PRIMATE ORIGINS OF SOCIETY (Introductory Level) (Psychology, Biology, Sociology 221a) Course Instructor Sydney Perloe Haverford College Haverford, PA USA Telephone: 1-610-896-1234 Fax: 1-610-896-1224 Email: sperloe@haverford.edu Average class size: 25 Fall 1995 The syllabus is aimed at orienting you to the material that is assigned. Please read the relevant background material before going onto the actual assignment and use it to help you organize the information in the readings. You should have completed the readings by the meeting for which they were assigned. When assignments cover more than one meeting, try to complete the readings as early in the time period as you can. I. Introduction A. Primatology: history and orientation Our set of readings begins with a brief history and overview of the interdisciplinary field of primatology. Primatologists study prosimians, monkeys and apes at many levels ranging from genes and organismic process to primate "proto-cultures." The first selection by Hinde presents a framework that allows us to integrate phenomena from all of these levels. His hierarchical scheme composed of behaviors, interactions, relationships and structures, is used very widely. His second selection points to the linkage of physical and behavioral characteristics of interacting animals in adaptive complexes, that embody major strategic directions taken by the members of a species as they deal with the problems of adaptation. Both the bodily structure and the behavioral components of these complexes are affected by natural selection. The excerpts from Dunbar present the four questions that comprise the evolutionary approach to the study of behavior. i.e., the questions of proximate cause (or mechanism), development (or ontogeny), function and evolutionary history. Each question can be asked about any behavior we wish to examine; answers to all four questions are required for a full explanation of any behavior. Sept. 6 1. Perloe, S. About primatology. pp. 1-4. 2. Hinde, R. (Ed.) Primate Social Relationships. Preface, (through first paragraph on p. xi); Chap. 1, A conceptual framework, pp. xi-7. 3. Hinde, R. The Biological Basis of Human Behavior, Excerpt from Chap. 26, Adaptive differences in group structure, pp. 395-398. 4. Dunbar, R. Primate Social Systems, Excerpt from Chap. 1, Primates and their societies, pp. 1-9. 5. Burton, F. Non-human Primates. CD-ROM (on reserve). Take a few minutes to familiarize yourself with this resource so that you can refer to it when we discuss particular species. It may also be helpful in selecting the species on which you want to report. B. Basic concepts and principles We begin with the evolutionary orientation that guides current work on primate social systems. At this point our goal is to orient rather than to achieve mastery of the theory. The mastery goal will be approached slowly as we use the orientation to help us understand the everyday social lives of monkeys and apes and read more theoretical material throughout the semester. The two chapters by Barash provide a primer of modern Darwinian theory, that is, the theory of evolution by natural selection, and its application to the study of behavior. This is the perspective that guides primatology. Although Barash labels his approach sociobiology, the basic concepts he presents are also employed in behavioral ecology. The theory is most concerned with the function of behavior. The excerpts from Dunbar in this section give a more advanced treatment of the central, reproductive meaning of fitness and the difference between selection based on benefits to an organism's group and selection based on benefits to an organism's genes. He shows that fitness involves the solution of three problems, survival, reproduction and rearing offspring. The final part of the Dunbar selection discusses the various ways in which genes might influence behavior and the role played by genes, environment and an organism's decision processes in the determination of behavior. Sept. 8-11 1. Barash, D. Sociobiology and Behavior, 2nd ed., Chap. 2, How it works; Evolution as a process, pp. 11-25; Chap. 3, Evolution and behavior; Getting it together, pp. 27-44. Think about the answers to the study questions at the ends of the chapters. 2. Dunbar, R. op.cit., Excerpt from Chap. 2, Theory of Reproductive Strategies. pp. 15-28. Sept. 10 ZOO TRIP (Details to be arranged.) (Sunday) Sept. 13 Quiz 1 II. Baboons A. Savannah baboons Sept. 15-25 Savannah baboons, Papio anubis (olive baboons), Papio cynocephalus (yellow baboons) and Papio ursinus (chacma baboons) were the first primates to be studied at length in their natural habitats. The selection was based partly on their relevance to the search for a model of how primates evolved. Most live in the open, grassland settings that are believed to be the place in which the first hominids evolved. Savannah baboons were also chosen because it is easier to see and follow animals on open grasslands than in forests. Some savannah or common baboons, like the ones at Gombe, also live in the forest. The groups studied by Smuts and Strum lived in the more typical savannah setting. Despite the differences in the settings in which savannah baboons have been studied, their social structures are very similar. Later readings by Kummer and by Sugawara will describe some exceptions to this generalization. The groups examined in the Smuts and Strum readings were neighbors. In fact some of the same animals appear in both studies. The books are rather different in style, one is closely tied to data that are presented along with the verbal descriptions and explanations. The other is a personal narrative account whose supporting data is not given. (It is given in a variety of journal articles and book chapters.) Smuts provides us with an introduction to the species and her own study. Then we go to Strum's description of her personal introduction to the ~Pumphouse Gang~ and the introduction of a young transfer male. Although interactions among the males provide the most dramatic moments in baboon communities, it is the interactions and relationships among females and between females and their offspring that constitute the enduring core of baboon social organization so that this is where we move next. Relationships among males and between males and females are then examined together because males usually interact with each other in the context of male-female interactions. We end with the puzzling relationships between males and infants and a consideration of the psychological mechanisms involved in friendships between males and females. 1. Smuts, B., Sex and friendship in baboons. (Required text) Forward and Chaps. 1-3, pp. xi - 36. 2. Strum, S., Almost human: a journey into the world of baboons. Chaps. 2-3, pp. 23-53. 3. Smuts, op. cit. Chap. 7. pp. 123-156. (Note: You are not responsible for statistical details or procedures in this or any of the other chapters. You need to be able to describe the results in words, but you need not remember the exact numbers or understand the actual statistical operations.) 4. Strum, op. cit. Chaps. 6-7, pp. 83-104. 5. Smuts, op. cit. Chaps 4-6, pp. 37- 122; Chaps. 8-9, pp. 159-234. II. Baboons B. Hamadryas baboons Hamadryas baboons (Papio hamadryas) live in very arid areas of Ethiopia and Saudi Arabia. Although they are very similar in appearance and basic individual behavior patterns to savannah baboons, they have a strikingly different social structure. They have not been studied as extensively as their common cousins, partly because of their inaccessibility and partly because most of them live in a region that was embroiled in war for many years. Kummer's classic study gives us an overview of their social structure and of the interactions and relationships that make them different than savannah baboons. It also provides information about how hamadryas males and females develop their social behavior patterns. Sept. 27 1. Kummer, H. Excerpts from Social Organization of Hamadryas Baboons, Chap. 1, secs. 2-5, pp. 5-14, Chap. 4, pp. 29-83. (Read summary on pp. 81-83 before reading entire chapter.). C. The source of the hamadryas - savannah difference Comparing savannah and hamadryas baboons allows us to deal with two questions: what is the evolutionary history of the hamadryas pattern and which dispositions seem to be most involved in the difference between the social structures in which the two species live. Baboons are unique in allowing us to see how small variations in dispositions can give rise to striking changes in social structures. The comparison also provides a good example of how dispositions interact with environmental settings to produce the social structures we observe. This understanding should help us when dealing with other primate species where the data are not as clear. Throughout a wide range of settings, e.g.,those at Gombe and at Gilgil, baboons have the social structure pattern described by Smuts ans Strum. This has led some, like Kummer, to describe their social systems, especially the male-female relationships aspect, as phylogenetic adaptations. He sees these patterns as adaptations whose form is narrowly constrained by genetic developmental programs. In contrast, he points to adaptive modifications, whose underlying programs lead to variations in response to varied environments. For example, baboons generally sleep in trees, but when trees are scarce, they sleep on steep rock formations. Although Kummer dichotomizes adaptive behavior systems, it is likely that there are also evolved behavior systems that show intermediate degrees of flexibility. Evolved behavior systems that adjust, to a greater or lesser extent, to changes in settings are called facultative; those that operate the same way in all of the settings in which a species lives are called obligatory. Hamilton and Bulgar suggest that male-female relationships may be more facultative than Kummer believed. It is important to recognize that facultative patterns do not vary arbitrarily, at the whim of the creatures involved. Rather they vary in a systematic way with variation in the environments in which they develop or operate. Much of behavioral science is aimed at discovering principles that describe the relationships between variations in environmental inputs to facultative behavior systems and the behaviors they produce. The distinction between obligatory and facultative patterns of behavior is very important for understanding human behavior from an evolutionary perspective. The environments in which virtually all humans live today are very different than the ones in which they evolved. Understanding the impact of this change requires that we recognize the extent to which our evolved adaptations are facultative and just how the flexible adaptations respond to particular environmental features. This problem will be addressed directly in the next section, particularly in the selection by Tooby and Cosmides. The contact between savannah and hamadryas baboons has given rise to hybrids whose behaviors provide still more information about the source of the differences in social structures of the two species. The excerpts from Sugawara point to variation in male dispositions as the basis of the structural contrast. Sept. 29 1. Kummer, H. Primate Societies. Chap. 5, How flexible is the trait?, pp. 131-142. 2. Hamilton, W. and Bulgar, J. Facultative expression of behavioral differences between one-male and multimale savanna baboon troops. American J. Primatology, 28, 61-71. 3. Sugawara, K. Excerpts from Sociological comparison between two wild troops of anubis-hamadryas hybrid baboons. African Studies Monographs, 1982, 2, pp. 73-74, 120-122, 124-128. III. The Evolution and Operation of Dispositional Adaptations Oct. 2-9 A. Modules of the mind: the human language adaptation The most distinctive human adaptation is the use of vocal language. We are disposed to learn and use language with a particular grammatical structure that is shared by all known human languages. The chapter by Pinker, a psycholinguist, argues for recognizing the innate nature of the mechanism(s) that enables us to do what only humans can do, namely speak a language. He presents a simple scheme for understanding how innate mechanisms are affected by genes and environment as well as by the experiences we have that are themselves the consequences of innate mechanisms operating in an particular context. His model is very compatible with the one implicit in the four questions described by Dunbar, in Section I. Pinker contrasts two views of the human mind. The first, the Standard Social Science Model, holds that humans have a single general learning mechanism that allows them to acquire all of their behavior patterns and that is equally open to acquiring any behavioral pattern our muscles and glands can produce. The second, the Modular view, proposes that we have a large number of specific behavior modules, each of which has evolved to deal with a particular adaptive problem. The modules vary in the extent to which they produce different outputs in different contexts. The best example we have of such modular functioning is in the learning and use of language. Pinker lists a variety of other possible, adaptive modules. Dispositions and modules refer to the same underlying brain mechanisms or structures that produce behaviors. 1. Pinker, S. The language Instinct, Chap. 13, Mind design. pp. 404-430. B. Species-typical adaptations as "designs" for adaptive behavior Tooby and Cosmides continue the examination of behavior generating brain mechanisms, which they call adaptations. They present a searching analysis of the distinction between general purpose behavioral mechanisms and ones that are designed to achieve specific, adaptive functions. Their discussion supports the view that evolution has resulted in a large number of specific mechanisms, each of which is designed to solve a narrow class of problems faced by organisms in the setting where the mechanism evolved. This historical context is called the environment of evolutionary adaptedness (EEA). Tooby and Cosmides criticize the correspondence view that evolution has resulted in a general, inclusive fitness maximizing mechanism, capable of generating adaptive responses in settings that are very different than the ones in which the mechanism evolved. The correspondence view is held by some primatologists who are behavioral ecologists, e.g. Dunbar. However, because these primatologists generally carry out their studies in natural settings that have changed little from the EEA, their findings do not necessarily support the existence of a general inclusive fitness maximizer. On the other hand, the two evolutionary approaches produce rather different expectations about the adaptedness of behavior in modern, human societies. Tooby and Cosmides' treatment also elaborates Pinker's distinction between the environmental contribution to the development of a mechanism, i.e., ontogeny and the environmental inputs that stimulate the operation of a developed mechanism. Differences between present environments and the EEA can affect the current adaptiveness of an evolved adaptation through the impact on the adaptation's development or operation. Evolved adaptations that were very useful in the EEA may be quite maladaptive in modern contexts. 1. Tooby, J. and Cosmides, L. Excerpts from The past explains the present: emotional adaptations and the structure of ancestral environments. Ethology and Sociobiology, 1990, 11, (read the sections within the following sets of page number ranges) 375-378, 384-387 (up to end of 1st. par.)388-389, 394-398, 399-402 . C. Physiological mechanisms involved in the generation of species-typical social structures Both Pinker and Tooby and Cosmides deal with adaptive mechanisms or dispositions mainly on theoretical level. The next selection, by Mendoza and Mason, shifts the focus to some of the physiological systems involved in the operation of adaptive behavior mechanisms. They identify some endocrine and autonomic nervous system correlates of species differences in social dispositions. The organismic systems they identify are probably "downstream" from the brain mechanisms that embody the dispositional adaptations. That is, they are probably monitoring the pathways through which the innate brain mechanisms involved in social adaptations actually generate behavior. Except for the studies of aphasia, described by Pinker, we know relatively little about the brain mechanisms involved in behavioral adaptations. It is very likely that they involve circuits in the limbic system, concerned with emotion, as well as in the frontal cortex, concerned with integrating and planning action. Both of these parts of the brain influence the physiological systems discussed by Mendoza and Mason. 1. Mendoza, S. and Mason, W. Constitution and context: the social modulation of temperament. In J.J. Roeder et al. (Eds.) Current Primatology, Vol. II. pp. 251-256. IV. Behavioral Ecology Earlier, we described two approaches to primatology, sociobiology and behavioral ecology. While the two share a basic evolutionary orientation, sociobiologists focus on the impact of social strategies on behaviors closely related to reproduction, e.g. competition for mates, acquiring and maintaining dominance ranks, and incest avoidance. The alternative approach focuses on strategies oriented toward getting food and protection against predators. As a result, behavioral ecologists pay a great deal of attention to the ecological setting in which a group lives in order to discover what kinds of food are available and how these resources are distributed in space and over time. Our examination of baboons included information from both approaches, but depended most heavily on sociobiological analyses. In this unit we will emphasize behavioral ecology. Oct. 11-13 A. The Behavioral Ecology and Social System of Squirrel Monkeys Our introduction to behavioral ecology comes through the work of Dr. Sue Boinski, a biological anthropologist, who has studied new world monkeys, especially squirrel monkeys. The cat sized, squirrel monkey is one of the most common monkeys in South and Central America. It is an extremely active animal that runs about through the middle and higher levels of trees in the forest. Despite its ubiquity, its size, speed and habitat make it difficult to study in the wild. Most of what we know about squirrel monkeys comes from studies of groups in captivity. Dr. Boinski is one of the few primatologists who have done long term studies of squirrel monkeys in their natural habitats. We can describe squirrel monkey behavior and interaction patterns in considerable detail, but there is more uncertainty about the relationships and social structure of the one or more species in this genus. These relationships vary considerably between the mating and birth seasons. During the most of the year, males and females have little to do with each other. Although the males sometimes fight each other furiously, they also seem to have close affiliative relationships. Squirrel monkeys have some curious, genital display patterns that are involved in agonistic and affiliative relationships. Because they are small and easy to maintain, squirrel monkeys have been a favored laboratory research animal. There has been considerable work on brain and other physiological components of squirrel monkey behavior patterns. The first paper in the set points to the likely impact of predation pressure and seasonal fluctions in food abundance in determining the narrow window during which squirrel monkey females give birth. The next item in the set, by Janson and Boinski, deals with how a species~ bodily characteristics, e.g., size, and its behavior patterns contribute to its ability to exploit potential food resources in its environment. Boinski and Timm provide an example of such exploitation in a paper about how monkeys (and predatory birds) are able to get at a particular species of bat. The last two papers in the set move beyond specifically ecological concerns. One deals with the way female vocalizations allow squirrel monkeys to keep in touch as they forage through the dense foliage of trees. The other looks at male squirrel monkey mating patterns. 1. Be sure to browse the New World Monkey section of the Burton CD-ROM before you begin reading the items sent by Dr. Boinski. 2. Boinski, S. Birth synchrony in squirrel monkeys (Saimiri oerstedi). Behavioral Ecology and Sociobiology, 1987, 21, 393-400. Optional reading 3. Janson, C. and Boinksi, S. Morphological and behavioral adaptations for foraging in generalist primates: the case of the cebines. American J. of Physical Anthropology, 1992, 88, 483-498. 4. Boinski, S. and Timm, R. Predation by squirrel monkeys and double-toothed kites on tent-making bats. American J. of Primatology, 1985, 9, 121-127. 5. Boinski, S. The coordination of spatial position: a field study of the vocal behavior of adult female squirrel monkeys. Animal Behavior, 1992, 41, 89-102. 6. Boinski, S. Mating patterns in squirrel monkeys (Saimiri oerstedi): implications for seasonal sexual dimorphism. Behavioral Eco;ogy and Sociobiology, 1987, 21, 13-21. Oct. 18 B. The Evolution of Group Living With very few exceptions, primates live in organized groups. While it is easy to conceive of the benefits of group living, it is important to recognize that this mode of life also carries costs. The costs are high enough to raise the question of why primates are such gregarious animals, that is, which selective pressures gave group living animals sufficient benefits to outweigh the costs of group life. A related, but separate, question arises in response to the enormous variations among species in the structures of their societies. Which selective pressures lead each species to develop its species characteristic form of society? Behavioral ecologists have been particularly interested in these questions. Wrangham's paper presents a very influential hypothesis about the ecological setting that made female bonded social structures, so common among terrestrial and semi-terrestrial species. He was among the first to recognize that the evolution of a species' social structure depends primarily on what helps females, in a particular ecological setting, gain a competitive advantage in access to food . The spatial distribution of food is the aspect of the setting that is critical in shaping female social relationships. If the distribution gives one pattern of social organization among females a clear advantage over others, males will adapt to that pattern. VanSchaik revises and extends Wrangham's hypothesis. First he notes that there are two forms that competition over a resource can take, scramble competition and contest competition. He also examines the separate effect of competition between females belonging to the same group and between females belonging to different groups. In contrast to Wrangham, VanSchaik believes the the distribution of food does not influence whether animals evolve a gregarious, as opposed to an independent living strategy. He holds that the selection of group living occurs in response to predation pressure. 1. Wrangham, R. W. Ultimate factors determining social Structure In R. Hinde (ed.), Primate Social Relationships. Chap12.2, pp. 255-262. 2. Van Schaik, C. Excerpts from "The ecology of social relationships amongst female primates." In V. Standen and R. Foley, (eds.), Comparative socioecology: the behavioral ecology of humans and other mammals., pp. 195-217. Oct. 20 Review and Catch up Oct. 23 Midterm V. Macaques Macaques are the most widespread non-human primate genus, ranging from Morocco and Gibralter in the west to Japan in the east and from the tropical rain forests of Indonesia to the winter snows of Japan. They are primarily forest living, but have adapted very well to living alongside humans. The selections from Fedigan and deWaal describe general aspects of the two most studied species, rhesus (Macaca mulatta) and Japanese (Macaca fuscata) macaques. These species, along with the crab-eating (M. fascicularis) and pigtailed (M. nemestrina) macaques have fairly similar social structures. However, there are some species, e.g., the barbary (M. sylvanus), bonnet (M. radiata) and stumptail (M. arctoides) macaques that differ from the familiar macaque pattern. The Burton CD-ROM provides information about the many other macaque species. While you are not expected to remember the names or details about every one of the macaque species, you should have an idea of the extent of their distribution and the kinds of similarities and differences that are found among them. We will rely on class reports for part of our coverage of macaques. The rhesus/Japanese macaque social structure epitomizes the female bonded pattern described by Wrangham. Because the most central features of such societies are the kinship and rank relations among females, we begin our detailed examination of these societies with a study of the routes through which females acquire and maintain their ranks. Chapais has done the most important experimental studies of these processes. These studies grew out of earlier field research. He was a Philips Lecturer at Haverford last year and presented two talks about his work and about rank related behavior among female macaques. Tapes of these are on reserve in Magill Library as is the edited set of excerpts from the talks. Oct. 25-30 A. Japanese and Rhesus macaques (Background) 1. Fedigan, L. Primate paradigms, Ch. 14, a section on Japanese Macaques, pp. 218-223. 2. deWaal, F. Peacemaking Among Primates. Excerpts from Chap. 3, Rhesus Monkeys, pp. 89-104. B. Kinship and Rank 1. Chapais, B. and LaRose, F. Experimental rank reversals among peers in Macaca fuscata: Rank is maintained after removal of kin support. American J. Primatology, 1988, 16, pp.31-42. 2. Chapais, B. Selections from videotaped talks, November, 1994. (On reserve.) C. Migration and group splitting 1. Perloe, S. Joining a group on Cayo Santiago: a case study. (American Society of Primatologists, 1993.) D. Macaque Reports VI. Conflict, Cooperation and Reconciliation Nov. 1 A. Dominance Two fundamental aspects of social life in any primate species are conflict and cooperation. Much of our examination of the social systems of baboons and macaques was concerned with these processes so that the concepts examined here are already familiar. However their central importance justifies additional attention. The aspect of social conflict that has been studied most intensively is dominance, a relationship between two animals in which one reliably yields to another when the possibility of conflict between them arises. It is essential to recognize that dominance is not a feature of an individual animal, but a feature of a relationship between animals. The same animals can be dominant in some relationships and subordinate in others. In many primate societies, dominance relationships are patterned hierarchically, that is, when A is dominant to B, A is also dominant to all animals that are subordinate to B. An animal's place in a hierarchical dominance structure is often referred to as its rank. The evolutionary perspective focuses on four sets of questions about dominance relationships: Function. What do the partners in the relationship get out of it (in both the short and long term)? Mechanism. Which psychological processes make an animal behave in a dominant or subordinate way in a relationship? Development. What events in the life experiences of an animal affect its rank? How do animals acquire their ranks? Evolution. The major question asked here is about the relationship between ranking systems among non-human primates and human ranking systems based on power and prestige. DeWaal describes the interactions involved in dominance relationships and some of the confusions that have arisen in attempts to measure dominance. He points out that both parties benefit from dominance relationships and shows that dominance relationships are linked to cooperation as well as conflict. Although his major concern is with the description of dominance relationships and their relatively short term functions, deWaal's discussion of a possible dominance drive also touches on the mechanism question. We will discuss this question more fully in class. Walters and Seyfarth's discussion of cooperation, conflict and dominance is more broadly focussed than deWaal's. They deal with the development and long term functions of dominance relationships as well as with patterns of affiliative relationships, especially those involving grooming. Both grooming and dominance related interactions seem to involve mechanisms that produce social relationships rather than immediate material benefits to the participants. The excerpt from Silk's chapter is concerned with the long term functions of dominance rank. She identifies what theory leads us to expect about functions and indicates problems in assessing whther these functions are actually served by attaining high rank. 1. deWaal, F. Dynamics of Social Relationships. In Smuts, B. et. al., (Eds.) op. cit., Chap. 34, pp. 421-429. 2. Walters, J. R. & Seyfarth, R. M. Conflict and Cooperation. In Smuts, B. et. al., (Eds.) op. cit.,, Chap. 25, pp. 306-317. 3. Silk, J. Excerpt from Social Behavior in Evolutionary Perspective . In Smuts, B. et. al., (Eds.) op. cit., Chap. 27, pp. 318-324. Nov. 3 B. Reconciliation Contrary to everyday understanding, conflict and cooperation are closely linked social processes; animals cooperate in order to compete more effectively. Because of the nested structure of primate societies, where individuals are linked into relationships, that are in turn linked into broader relationships, lines of conflict must often be bridged to form higher level alliances. DeWaal has been the main researcher to identify reconciliation and to discuss the part it plays in the maintenance of primate social systems. He notes that reconciliation simultaneously reinforces dominance relationships and facilitates cooperation between dominant and subordinate partners. The two sets of excerpts illustrate species differences in reconciliation. They are written in a popular way, but they are based on research that has been published in a fully documented format. 1. deWaal, F. Peacemaking among Primates. Excerpts from Chap. 3, Rhesus monkeys, pp. 110-122, and Chap 4, Stumptail monkeys, pp. 154-163. VII. Gelada Report We now move away from the heavily studied macaque and papio (baboon) genera in order to get a fuller view of the variety of social systems generated by primates. While all of these systems result from the operation of the same set of evolutionary processes operating on varied phyologenetic lines in varied settings, we will want to be sensitive to the surface differences as well as to the underlying continuities across primate era. The background readings provide either a brief overview or a sample of research on a species. Try to identify the major forms of relationships and structures in each of the species and to think about the conditions that might have led each species to evolve as it did. Be sure to browse the Burton CD-ROM for each of the species covered. The first ~novel~ species we consider is geladas. Although they are often referred to as baboons and live in a habitat that overlaps the one occupied by some baboons, they are not classified in the same genus as baboons and they utilize the habitat quite differently. Despite the similarity between hamadryas and gelada social structures, i.e., one male units that form larger bands, the structures grow out of different patterns of relationships. Nov. 6 1. Fedigan, L. Excerpt from Primate Patterns, Chap. 15, pp. 248-252. VIII. Langur Reports Most species of langurs are forest dwelling, arboreal animals, but the hanuman langurs described by Hrdy live in mixed forest and scrub near an Indian town and spend much of their time on the ground. The general form of social organization, namely, small, one-male, bisexual groups and small, all-male groups seems common throughout the genus. At one time there was much controversy over the pattern of males taking over bisexual groups by ousting the resident male and then killing unweaned infants. Some believed that it was a peculiarity bred by the overcrowding and disorganization found among monkeys living near humans. Although the pattern is less frequent in some settings than in others, it has now been found in uncrowded groups living far from humans as well as in ones like those studied by Hrdy. Hanuman langurs have several other unusual patterns, besides infanticide, that distinguish them from species we have studied. For example, female kin have close relationships with each other, but they do not form female bonded societies or strong ranking systems and infants spend unusual amounts of time awy from their mothers, even on the first day of life. Nov. 8 1. Hrdy, S. Infanticide as a primate reproductive strategy. American Scientist, 1977, 65, pp. 40-49. IX. More New World Monkeys Reports About 35 million years ago, South America was a large island, lying much closer to the coast of Africa than it does today. It was a time at which earlier prosimian forms were beginning to give rise to the anthropoid radiation of monkeys and apes. Some of the monkey-like forms reached South America on tectonic islands that broke away from the African land mass and drifted across the narrow South Atlantic. These trans-Atlantic voyagers were the ancesters of modern new world monkeys. Although they resemble each other in many ways, old and new world monkeys have evolved separately since the initial migration of ancestral forms. The two sets of monkey families are most easily distinguished by the shapes of their noses. Old world monkeys have downwardly pointed nostrils that are side by side, as in humans; new world monkey nostrils open to the side and are spaced apart from each other. A few species of new world monkeys also have prehensile tails that function as fifth limbs and aid the animals in moving and feeding in the trees. All new world monkeys live in the trees all or almost all of the time. This is a dramatic change from most of the old world monkeys we have studied. The distribution of food and the dangers of predation are different for tree living than for ground living monkeys. Some of the differences in social systems between the two sets of animals can be traced to differences in the ecological settings in which they live. Nov. 10 A. Muriqui (Wooley Spider Monkeys) Muriqui are among the largest new world monkeys. Most of what we know about them comes from the studies of Karen Strier (a Swarthmore grad). Someone who thought that all monkeys were like baboons and rhesus macaques would be confounded by the muriqui. Neither males nor females seem to develop dominance relationships. Aggression is extremely rare within groups (perhaps not between groups). Females migrate and males generally stay in their natal groups. The differences between baboons and macaques, on the one hand, and species like muriqui, on the other, challenge us to understand the origins of variation in primate social systems. We will discuss the implications of this variation for understanding human evolution at the end of the semester. 1. Strier, K. New world primates, new frontiers: Insights from the wooley spider monkey, or muriqui (Brachyteles arachnoides). International J. Primatology, 1990, 11, 7- 19. B. Howler Monkeys Howler monkeys have the distinction of being the subjects of the very first scientific field study of primate behavior (Clarence Carpenter's 1934 study of the Barro Colorado Howlers). Because they are large, noisy and slow moving they have been the subject of many studies, despite the fact that they often live very high in the trees in very dense rain forests. It is difficult to identify the major relationships that hold howler groups together. They are certainly not female bonded like many macaques and baboons, nor do they seem to have particularly strong relationships among males or even between males and females. Some features of their social structure resemble the ones seen among langurs, but others do not. The paper by Crockett focuses on the problems in understanding howler females, but aspects of male behavior are equally problematic. 1. Crockett, C. Family feuds. Natural History, 1984, 93 (8), pp. 54-62. X. Ape Reports The first representatives of the hominoid family of primates (humans, great apes and lesser apes) first appeared in the fossil record about 20 million years ago. Modern hominoids are tailess, have shoulder joints that permit a much greater range of arm movement and hip joints that permit a much greater degree of leg extension than is true of monkeys. These were probably adaptations that helped apes move through trees and feed while hanging from branches, rather than by walking on branches, as monkeys usually do. The skeletal modifications also served as preadaptations for upright posture and bipedalism, that were so important in the evolution of the hominid subfamily. (Humans are the only living hominids.). They are also characterized by proportionately larger brains and longer periods of immaturity than is found among monkeys. Each of the living ape genera has a very distinctive form of social organization. Some ape social systems, such as those of chimpanzees and bonobos are extremely complex; others, like those of orangutans, are very simple. Despite their variation, all share the absence of female bonded social systems. While females have very close relationships with their immature offspring and sometimes their mature offspring, they do not have long term relationships with adult sisters, cousins, neices, grandaughters, etc. . This is linked to the fact that among all ape genera, most females leave the social units into which they are born. Among chimpanzees, bonobos and occasionally gorillas, males stay in their natal units. Primatologists are interested in apes for two reasons; first, they provide information about the diverse ways in which primates can solve adaptive problems and (like all other categories of animals). That is, they provide data about general socio-ecological principles. Second, they are our closest living relatives. Chimpanzees and humans may have shared a common ancestor as recently as 5 million years ago. Some primatologists believe that this close relationship allows us to use aspects of modern ape social systems to model the kind of system in which pre-human hominids lived. (See XII. B., below.) The social system of early hominids was a crucial part of the EEA (See III. B., above) in which the social dispositions of modern humans evolved. We will discuss this possibility at the end of the course. For now, we will concentrate on understanding the modern ape societies. Nov. 13 A. Gibbons and Siamangs The lesser apes have fairly similar social systems and are among the few monogamous primates (Several new world species, including the titi monkey, are also monogamous.) Despite living together for most of their adult lives, gibbons and siamangs would not make very good subjects for romantic novels. They do help us to identify the circumstances that make monogamy an adaptive pattern and to identify processes, other than emotional attachment that can produce the pattern. (In contrast, titi monogamy does appear to involve a strong emotional attachment. See III. C., above.) 1. Leighton, D. Excerpt from Gibbons: territoriality and monogamy. In Smuts, B. et al., (eds.) op. cit., pp. 135- 141 B. Orangutans Orangutans present many puzzles. They are very large and ungainly, yet they live high in the trees where they have difficulty moving about. Skeletons of orangutans show evidence of many healed broken bones, most likely caused by falls. In captivity, they are very capable learners, but their behavior in the wild shows little evidence of either great social or material intelligence. They belong to an animal family noted for the complexity of its social systems, but they appear to live an almost asocial existence. Part of the confusion may stem from our knowing so little about them. They live high in the trees in very inaccessible areas, that are being destroyed very rapidly by logging. 1. Rodman, P. and Mitani, J. Excerpt from Orangutans: sexual dimorphism in a solitary species. In Smuts, B. et al., (eds.) op. cit., pp. 146-150. Nov. 15 C. Gorillas Gorillas present still another variant of the one-male group social structure. While most of the detailed information we have about the species come from the long term studies of mountain gorillas begun by Dian Fossey, the general form of gorilla social structure appears to be common to groups living in other areas. Gorillas have very large intestines that allow large amounts of leafy matter to be digested slowly. The pointed shape of gorilla heads is due to powerful jaw muscles that arch over the skull and give gorillas the ability to chew very coarse vegetation. These adaptations permit gorillas to extract much of their nutrition from very low quality food, that is very abundant. A typical one-male group need not travel very far to the food it needs, but its members do have to spend a lot of time eating and digesting. Most of the time gorillas eat and rest peacefully, but occasionally there are very violent encounters between groups or between lone males and groups. A male sometimes bites so strongly that he buries his canine teeth in the skull of his opponent. Lone males sometimes attack females and kill their infants. The dominant silverback (fully mature males have grey hair on their backs) is generally very tolerant and protective of immature group members, most of whom are likely to be his offspring. Relationships between the silverback and adult female group members are generally relaxed, while those among the adult females are distant or mildly hostile. 1. Stewart, K. and Harcourt, A. Excerpt from Gorillas: Variation in female relationships. In Smuts, B. et al., (eds.) op. cit., pp.155-160. XI. Chimpanzees Chimpanzees have the most complicated social system yet encountered among non-human primates. It is characterized by shifting sub- groupings of individuals belonging to a larger community. The confusing pattern of coming and going at first led primatologists to think that chimpanzees had completely open societies, in which animals could join and leave groups freely. They also seemed to be remarkably relaxed about mating, with males apparantly uncompetitve about sharing mating opportunities with estrous females and females ready to mate with all interested males. However, the long term (over 25 years) studies of Japanese researchers and Anglo-American researchers at two sites along Lake Tangyanika, revealed that there were group boundaries and that there was competition among males and among females in a single community as well as between groups. Nov. 20 A. Field studies The overview chapter by Nishida and Hiraiwa-Hasegawa describes the general features of chimpanzees in the context of a comparison of chimpanzees and bonobos. We will deal with the comparison when we discuss bonobos. The best known chimpanzee researcher is Jane Goodall. We have assigned only parts of one chapter of her book about more than two decades of research at Gombe. Her writing presents exceptionally rich portrayals of individual animals as well of the patterns of interactions and relationships that characterize the community. 1. Nishida, T. and Hiraigawa-Hasegawa, M. Excerpt from Chimpanzees and bonobos: cooperative relationships among males. In Smuts, B. et al., (eds.) op. cit., pp.165- 172, 174-180. . 2. Goodall, J. Excerpts from The Chimpanzees of Gombe, Chap. 7, A Unique Society, pp. 146-159, 166-171. Nov. 22-29 (Have a Nice Thanksgiving Holiday , Nov.24-26) B. The Arnhem zoo study The deWaal book, Chimpanzee Politics, deals with a captive group whose demographic structure is very different than that of a natural chimpanzee community. Despite this difference, the patterns he describes are extremely similar to those described by Goodall, except for relationships among adult females and, perhaps, for the part played by adult females in the changing dominance relations among adult males. Make an effort to connect the information derived from the two settings in which chimpanzees have been studied. 1. deWaal, F. Primate Politics, Chaps. 1 - 5, pp. 53- 214. XII. Bonobos Bonobos are the most recently recognized species of ape. They belong to the same genus as chimpanzees (Pan), whom they resemble in many ways. To some extent, they have replaced the 1960's view of chimpanzees as the focus of the desire for a peaceful, sexy model of what we wish our ancestors might have been, viz. a primate living in golden age of joyous innocence before the fall into hominid self-consciousness. The excerpt from DeWaal's chapter on a captive group describes some of the behavior patterns that make bonobos so interesting. The remainder of the chapter by Nishida and Hirai-Hasegawa provides information from the studies of wild groups. Just as was true of chimpanzees, it is likely that we will not understand the basic features of bonobo social structure until they have been studied for many years Dec. 1-4 1. DeWaal, F. Peacemaking Among Primates. Excerpts from Chap. 5, Bonobos, pp. 170-182. 2. Nishida, T. and Hiraigawa-Hasegawa, M. Excerpt from Chimpanzees and bonobos: cooperative relationships among males. In Smuts, B. et al., (eds.) op. cit., pp.172-174 (also review parts of chapter read earlier). XIII. Implications of Nonhuman Primate Behavior for Hominid Evolution Dec. 6 A. Cognitive mechanisms of social behavior As we saw in section III of the course, the evolutionary approach requires us to examine the mechanisms that produce the patterns of behavior out of which social systems are constructed. It also requires us to discover the way we take on the patterns as we develop in the course of our individual lives. The interest in the mechanisms generating adapative behavior in non-human primates, as well as in other animals is probably the oldest one in the evolutionary approach. It was important to Darwin and was central to psychology in the decades around the turn of the century. At that time, animal researchers were concerned with how animals thought. (Kohler's book about chimpanzee problem solving was called "The Mental Life of Apes.") Researchers assumed that adaptive patterns were the product of cognitive processes, that is, processes involved in gathering, remembering and interpreting information. The behaviorist movement (1920-1960) pushed the concern with cognitive mechanisms aside. Animal psychologists turned to studying conditioning and the effects of various nervous system and endocrine system structures on behavior. These studies, which continue today, have contributed to our knowledge of the motivational-emotional mechanisms that generate social behavior. Information about both cognitive and motivational-emotional mechanisms is necessary for understanding the way adaptive behavior patterns are produced. The return of cognition to center stage in psychology was followed by a resurgence of interest in the mental lives of non-humans, especially monkeys and apes. We began to look for cognitive mechanisms that allowed nonhuman primates to participate in complex social systems. Studies, like those described in the chapter by Cheney and Seyfarth, demonstrated that monkeys and apes had a more sophisticated understanding of their social environments than one might expect, given their lack of language. Some primatologists believe that the apparant use of deception by monkeys and apes means that they even have some rudimentary understanding of the mental lives of their fellow creatures as well as of their social relationships. 1. Cheney, D and Seyfarth, R. How Monkeys See the World, Chap. 3, pp. 58-97. Dec. 8 B. Conceptual vs. referential models Tooby and DeVore describe two ways in which information about non- human primate societies can enrich our understanding of the influence of evolution on hominid, and ultimately, specifically human social systems. The referential approach uses existing nonhuman primate species to create a model of what our ancestral hominid species were like and by extension what directive influences evolution has exerted on the development of human social systems. The conceptual approach uses existing nonhuman primate species (and animal species in other orders as well) to generate two classes of theoretical propositions. The first class, socioecological principles, identifies relationships between aspects of social structure and aspects of the setting in which the structure evolves. An example of this would be Wrangham's principle that points to a relationship between the presences of clumped food resources and the development of female bonded societies. The second class, sociobiological principles, identifies relationships between different aspects of social systems. An example of this would be the relationship between mating patterns that promote certainty about paternity and the presence of paternal care. Tooby and DeVore call their particular conceptual model a strategic model because it treats behavior as the product of strategies that have evolved to maintain or increase organisms' reproductive success. This approach, central to modern primatology, is the one we have taken. Part of the chapter (Strategic Modeling) was omitted because it deals with ideas we discussed earlier in the semester. However it can be reviewed as a useful, advanced summary of the approach. Relying on socioecological and sociobiological principles, Tooby and DeVore believe that we can use information about the environment in which hominids originated (the hominid EEA) to generate propositions about the social systems they would have evolved. Information about the hominid EEA specifies the values of the parameters in the socioecological principles. Once the parameters are known, we can enter them into the principles in order to specify some aspects of hominid social sytems. The sociobiological principles can then be used to infer additional features of the social systems entailed by the features specified by socioecological principles. It is hard to disagree with the conceptual approach. The problem, as noted by Wrangham and others, is that we are far from having a body of either socioecologiocal or sociobiological principles that is sufficient to accomplish the goals set out by Tooby and DeVore. The Tooby and DeVore paper is merely an illustration of how a conceptual model might be developed and applied and a critique of existing models, rather that a full description and application of the model. Wrangham's paper is far more modest. It recognizes that no single species of non-human primate can serve as a model for our earliest hominid ancestors. He builds on the paleological principle that features common to many members of closely related species are usually ones that were present in the common ancestor of the species. He calls these an ancestral suite of features. They are ones that have been conserved over the course of evolution and are therefore likely to be basic aspects of the adaptive patterns characterizing a whole family of genera. Wrangham attempts to identify the ancestral suite present in the common ancestors of hominids and apes and therefore likely to be at the core of the adaptative social patterns humans received from their ancestors. While the conceptual and referential approaches differ, they are not incompatible. They should yield overlapping descriptions of the evolved social patterns that were available to our ancestors as they began to be human and enrich their social strategies through reliance on culture. B. Conceptual and referential models 1. Tooby, J. and DeVore, I. Excerpts from The reconstruction of hominid behavioral evolution through strategic modeling. From W.G. Kinzey, (Ed.) The Evolution of Human Behavior: Primate Models, (read the sections within the following sets of page number ranges) pp. 183-190, 200- 202, 207-215, 222-226, 235-237. There is also an optional section, pp. 190-199. Optional Reading 2. Wrangham, R. W., ~African apes: The significance of African apes for reconstructing human social evolution.~ From W.G. Kinzey, (ed.) op. cit. pp. 51-71. Dec. 11 Summary Term Papers are due.
URL: http://www.primate.wisc.edu/pin/syllabi/perloe.html
Page last modified:
February 19, 2002
Maintained by the WPRC Library