Primatology is the study of nonhuman primates (NHP) or, as sometimes identified, the alloprimates, meaning primates other than us. The order Primates includes the prosimians, Old and New World monkeys, apes, and humans. The study of humans is relegated to the social sciences (that is, anthropology, geography, psychology, and sociology) and, although humans are primates, the study of humans is not included as part of primatology. Primatology, in contrast, is generally viewed as part of the life sciences. Nonhuman primates have been studied by psychologists, zoologists, and biological anthropologists in both the laboratory and in their natural habitats. In general, biological anthropologists study NHP under semi-natural conditions or in their natural habitat.
Primates are eutherian (that is, placental) mammals having, for example, hair, mammary glands for nursing their offspring, a physiology for maintaining a constant body temperature, and different types of teeth identified as incisors, canines, premolars, and molars. The traits unique to primates include an increase in brain size and a lengthening of all stages of the life cycle, stereoscopic vision with the eyes encircled by bones, color vision, sensitive ridged pads with nails at the end of the digits instead of the typical mammalian claws, opposable digits, and hands and feet in place of paws. Primates also have a generalized skeleton and variable locomotor patterns and feeding postures.
The prosimians belong to the suborder Prosimii that includes the lemurs, sifakas, indris, and aye-ayes of Madagascar, the galagos of Africa, the loris of Africa and Asia, and the tarsier of Asia. Prosimians have more retained (that is, primitive mammal-like traits) than the other suborder of primates, the Anthropoidea. These retained traits of the prosimians include a rhinarium or wet-nose, some claws, eyes not completely enclosed in bone, smaller brain size, and less control of individual fingers than seen in the anthropoid primates. The anthropoid primates, the monkeys, apes, and humans, lack the wet-nose, and have eyes completely encased in bone, relatively large brains, and nails on all of their digits. Some primatologists, particularly those who study early primate evolution, prefer to divide the order Primates into two suborders designated as the Strepsirhini, the wet-nosed prosimians, and the dry-nosed Haplorhini, which includes the tarsier, New and Old World monkeys, apes, and humans.
Primatology began in the 1800s as mainly a study of primate anatomy and an attempt to understand where primates, including humans, fall within the classification system constructed by Linnaeus in the mid-1750s. The first attempts to send researchers into the field to observe NHP in their natural habitat was initiated in the early 1930s by psychologist Robert Yerkes who sent N. W. Nissen and H. C. Bingham to observe chimpanzee (Pan troglodytes) and gorillas (Gorilla gorilla), respectively. Another psychologist supported by Yerkes was Clarence R. Carpenter who studied howler monkeys (genus Alouatta) and spider monkeys (genus Ateles) on Barro Colorado Island in the Panama Canal and arranged for 500 Indian rhesus monkeys (Macaca mulatta) to be moved to Cayo Santiago, an island off the coast of Puerto Rico. Carpenter was also part of the 1937 Asian research project to study gibbons (genus Hylobates) initiated by Harold Coolidge, Jr. Sherwood L. Washburn, who would play a major role in the development of primatology following WWII, was also part of the Coolidge expedition.
Following the aftermath of World War II the study of alloprimates in their natural habitat began again. In the 1950s Japanese biologists started to study Japanese macaques (Macaca fuscata), but this work was not translated into English until 1957. The work of the Japanese primatologists is now accepted in the West, and Japanese primatologists publish in English language journals. In the late1950s, Irven DeVore, under Washburn, studied baboons (Papio anubis) in Kenya. Subsequently Washburn sent a series of University of California, Berkeley, graduate students, recruited from among those studying cultural anthropology, to observe a wide range of NHP. Washburn was mainly interested in what NHP might tell us about human evolution. Soon, however, anthropologists were studying NHP because the NHP are interesting for their own sake, and anthropologists have the best methods for studying the social lives of the alloprimates. Pioneering studies were conducted by Phyllis (Jay) Dolhinow (Semnopithecus entellus in India), Jane Lancaster (Cercopithecus aethiops in Africa), Donald Linburg (Macaca mulatta in India), and John Ellefson ( Hylobates lar, Southeast Asia) among others. Beginning in the early 1960s, Louis Leakey, the great paleoanthropologist, sent researchers to conduct long-term studies of the great apes. Leakey sent Jane Goodall to study chimpanzees (Pan troglodytes), Dian Fossey to study gorillas (Gorilla gorilla), and Birute Galdikas to study orangutans (Pongo pygmaeus). For the next 30 years, most studies of NHP in their natural habitat were carried out by students of Washburn or students of students of Washburn. Other early primatologists of note include Charles Southwick (Macaca mulatta in India), Stuart Altmann, (Macaca mulatta on Cayo Santiago), George Schaller (Gorilla gorilla in Zaire), and in Africa Thelma Rowell (Papio anubis), Han Kummer (Papio hamadryas), and Robert Hall (Erythrocebus patas).
The turning point in the development of the systematic collection of data on NHP was the 1974 article by Jean Altmann concerning sampling methods. Prior to 1974, data were collected ad libitum, that is, behaviors were recorded that were most easily observed. This method of observation resulted in an unsystematic data set not amenable to statistical analysis. After 1974, ad libitum methods gave way to more systematic observations that could be more competently analyzed by statistical techniques.
The first steps in the study of a group of primates is to habituate them to the presence of the researcher, and for the researcher to learn to recognize individual group members. The process of habituation can take a short or long period of time depending on many factors including the skills and endurance of the primatologist, the nature of the habitat, the prior experience of the primate group with people, and so forth. Once habituation is proceeding, data collection can begin. Successful data collection involves a stated problem or hypothesis, systematic methods of observations and recording, the use of an ethogram (or a defined list of behaviors that relate to the problem or hypothesis being tested), the identification of individual members of the group under study, and careful analysis of the data.
Fifty years of the study of the alloprimates resulted in many surprising and controversial discoveries. For example:
- Mating patterns do not necessarily follow from social systems. For example, a female (such as the patas monkey, Erythrocebus patas) may live in a polygamous social group but mate promiscuously.
- A species can have multiple social systems. Howler monkeys (genus Aloutta) and gray langurs (genus Semnopithecus), for example, may live in unimale groups or multi-male/multi-female troops.
- Multiple social systems may be adaptive to the same habitat. White-faced capuchins (Cebus cappuccinos) that live in multi-male/multi-female troops are sympatric in Central America with spider monkeys (genus Ateles) that have a fission-fusion social system.
- Among Old World monkeys, the fruit and insect eaters (subfamily Cercopithcinae) have larger brains for body size than the leaf eaters (subfamily Colobinae).
- Tool use has been observed among chimpanzees (genus Pan), orangutan (genus Pongo), and capuchins (genus Capucinus).
- For anthropoids, individual troop members recognize the vocalizations of other individual troop members, and vocalizations can have environmental referents such as bird or terrestrial predators.
- Social skills are more important in attaining and maintaining rank than body size or fighting ability.
- For anthropoids, but not prosimians, sexual intercourse may occur outside the female’s fertile period.
- For anthropoid primates, but not prosimians, both heterosexual and homosexual behavior has been observed.
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