aa.1956.58.3.02a00020

aa.1956.58.3.02a00020 - Individuality in the Behavior of...

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of Chnpanzees1 HENRY W. NISSEN Yerkes Laboratories of Primate Biology, Orange Park, Florida HE pronounced variability of behavior among a group of chimpanzees T was noted by the earliest students of this primate. R. M. Yerkes (1943) called the chimpanzee ‘‘a rugged individualist,” and no one who knows these animals has since found reason to question this description. All animals are of course individually variable, but such differences are certainly greater among the so-called higher animals; since they are more complicated, structurally and behaviorally, there are more ways in which they can differ. Man exceeds all other species in the combination of com- plexity and polymorphism, and the diversity of human behavior is well known. Variability among chimpanzees is perhaps less but, as I shall try to show, is still very impressive. To avoid later confusion, let me first dispose of a preliminary question. The early systematists divided contemporaneous chimpanzees into a number of species-from a conservative four up to as many as fourteen-and even today disagreement persists as to the number of living species. All the criteria of species differentiation have been of rather superficial characters. Skin color is one of these; the designations “white-faced” and “black-faced” are in common use today. But we now know that skin color is a function of at least three variables: age per se, amount of exposure to sunlight, and heredity. All chimpanzees are relatively light-faced when born, becoming darker as they get older; the rate of this change is a function of how much they are exposed to the sun. Some individuals never become as dark as others, but there is no evidence for reproductive isolation related to skin color. A receding hair line of the forehead is another irregular concomitant of advancing age which has been used as a species-differentiating character. I am no taxonomist and thus speak without authority, but for present purposes I shall assume with Schwarz (1934) that our current population of 57 chimpanzees, and all 151 of these apes that have been at the Yerkes Laboratories during the past 25 years, belong to the same species, Our discussion will therefore concern individual rather than species differences. Pan paniscus, the rare pygmy chimpanzee from south of the Congo, shows many marked deviations from all others and probably is a separate species. But since the behavior of paniscus has not been studied extensively, we cannot use it in a consideration of individuality. Chimpanzees vary widely in respect to physical characteristics. Adult weights range from about 65 to 160 pounds; males average some 9 pounds heavier than females, but there is considerable overlap. In general, sexual dimorphism is less pronounced in chimpanzee than in man. Body sizes and proportions vary considerably. One quickly learns to identify our 57 chimps by their faces; some have an Oriental “slant” to the eyes, others look like a cartoonist’s idea of an Irishman. It is a favorite game at the Laboratories to 407
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This note was uploaded on 04/05/2011 for the course ANT 154bn taught by Professor Debello during the Winter '10 term at UC Davis.

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aa.1956.58.3.02a00020 - Individuality in the Behavior of...

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