section_path: Behavior/Communication
section_name: Communication
paragraph_text: Communication
  
  Lemurs, lorises, tarsiers, and New World monkeys rely on olfactory signals for many aspects of social and reproductive behavior. Specialized glands are used to mark territories with pheromones, which are detected by the vomeronasal organ; this process forms a large part of the communication behavior of these primates. In Old World monkeys and apes this ability is mostly vestigial, having regressed as trichromatic eyes evolved to become the main sensory organ. Primates also use vocalizations, gestures, and facial expressions to convey psychological state. Facial musculature is very developed in primates, particularly in monkeys and apes, allowing for complex facial communication. Like humans, chimpanzees can distinguish the faces of familiar and unfamiliar individuals. Hand and arm gestures are also important forms of communication for great apes and a single gesture can have multiple functions.
  
  Primates are a particularly vocal group of mammals. Indris and black-and-white ruffed lemurs make distinctive, loud songs and choruses which maintain territories and act as alarm calls. The Philippine tarsier, has a high-frequency limit of auditory sensitivity of approximately 91 kHz with a dominant frequency of 70 kHz, among the highest recorded for any terrestrial mammal. For Philippine tarsiers, these ultrasonic vocalizations might represent a private channel of communication that subverts detection by predators, prey and competitors, enhances energetic efficiency, or improves detection against low-frequency background noise. Male howler monkeys are among the loudest land mammals as their roars can be heard up to 4.8 km (3.0 mi), and relate to intergroup spacing, territorial protection and possibly mate-guarding. Roars are produced by a modified larynx and enlarged hyoid bone which contains an air sac. The vervet monkey gives a distinct alarm call for each of at least four different predators, and the reactions of other monkeys vary according to the call. Furthermore, many primate species including chimpanzees, campbell's mona monkeys or diana monkeys have been shown to combine vocalizations in sequences, suggesting syntax may not be uniquely humans as previously thought but rather evolutionary ancient, and its origins may be deeply rooted in the primate lineage. Male and female siamangs both possess inflatable pouches in the throat with which pair -bonds use to sing "duets" to each other.
  
  Many non-human primates have the vocal anatomy to produce human speech but lack the proper brain wiring. Vowel-like vocal patterns have been recorded in baboons which has implications for the origin of speech in humans. Consonant- and vowel-like sounds exist in some orangutan calls and they maintain their meaning over great distances. The time range for the evolution of human language and/or its anatomical prerequisites extends, at least in principle, from the phylogenetic divergence of Homo (2.3 to 2.4 million years ago) from Pan (5 to 6 million years ago) to the emergence of full behavioral modernity some 50,000–150,000 years ago. Few dispute that Australopithecus probably lacked vocal communication significantly more sophisticated than that of great apes in general.