While many animals exhibit distress, shedding tears in response to emotional states appears to be a unique human trait. This article explores the distinctions in tear production and emotional expression across the animal kingdom.
The Distinctiveness of Human Emotional Crying
Human emotional crying, or psychogenic lacrimation, is a complex phenomenon. These tears are triggered by intense feelings like sadness, joy, or relief. Unlike other tears, emotional tears contain higher concentrations of protein-based hormones, such as prolactin, adrenocorticotropic hormone, and leu-enkephalin (a natural painkiller). This unique chemical composition suggests a link to the body’s stress response and emotional regulation.
The physiological process involves the lacrimal glands, located above each eye, which produce the tear fluid. A neuronal connection exists between these glands and the brain regions responsible for emotion, particularly the limbic system. Beyond physiological components, human emotional crying serves significant social functions. It acts as a powerful nonverbal signal of vulnerability, eliciting empathy, care, and prosocial behavior. Tears can also help individuals feel better after crying, especially with social support. This distinct form of crying sets human emotional expression apart from other species.
Tears Across the Animal Kingdom
Many animals across various species, including mammals, birds, and reptiles, produce tears. However, these tears serve primarily physiological rather than emotional purposes. The two main types of non-emotional tears are basal tears, which lubricate and nourish the eye, and reflex tears, produced to flush out irritants like dust, smoke, or strong fumes.
The common phrase “crocodile tears” refers to crocodiles appearing to cry while eating. This phenomenon is not linked to emotion but is a purely physical reaction, where jaw movements during feeding stimulate tear glands. Scientists have found that the chemical composition and electrolyte concentrations of tears are similar across many species. Despite anecdotal accounts, there is no scientific evidence to suggest that animals shed tears due to emotional states in the same way humans do.
How Animals Communicate Distress
While animals do not shed emotional tears, they communicate distress, pain, or other strong emotions in diverse ways. Vocalizations are common, with many species using whimpers, howls, or barks to signal discomfort or fear. A dog, for instance, might whimper when in pain or anxious.
Body language also plays a significant role in animal emotional expression. Animals may exhibit specific postures, such as cowering, tucking their tail, or trembling, to convey fear or submission. Pacing, increased urination, excessive licking or chewing, and changes in ear position or pupil dilation can also indicate stress. These behaviors, while clearly indicating an emotional state, do not involve the production of tears. The absence of emotional tearing in animals highlights a fundamental difference in how species express and process their internal states.
The Evolutionary Puzzle of Human Tears
The evolution of emotional crying in humans remains an area of scientific inquiry, with several theories attempting to explain its unique development. One prominent idea suggests that emotional tears evolved from the distress vocalizations seen in many young mammals. As human infants are born particularly helpless, crying serves as a powerful signal to elicit care and assistance from caregivers.
Another theory emphasizes the social bonding aspect, proposing that emotional tears act as a visual signal of vulnerability and a plea for support, fostering prosocial behaviors in others. The act of crying can also serve as a physiological release mechanism, helping to relieve stress and restore emotional balance, possibly by expelling stress-related hormones. While the exact evolutionary pathway is still debated, the social and communicative functions of emotional tears are widely considered central to their development in humans.