volcanic eruptions by monitoring changes in surface temperature near volcanoes.
Volcano erupting lava, volcanic sky active rock night Ecuador landscape
- A recent study used data collected by NASA satellites to conduct a statistical analysis of surface temperatures near volcanoes that erupted from 2002 to 2019.
- The results showed that surface temperatures near volcanoes gradually increased in the months and years prior to eruptions.
- The method was able to detect potential eruptions that were not anticipated by other volcano monitoring methods, such as eruptions in Japan in 2014 and Chile in 2015.
How can modern technology help warn us of impending volcanic eruptions?
One promising answer may lie in satellite imagery. In a recent study published in Nature Geoscience, researchers used infrared data collected by NASA satellites to study the conditions near volcanoes in the months and years before they erupted.
The results revealed a pattern: Prior to eruptions, an unusually large amount of heat had been escaping through soil near volcanoes. This diffusion of subterranean heat — which is a byproduct of "large-scale thermal unrest" — could potentially represent a warning sign of future eruptions.
Conceptual model of large-scale thermal unrestCredit: Girona et al.
For the study, the researchers conducted a statistical analysis of changes in surface temperature near volcanoes, using data collected over 16.5 years by NASA's Terra and Aqua satellites. The results showed that eruptions tended to occur around the time when surface temperatures near the volcanoes peaked.
Eruptions were preceded by "subtle but significant long-term (years), large-scale (tens of square kilometres) increases in their radiant heat flux (up to ~1 °C in median radiant temperature)," the researchers wrote. After eruptions, surface temperatures reliably decreased, though the cool-down period took longer for bigger eruptions.
"Volcanoes can experience thermal unrest for several years before eruption," the researchers wrote. "This thermal unrest is dominated by a large-scale phenomenon operating over extensive areas of volcanic edifices, can be an early indicator of volcanic reactivation, can increase prior to different types of eruption and can be tracked through a statistical analysis of little-processed (that is, radiance or radiant temperature) satellite-based remote sensing data with high temporal resolution."
Temporal variations of target volcanoesCredit: Girona et al.
Although using satellites to monitor thermal unrest wouldn't enable scientists to make hyper-specific eruption predictions (like predicting the exact day), it could significantly improve prediction efforts. Seismologists and volcanologists currently use a range of techniques to forecast eruptions, including monitoring for gas emissions, ground deformation, and changes to nearby water channels, to name a few.
Still, none of these techniques have proven completely reliable, both because of the science and the practical barriers (e.g. funding) standing in the way of large-scale monitoring. In 2014, for example, Japan's Mount Ontake suddenly erupted, killing 63 people. It was the nation's deadliest eruption in nearly a century.
In the study, the researchers found that surface temperatures near Mount Ontake had been increasing in the two years prior to the eruption. To date, no other monitoring method has detected "well-defined" warning signs for the 2014 disaster, the researchers noted.
The researchers hope satellite-based infrared monitoring techniques, combined with existing methods, can improve prediction efforts for volcanic eruptions. Volcanic eruptions have killed about 2,000 people since 2000.
"Our findings can open new horizons to better constrain magma–hydrothermal interaction processes, especially when integrated with other datasets, allowing us to explore the thermal budget of volcanoes and anticipate eruptions that are very difficult to forecast through other geophysical/geochemical methods."
Stressed-out mothers are twice as likely to give birth to a girl
New research from the University of Granada found that stress could help determine sex.
