Smell, or olfaction, plays a crucial and multifaceted role as a signal among non-human primates, influencing various aspects of their social behavior, reproduction, and communication. Unlike humans, whose sense of smell is often considered less acute, many primate species rely heavily on chemical cues (pheromones) for information exchange.

One primary function of olfactory signals is in reproduction. Females often release specific pheromones when they are in estrus, signaling their reproductive readiness to males. Males, in turn, can detect these cues, which can influence their mating strategies, competition, and mate choice. For example, some prosimians and New World monkeys use urine-washing or scent-marking with glandular secretions to advertise their reproductive status or territorial claims.

Territorial marking is another significant use of smell. Primates deposit scent marks (from urine, feces, or specialized glands) on trees, branches, or other objects within their territory. These marks communicate presence, ownership, and sometimes even the identity of the individual or group, helping to avoid direct conflict with neighboring groups. The intensity and freshness of the scent can convey information about how recently the territory was marked.

Olfactory signals also contribute to social recognition and cohesion. Primates can recognize individuals, their social status, or even their emotional state through their unique scent profiles. Scent-marking can reinforce group identity and facilitate bonding. For instance, mutual grooming often involves sniffing, which can help maintain social bonds and identify group members.

Furthermore, smell can act as an alarm signal, though less commonly than visual or auditory cues. The scent of a predator or the stress hormones released by a frightened individual can alert others to potential danger. Overall, olfactory communication in non-human primates is a complex system that provides vital information about an individual's physiological state, social standing, and environmental context, underpinning their survival and social dynamics.