During the 1930s, C. Ray Carpenter carried out the first modern studies of free-ranging primates. In its scope, duration, systematic data collection, and revelations about the naturalistic behavior of primates, his research went far beyond all previous studies, such as those by Bingham, Nissen, Zuckerman, and Marais. Although his 1931 doctoral dissertation was on the behavior of pigeons in captivity, he immediately switched to field research on free-ranging primates. Over the next decade, in Central America, Southeast Asia, and the Caribbean, he carried out landmark field studies of howler monkeys, spider monkeys, gibbons, and rhesus macaques. The rhesus were on Cayo Santiago, a small island off Puerto Rico, in a colony established in the late 1930s with monkeys that Carpenter shipped from India. In the years since then, that colony has been the subject of research by many scientists.
After completing his doctorate with Calvin Stone at Stanford (1931), Carpenter began his primate field studies under a 3-year postdoctoral appointment to Robert Yerkes’s laboratory at Yale. Thereafter, he had professorial appointments in psychology at Columbia University (1934-1940) and in both psychology and anthropology, first at Pennsylvania State University (1940-1970), then at University of Georgia (1970-1975).
Although Carpenter was trained in psychology, his primate studies included a diversity of topics more characteristic of biology, including demography, manipulation and locomotion, foraging, ranging and territoriality, sexual behavior, mother-infant relationships, competition and cooperation, agonistic behavior, dominance relations, vocalization and communication, and grooming and play.
His field methods were essentially those of a descriptive naturalist, as he observed representative samples of populations on-site in their natural habitats and made accurate and detailed reports of his observations. He made several important contributions to the methodology of primate field studies, including (a) censusing groups as they progressed single file instead of when they were congregated; (b) breaking the complexity of ongoing interactions in a group into their more readily observed components, dyadic relationships; (c) gradually habituating animals to his presence and remaining at a distance at which he could observe them without undue disturbance; (d) taking advantage of available technology, including photography, sound recording, and playback equipment; (e) making objective records of behavior, often quantitative and checked when possible by repeated observation; and (f) taking representative samples, not just of the dramatic or unusual.
Carpenter was adamant about the potential of observational field studies to conform to the same canons of science that characterized laboratory research, including accuracy of records, adequate sampling, and data that permit “comprehensive description, measurement, interpretation and even prediction.” He was interested in theoretical frameworks that might have the potential to encompass the complexities of primate social processes, and in his search for unifying principles, he turned, at various times, to sociometry, semiotics, mathematical models, design features of language, dominance hierarchies, homeostasis, and cybernetic functionalism.
In five articles published in 1942 (two), 1952, 1954, and 1958, respectively, Carpenter featured his generalizations about primate grouping and social processes. These eclectic articles include many revelatory statements. Here is a small sample, rearranged and edited for brevity. Most are from Carpenter’s two earlier reviews, emphasizing his prescience and eclecticism, which went well beyond that of his contemporaries.
For the complete description of a group, each of the N(N — 1)/2 paired interactions among N individuals should be minutely described and measured for a number of different characteristics. The strength of the attachment between two individuals may be judged, or actually measured, by observing for a period of time the average distance which separates the two animals. (1942a)
A basic fact for primate societies is that all the individuals in a group are capable of perceiving and discriminating all the other individuals in the group and react discriminatively toward them. (1952)
A universal characteristic is that all social relations are, in varying degrees, reciprocal. A relatively high degree of interdependence in natural groupings of primates is an important characteristic of their social life. Perhaps such expressions as mutual aid, altruism, cooperation, and social service are too anthropomorphic in connotation, and thus may becloud the actual relationships, by provoking controversy. (1942a)
Charles Darwin and many natural historians following him have so emphasized “the struggle for existence” and competition that the facts of interdependence in animal societies have not been accurately and fully represented. As a result, the formulated theories and principles of social behavior are faulty, since they are build on inadequate factual bases. The survival and reproduction of groups of monkeys of a species depend on the social coordination—one may say cooperation—of all the individuals of the group. (1942b)
The monkey or ape in its natural group in the tropical forest has its freedom of movement strictly limited by the structure of its group. (1942a)
The ratio of adult males and females in a group seems to express a balance between the summed female sex needs or capacities in a group and the sexual capacities of the effective males available to satisfy the needs. (1942a)
Individuals in free-ranging organized groups deploy themselves in space in inverse relation to the strength of centripetal (cohesive) interactions and in direct proportion to the strength of centrifugal interactions. (1952,1954)
There is no question but that groups of monkeys and apes are organized around several dominance gradients (1942b)….However, when multimale-multife-male groupings of monkeys and apes are observed under “free-range” conditions and for long periods of time, rarely if ever does one male have complete priority to all incentives at all times (1952)….Also, measures of dominance show wide individual variations in the magnitude of dominance, a variation which is not accurately indicated by describing an order of priority or general relative aggressiveness. (1942a)
In a concerted attack on the group, individuals may be killed, but this is incidental to the fact that the group survives and the species is perpetuated. (1942b)
In the years after completing his investigations of sexual behavior on the rhesus of Cayo Santiago, Carpenter’s research was devoted primarily to educational films and television. He produced several documentary films on free-ranging primates, recensused the howler monkeys on Barro Colorado, and wrote several reviews of behavior in free-ranging primates. In 1971, Carpenter undertook his last fieldwork. He collaborated with José Delgado and others in their study of gibbons on Hall’s Island, Bermuda. The object of the study was to induce lasting modifications of free-ranging behavior by means of remote, long-term stimulation of the brain.
Starting in the mid-1950s, research on free-ranging primates has been doubling about every 5 years, much faster than science as a whole, which doubles every 15 years. By comparison, at the time of Carpenter’s early investigations, in the 1930s, no one else was actively engaged in such studies. Under the circumstances, his accomplishments are remarkable.
- Carpenter, C. R. (1964). Naturalistic behavior of nonhuman primates. University Park: Pennsylvania State University. [Note: Carpenter’s major primate field study reports and several reviews are reprinted in this volume]
- Haraway, D. (1983). Signs of dominance: From a physiology to a cybernetics of primate society, C. R., Carpenter, 1930-1970. Studies in the History of Biology, 6, 129-219.
- Montgomery, G. M. (in press). Place, practice, and primatology: Clarence Ray Carpenter, primate communication and the development of field methodology, 1931-1945. Journal ofthe History of Biology.
- Rawlins, R. G., & Kessler, M. J. (Eds.). (1986). The Cayo Santiago macaques: History, behavior, and biology. Albany NY: State University of New York.