Crying is an important emotional expression and biological function found in many animals, but not all. While humans cry tears in response to emotions, animals may cry for other reasons. However, some animals lack the anatomical structures necessary for producing tears and cannot cry at all.
Mammals That Cannot Cry
Most mammals have the ability to produce tears for lubricating and protecting the eyes. However, there are a few exceptions:
- Snakes – Snakes lack eyelids and tear ducts, so they do not produce tears.
- Birds – Birds’ eyes do not water like mammals. They have a third eyelid called a nictitating membrane that functions to clean and lubricate their eyes.
- Fish – Fish live underwater, so their eyes do not require tears to stay moist. Their eyes are lubricated by the surrounding water.
- Insects – Insects do not have lacrimal glands to produce tears. They also lack eyelids to spread tears over their eyes.
- Spiders – Spiders also lack tear glands and do not cry.
While these animals do not cry tears, some may still make crying-like vocalizations to communicate, such as distress calls. But biologically, they are incapable of shedding emotionally-driven tears from tear ducts.
Why Do Humans Cry?
Humans cry for many emotional and physiological reasons. Some key reasons we shed tears include:
- Physical pain
- Empathy for others’ emotions
- When yawning or laughing hard
Crying is believed to be an outlet for intense emotions. Tears released contain stress hormones and other substances that build up during emotional events. Neuroscientists believe crying may help the body return to a calm, balanced state after being upset.
The Biological Process of Human Tears
Human tears emerge through the lacrimal system:
- Lacrimal glands near the eyes produce a saline fluid containing water, oils, and other substances.
- The lacrimal fluid flows through ducts to the surface of the eyes.
- Small openings called puncta drain any excess fluid into the nasal cavity.
- When crying, excess lacrimal fluid spills out through the tear ducts, flowing down the cheeks as tears.
Interestingly, emotional tears contain different biochemical makeup than tears shed for eye irritation. Emotional tears contain more protein-based hormones, which researchers believe contribute to mood regulation.
Why Can Some Animals Cry?
Any animals with lacrimal glands and tear ducts may potentially cry emotionally. But which animals shed tears in response to feelings?
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Research shows that animals like dogs, elephants, apes, and possibly cows and horses may produce tears in response to emotions like grief, joy or distress. They have been observed crying under stressful conditions, such as separation from their families. However, more research is needed to confirm the emotional nature of animal tears compared to reflexive tearing.
Why Do Dogs Cry?
Dogs definitely cry tears when stressed or upset. Tears may stream down a dog’s face when it is grieving the loss of a family member or is separated from its owner. A dog may also cry tears of joy when reunited with a beloved human after a long absence. But dogs do not shed tears as freely as humans do.
Do Cats Cry?
Cats do not appear to cry emotional tears. They produce tears to lubricate their eyes and remove irritants like dust. But cats likely do not associate their eye watering with emotions or communications. Though cats can feel emotions like sadness and grief, they may express them through behaviors other than crying, such as withdrawal or attention-seeking actions. More research on cats’ lacrimal systems is needed.
In summary, the ability to produce emotional tears is rare in the animal kingdom. Only a handful of animals, including dogs, elephants and apes have been observed crying in response to feelings like sadness, joy or distress. Most other mammals and animals produce reflexive tears solely for eye health rather than emotional expression. Humans are unique in crying frequently for emotional reasons due to our advanced lacrimal system and neurological wiring. But those animals that do shed emotional tears provide a glimpse into the evolutionary origins of crying as a communication signal and mood regulator.