For humans, crying involves two distinct components: the physiological production of tears and the expression of a strong emotional state like sadness or grief. Scientists distinguish between physiological weeping, which serves a purely biological function, and emotional weeping, which is a complex psychosocial response. While most animals exhibit clear behavioral and vocal signs of distress, sorrow, or fear, the unique combination of these emotional states with the physical act of shedding tears is largely considered a human trait. The distinction centers on whether an animal’s tears are a deliberate emotional signal or simply a byproduct of their body’s mechanics.
The Biological Function of Animal Tears
Tears are a common biological feature across many different animal species, but their purpose is primarily functional, not emotional. The lacrimal apparatus, or tear system, produces a fluid film that coats the eye to maintain health and clear vision.
The main functions of this fluid are to lubricate the ocular surface and provide a smooth optical surface for light refraction. Tears also serve as a protective barrier, flushing away environmental debris, dust, and foreign materials from the eye. Furthermore, they contain antimicrobial factors like lysozyme and lactoferrin, which defend against microbial infection. Therefore, when a dog’s eyes water, or a bird has fluid around its eyes, it is typically a reflex response to irritation, injury, or a health issue, rather than an expression of sadness.
Vocalizations and Behavioral Displays of Distress
These displays serve as the primary communicative equivalent to human emotional crying, signaling an internal state of distress to others. In many social species, these actions are critical for soliciting comfort or help from the group.
Domestic dogs, for instance, often exhibit clear behavioral changes following the loss of a companion, including decreased play, loss of appetite, increased sleeping, and a rise in attention-seeking behaviors. They may also search persistently for the missing individual or emit prolonged whining and whimpering sounds, which are vocalizations of distress. These actions are direct indications of a disruption to their social bond.
In the wild, elephants are renowned for their sophisticated grief rituals, showing strong behavioral reactions to the death of a family member. They have been observed attempting to rouse the deceased or guarding and revisiting the remains for extended periods. Primates, such as chimpanzees, also display profound mourning behaviors, with mothers sometimes carrying the bodies of their deceased infants for days or even weeks, exhibiting signs of prolonged distress and social withdrawal. Orcas have also been documented carrying their dead calves for weeks. These intense, sustained behaviors communicate strong internal states without the need for tear production.
Comparative Neurobiology and Emotional Crying
While animals experience emotions and exhibit complex distress vocalizations, the specific mechanism that links a strong emotional experience to the physical secretion of tears is specialized in humans. The neurological pathways for emotional crying involve structures in the limbic system, which manages emotion, and requires the activation of the parasympathetic nervous system to stimulate the lacrimal glands.
Animal studies on distress calls show that these vocalizations are regulated by neurochemical systems that include neuropeptides like oxytocin and vasopressin, which are associated with attachment behavior. Hormones like prolactin are also implicated in human emotional tear production, but the connection between these neurochemicals and the actual shedding of tears as an emotional signal seems to be a human specialization. The human capacity for emotional tears may have evolved from the ancient mammalian distress call, transforming a simple vocal signal into a more complex, visually communicative social cue.