The study of animal behavior is driven by the desire to understand if the internal lives of other species mirror our own. Historically, Western thought viewed animals as purely mechanistic, driven only by instinct and lacking true feeling. This perspective has been challenged by ethology and comparative psychology, which now recognize the potential for complex inner experiences in many non-human species. Modern scientific inquiry systematically investigates the presence of emotional states and consciousness in our closest relatives.
Physical Manifestations of Distress
The question of whether a gorilla cries usually compares them to human emotional crying, which involves the production of psychic tears (lacrimation driven by emotion). Gorillas do not weep tears when distressed; humans are the only known primate species to exhibit this specific physiological response. All mammals produce tears that are either basal (for lubricating the eye) or reflexive (in response to an irritant). When gorillas experience negative emotion, they exhibit distinct physical behaviors, including specific vocalizations, postural changes, and self-comforting actions.
Infants emit high-pitched, wailing vocalizations when separated from their mothers or in pain. When older group members experience distress, such as following a death, observed behaviors include prolonged silence, lip-trembling, and intense staring at the deceased body. These responses are physical manifestations of suffering, even without emotional tear production.
Defining Complex Primate Emotions
Ethologists interpret these distinct behaviors as evidence of complex emotional states, such as grief and mourning, challenging the notion that emotion is a uniquely human trait. When dominant silverbacks die, troop members may gather around the body for hours or days, touching, sniffing, and grooming the remains. A juvenile who loses its mother may carry the corpse for an extended period, attempting to elicit a response or suckle from the body.
These acts suggest deep emotional attachment and an awareness of loss in great apes. For example, a group of Grauer’s gorillas interacted with the body of an unknown conspecific, demonstrating a response to death that transcended familiar social bonds. Other behaviors, such as reconciliation after conflict and comforting a distressed individual, provide evidence of empathy and sympathetic concern. Ethologists document these behaviors, distinguishing between emotional contagion and more complex responses that indicate an awareness of another’s feelings.
The Biological Foundation of Feeling
The capacity for complex feeling in gorillas is rooted in shared evolutionary biology, as humans and gorillas share nearly 98% of their DNA. This genetic overlap extends to the neurobiological structures that process emotion, including the conserved limbic system found in all mammals. Key components like the amygdala, which processes fear and emotional memory, and the hippocampus, linked to memory and spatial navigation, are functionally present in great apes.
Gorillas and other great apes possess specialized Von Economo neurons in the anterior cingulate cortex, a brain region associated with social bonding and complex decision-making. These neurons are dense in humans and great apes, suggesting a shared neurological basis for advanced social emotions. The physiological stress response is also conserved, involving the release of cortisol during threatening situations or social conflict. Non-invasive studies show that bonding hormones, such as oxytocin, can modulate this stress response and promote social buffering, where a bond partner’s presence decreases cortisol levels.
The interaction between stress and bonding hormones suggests gorillas possess the neurochemical hardware for sophisticated emotional regulation, similar to humans. Oxytocin fosters social bonding and affiliation in primates, and its release during social interactions underscores the importance of group cohesion. Anatomical studies show that brain structures vary based on ecological needs; for instance, western gorillas have a larger hippocampus than mountain gorillas, likely due to their larger home ranges and reliance on spatial memory for foraging.
Objective Study of Sentience
To move beyond anecdotal evidence, researchers employ rigorous, quantifiable metrics to objectively study sentience and consciousness in great apes. This approach minimizes anthropomorphism, the tendency to attribute uniquely human emotions or motivations to animals. One famous method is the mirror self-recognition (MSR) test, which assesses self-awareness by marking an animal in a location it can only see using a mirror.
Gorillas often fail the MSR test, but this is thought to be due to their behavioral ecology, as prolonged direct eye contact with a reflection can be interpreted as an aggressive gesture. Scientists have developed alternative, non-visual tests to measure self-awareness, such as the body-as-barrier task. In this experiment, gorillas must realize their own body is physically blocking access to a reward, demonstrating a cognitive understanding of their physical presence. Other methods include cognitive bias testing, which measures an animal’s “mood” by observing how it interprets ambiguous cues. For example, an animal in a negative emotional state may show a pessimistic bias by being slower to approach an ambiguous cue that might lead to a reward. These objective measures provide a foundation for the scientific consensus that great apes possess a level of sentience and consciousness.