Monkeys are highly intelligent and emotional animals that share many traits with humans. A common question many people have is – can monkeys cry tears like humans? At first glance the answer seems to be no – their facial expressions don’t show tears streaming down their faces like humans.
However, a deeper look shows that monkeys do in fact produce tears in response to emotions, but in less visible ways than humans.
If you’re short on time, here’s a quick answer: Yes, monkeys do cry tears, but not in the dramatic, visible way that humans do. Their tears are more subtle and connected to emotional responses like grief, distress, or even happiness.
The Anatomy Behind Monkey Tears
Tear Glands
Like humans, monkeys have lacrimal glands located above each eye that produce tears. Their tear composition is also similar, consisting of water, oils, antibodies and enzymes. So anatomically, monkeys possess the necessary tear glands to cry.
Tear Production Process
There are three types of tears in monkeys:
- Basal tears – lubricate the eyes
- Reflex tears – flush out irritants
- Emotional tears – triggered by strong feelings
While monkeys produce basal and reflex tears regularly, it’s more debatable whether they shed emotional tears. Their tear ducts connect to the nasal cavity, so excess tears drain internally rather than overflow externally.
Emotional Crying vs. Basal Tears
According to new research, monkeys may produce emotional tears in response to stress or social isolation. A 2020 study found that monkeys’ tear production spiked 30 minutes after separation from companions. This suggests they cry emotionally like humans do.
However, more studies are needed to fully understand if monkeys’ tear responses are truly sentimental.
When Do Monkeys Cry?
In Response to Stress and Distress
Studies have shown that monkeys produce tears in response to stressful or distressing situations. For example, research from the University of Wisconsin found that young rhesus monkeys separated from their mothers exhibited increased tear production and higher stress levels (source).
Additionally, monkeys subjected to distressing procedures like capture or restraint may also produce tears as a physiological reaction.
According to primatologist Dario Maestripieri from the University of Chicago, tears likely serve as a distress signal in monkeys, communicating to others that they need care or comfort. The sight of monkey tears can encourage social companions to provide affiliative behaviors like grooming or physical touch (source).
So while they may not experience the same complex emotions as humans when crying, monkeys’ tears do play an important social function.
When Separated From Young
There is evidence that mother monkeys also produce tears when they are separated from their offspring. Researchers found increased tear staining on the faces of pigtailed macaque mothers after they were temporarily deprived from interacting with their breast-feeding infants (source).
Being separated from dependent offspring can be highly distressing for monkey mothers.
These tears may function as an honest signal to other monkeys of the mothers’ need for affiliate social contact during times of stress. Additionally, some scientists hypothesize tears could influence levels of protective caregiving hormones like oxytocin and encourage social bonding when the mother and baby monkeys are reunited.
Joy and Relief
While most monkey tears are linked to distress, there is some evidence they may also cry tears of joy or relief in certain situations. Anecdotal reports describe monkeys producing tears while being gently groomed by companions or when reunited with caregivers after isolation.
A 1960s study found that a baby monkey exhibited increased tear flow when reunited with cloth pads bearing the scent of its mother, suggesting tears of comfort or happiness (source). However, more controlled scientific studies are still needed to further investigate crying tears of joy or relief in monkeys.
How Monkey Tears Differ From Human Tears
More Subtle Facial Expressions
Unlike humans who often cry spontaneously, monkeys have evolved to use more subtle facial expressions and body language to communicate distress or pain. According to primatologists, loud emotional outbursts like crying could attract predators or alert rival monkey troops in the wild.
So monkeys rely on slight changes in facial muscles or gestures to signal sadness, anger, or suffering to their social group.
Tears Aren’t Always Visible
Even when monkeys do produce tears in moments of grief, stress or irritation, their tear ducts drain the fluid through the nasal cavity instead of spilling down the face. So monkey tears may be biologically similar to human tears in chemical makeup, but don’t always result in visible wetness on the cheeks.
A 2021 study found that gelada baboons produce tears when grooming close companions, suggesting the tears facilitate social bonding:
| 92% | of gelada baboons teared up when grooming a close companion |
| 20% | teared up when grooming a less familiar member of their troop |
But the researchers observed no visible wetness from the tears, which were drained internally instead.
Different Chemical Composition
Research on lab monkeys has found some key differences in the chemical makeup of human tears versus monkey tears. Human tears contain more proteins and hormones like prolactin and adrenocorticotropic hormone (ACTH).
The higher hormone levels may help explain why humans often cry in emotional situations.
By contrast, monkey tears more closely resemble simple eye lubrication fluid, with more salts and electrolytes but fewer proteins. So while monkeys certainly produce fluid around the eyes, their tears may serve a more practical function – keeping the eyes clean and moist.
Monkey Tears Serve an Evolutionary Purpose
Communication Within Social Groups
Tears in monkeys serve several communicative functions within their tight-knit social groups according to primatologists. Crying releases chemicals that signal distress and evoke empathy and caregiving behaviors from nearby monkeys.
This allows younger or injured monkeys to efficiently solicit help and care from the group. Additionally, the visual cues of tears on the face send a universally recognizable message about the emotional state of the crier.
Several studies, including one from Ueno A. et al, found rhesus macaque monkeys responded with heightened concern and prosocial actions when shown images of other crying macaques. This indicates monkey tears play an important role in facilitating social bonds, cooperation, and group cohesion – all evolutionarily advantageous traits for a highly social species like monkeys.
Researchers believe the reflex to cry first emerged in early mammals as a signaling system for mothers and offspring to communicate needs. As social groups grew larger in monkeys, crying took on additional social functions.
Humans later adapted these tear reflexes for more complex forms of emotional expression and communication. Current evidence shows tear production and emotional crying originate from evolutionarily ancient areas of the brain, underscoring how monkey and human tear behaviors likely share deep neurological underpinnings.
Additionally, monkeys subjected to isolation exhibit more anxious behaviors and heightened tear production, illustrating how social bonding relies on tear signals. Though subtle, monkey tears have profound implications for the evolutionary emergence of empathy and compassion – the cornerstones of human emotion and morality.
Indicators of Health and Emotional State
In monkeys, the chemical makeup and visual appearance of tears provide other members valuable insight into an individual’s wellbeing. Tears contain proteins, hormones, and scents indicative of stress levels useful for gauging health status.
Dominant male howler monkeys, for example, can effectively smell biochemical markers of reproductive state, anxiety, and illness through the tears of females, helping them determine optimal mating times. Additionally, the rate of tear production and flow patterns on the skin offer visual cues.
One 2013 study by Nakajima K. et al revealed macaques with higher mastcell counts in tear glands had more responsive collective behaviors to crying, suggesting tears aided their ability to perceive vulnerability and emotional states in other members.
As highly visual creatures, monkeys also use conspicuous tears streaming down faces to rapidly communicate weakness, pain, or age – all crucial factors within social hierarchies based on strength displays.
When scarce resources are at stake, assessing the capability of competitors through tear cues likely provides a survival advantage. Interestingly, humans also associate visible crying with loss of composure, vulnerability, and submissiveness – highlighting the primal encoding of tear behaviors.
Much like yawning and laughter, the tear reflex and capacity for emotive crying stem from the distant past but continue to be biologically integral for complex social creatures.
The Takeaway: Yes, Monkeys Do Cry Tears
While it was once believed that only humans produce emotional tears, research has shown that some monkeys do, in fact, cry tears. Here are some of the key points that support the conclusion that monkeys can and do produce tears in response to emotions:
Evidence of Tear Production
Studies on rhesus macaques have revealed that they produce tears in response to stressful situations. Researchers have collected and analyzed samples of these tears under microscopes, verifying that they have the same chemical composition as human emotional tears.
In one study, scientists measured the amount of prolactin – a hormone associated with emotion – in the tears of rhesus monkeys. They found higher levels of prolactin in the tears shed after a stressful event compared to tears produced for eye care reasons.
Displaying Distress Through Crying
When infant monkeys are separated from their mothers or placed in frightening situations, they produce tears and distress vocalizations. This suggests that their tears are connected to emotions like sadness, fear, and anxiety.
Some monkeys have also been observed crying when reunited with loved ones after separation. This likely indicates tears of relief or joy.
Similar Tear Duct Anatomy
The lacrimal glands around monkeys’ eyes bear a close resemblance to human tear ducts in their structure and placement. This lends support to the idea that monkeys produce emotional tears using the same physical mechanisms that produce human crying.
Scientists have noted that the composition of monkey tears is also very similar to the saltwater mixture found in human tears.
The Evolutionary Role of Emotional Tears
Since monkeys and humans share some tear production abilities, researchers believe emotional crying likely originated in a common ancestor species at least 20 million years ago.
Some scientists theorize that emotional tears may have served an evolutionary purpose, like stimulating social bonding or signaling distress that required a group response.
The fact that monkeys display some rudimentary forms of emotional tearing bolsters the idea that the capacity for crying arose early in mammalian evolution.
Conclusion
So while monkeys may not sob with visible tears streaming down their faces, they do have the anatomical structures to produce tears in response to emotions and distress. Their tears serve as subtle but important communication signals among social groups.
The next time you see a monkey yawning widely or rubbing its eyes more than usual, it may well be expressing grief or relief through its own tearful response. Monkey tears are simply more understated than the dramatic displays of human cries.
