Primate Cognition

Ludwig Wittgenstein remarked that if lions could speak we would not understand them. David Premack (1986), following this conceptual thread, commented that if chickens had syntax they would have nothing much to say. The first comment raises a methodological challenge, the second a conceptual one. Studies of primate cognition have faced both.

For some, monkeys and apes appear much smarter than nonprimates. If so, why might this be the case? One dominant perspective suggests that social life has exerted extraordinary pressure on brain structure and function, and has led to a mind that is capable of tracking dynamically changing social relationships and political struggles (Byrne and Whiten 1988; Cheney and Seyfarth 1990; Humphrey 1976; Povinelli 1993). In primates -- but few other species -- individuals form coalitions to outcompete others, and following aggressive attack, subordinates often reconcile their differences with a dominant, engaging in exceptional acts of kindness and trust such as kissing and testicle holding (de Waal 1996; Harcourt and de Waal 1992). Such behavior, along with apparent acts of deception (Hauser 1996), has provided the foundation for experimental investigations of underlying cognitive mechanisms. Here, I tackle three problems so as to shed light on the architecture of the primate mind: (1) IMITATION, (2) abstract CONCEPTS, and (3) mental state attribution.

Imitation In some monkey species, all chimpanzee populations, and one orangutan population -- but in no gorilla populations -- individuals use tools to gain access to food (Matsuzawa and Yamakoshi 1996; McGrew 1992; Visalberghi and Fragaszy 1991). The observation that individuals within a population ultimately acquire the same tool-using technique has been taken as evidence that primates are capable of imitation. There are, however, several paradoxical findings and controversies over the interpretation of these observations (Heyes and Galef 1996; Tomasello and Call 1997; Byrne and Russon forthcoming). First, in some study populations, young require 5-10 years before they master tool technology. Although some of this can be accounted for by maturational issues associated with motor control, one would expect faster acquisition if imitation, or a more effective teaching system, was in place (Caro and Hauser 1992). Second, most experiments conducted in the lab have failed to provide evidence that naturally reared monkeys and apes can imitate (Whiten and Ham 1992), although a recent set of studies on chimpanzees and marmosets suggest that some of the previous failures may be due to methodological problems rather than conceptual ones (Heyes and Galef 1996). Third, and perhaps most paradoxical of all, apes reared by humans can imitate human actions (reviewed in Tomasello and Call 1997). This suggests that the ape mind has been designed for imitation, but requires a special environment for its emancipation -- a conceptual puzzle that has yet to be resolved (see SOCIAL COGNITION IN ANIMALS).

Abstract Concept In several primates, the number of food calls produced is positively correlated with the amount of food discovered (reviewed in Hauser 1996). In chimpanzees, a group from one community will kill a lone individual from another community, but will avoid others if there are two or more individuals. Are such assessments based on an abstract conceptual system, akin to our number system? Recent experiments, using different experimental procedures, reveal that both apes and monkeys have quite exceptional numerical skills (reviewed in Gallistel 1990; Hauser and Carey forthcoming). Thus, chimpanzees who have learned arabic numbers understand the primary principles of a count system (e.g., one-one mapping, item indifference, cardinality) and can count up to and label nine items (Boysen 1996; Matsuzawa 1996). Using the violation of expectancy procedure designed for human infants, studies of rhesus monkeys and cotton-top tamarins have revealed that they can spontaneously carry out simple arithmetical calculations, such as addition and subtraction (Hauser and Carey forthcoming; Hauser, MacNeilage, and Ware 1996). Although nonhuman primates will never join the intellectual ranks of our mathematical elite, they clearly have access to an abstract number concept, in addition to other abstract concepts (e.g., transitivity, color names, sameness, cause-effect, identity, kinship) that contribute to the intricacies of their social life. And primates are probably not even unique within the animal kingdom in terms of such conceptual capacities, as other species have demonstrated comparable cognitive prowess (see review in Thompson 1995).

Mental State Attribution Are primates intuitive psychologists in that they can reflect upon their own beliefs and desires and understand that others may or may not share such mental states? Consider the following observation: a low-ranking male chimpanzee who is about to mate sees a more dominant male approaching. The low-ranking male covers his erect penis as the dominant walks by. This kind of interaction -- and there are thousands of observations like this in the literature -- suggests a capacity for intentional deception (see MACHIAVELLIAN INTELLIGENCE HYPOTHESIS). If true, the following capacities must be in place: the ability to represent one's own beliefs and desires, the ability to understand perspective, and the ability to attribute intentions to others. The evidence for each of these capacities is weak, at best, but the experimental research program is only in its infancy. Studies using mirrors suggest that all of the apes, and at least one monkey (cotton-top tamarins), respond to their reflection as if they see themselves, rather than a conspecific (Gallup 1970; Hauser et al. 1995; Povinelli et al. 1993). Self-recognition can be computed by perceptual mechanisms alone, whereas self-awareness implies some access to one's own beliefs and desires, how they can change, and how they might differ from those of another individual. The mirror test is blind to issues of awareness.

Many animals, primates included, follow the direction of eye gaze. However, current evidence suggests that neither monkeys nor apes understand that seeing provides a window into knowledge. A suite of experiments now show that monkeys and apes do not use eye gaze to infer what other individuals know, and thus do not alter their behavior as a function of differences in knowledge (Cheney and Seyfarth 1990; Povinelli and Eddy 1996). Given that this capacity emerges in the developing child well before the capacity to attribute intentional states to others and that perspective taking plays such a critical role in mental state attribution, it seems unlikely that primates have access to a theory of mind. But we should withhold final judgment until additional experiments have been conducted.

The human primate once held hands with a nonhuman primate ancestor. But this phylogenetic coupling happened 5-6 million years ago, ample time for fundamental differences to have emerged in the human branch of the tree. Nonetheless, many features of the primate mind have been left unchanged, including some capacity for imitation and some capacity to represent abstract concepts. The future lies in uncovering the kinds of selective pressures that led to changes in and conservation of the general architecture of the primate mind.

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-- Marc D. Hauser

References

Boysen, S. T. (1996). "More is less": The distribution of rule-governed resource distribution in chimpanzees. In A. E. Russon, K. A. Bard, and S. T. Parker, Eds., Reaching into Thought: The Minds of the Great Apes. Cambridge: Cambridge University Press, pp. 177-189.

Byrne, R. W., and A. Russon. (Forthcoming). Learning by imitation: A hierarchical approach. Behavioral and Brain Sciences.

Byrne, R. W., and A. Whiten. (1988). Machiavellian Intelligence: Social Expertise and the Evolution of Intellect in Monkeys, Apes and Humans. Oxford: Oxford University Press.

Caro, T. M., and M. D. Hauser. (1992). Is there teaching in nonhuman animals? Quarterly Review of Biology 67:151-174.

Cheney, D. L., and R. M. Seyfarth. (1990). How Monkeys See the World: Inside the Mind of Another Species. Chicago: University of Chicago Press.

de Waal, F. B. M. (1996). Good Natured. Cambridge, MA: Harvard University Press.

Gallistel, C. R. (1990). The Organization of Learning. Cambridge, MA: MIT Press.

Gallup, G. G., Jr. (1970). Chimpanzees: Self-recognition. Science 167:86-87.

Harcourt, A. H., and F. B. M. de Waal. (1992). Coalitions and Alliances in Humans and Other Animals. Oxford: Oxford University Press.

Hauser, M. D. (1996). The Evolution of Communication. Cambridge, MA: MIT Press.

Hauser, M. D., and S. Carey. (1998). Building a cognitive creature from a set of primitives: Evolutionary and developmental insights. In D. Cummins and C. Allen, Eds., The Evolution of Mind. Oxford: Oxford University Press, pp. 51-106.

Hauser, M. D., J. Kralik, C. Botto, M. Garrett, and J. Oser. (1995). Self-recognition in primates: Phylogeny and the salience of species-typical traits. Proceedings of the National Academy of Sciences 92:10811-10814.

Hauser, M. D., P. MacNeilage, and M. Ware. (1996). Numerical representations in primates. Proceedings of the National Academy of Sciences 93:1514-1517.

Heyes, C. M., and B. G. Galef. (1996). Social Learning and Imitation in Animals. Cambridge: Cambridge University Press.

Humphrey, N. K. (1976). The social function of intellect. In P. P. G. Bateson and R. A. Hinde, Eds., Growing Points in Ethology. Cambridge: Cambridge University Press, pp. 303-321.

Matsuzawa, T. (1996). Chimpanzee intelligence in nature and in captivity: Isomorphism of symbol use and tool use. In W. C. McGrew, L. F. Nishida, and T. Nishida, Eds., Great Ape Societies. Cambridge: Cambridge University Press, pp. 196-209.

Matsuzawa. T., and G. Yamakoshi. (1996). Comparision of chimpanzee material culture between Bossou and Nimba, West Africa. In A. E. Russon, K. A. Bard, and S. T. Parker, Eds., Reaching into Thought: The Mind of the Great Apes. Cambridge: Cambridge University Press.

McGrew, W. C. (1992). Chimpanzee Material Culture. Cambridge: Cambridge University Press.

Povinelli, D. J. (1993). Reconstructing the evolution of mind. American Psychologist 48:493-509.

Povinelli, D. J., and T. J. Eddy. (1996). What young chimpanzees know about seeing. Monographs of the Society for Research in Child Development 247.

Povinelli, D. J., A. B. Rulf, K. R. Landau, and D. T. Bierschwale. (1993). Self-recognition in chimpanzees (Pan troglodytes): Distribution, ontogeny and patterns of emergence. Journal of Comparative Psychology 107:347-372.

Premack, D. (1986). Gavagai! or the Future History of the Animal Language Controversy. Cambridge, MA: MIT Press.

Thompson, R. K. R. (1995). Natural and relational concepts in animals. In H. L. Roitblat and J. A. Meyer, Eds., Comparative Approaches to Cognitive Science. Cambridge, MA: MIT Press, pp. 175-224.

Tomasello, M., and J. Call. (1997). Primate Cognition. Oxford: Oxford University Press.

Visalberghi, E., and D. Fragaszy. (1991). Do monkeys ape? In S. T. Parker and K. R. Gibson, Eds., "Language" and Intelligence in Monkeys and Apes. Cambridge: Cambridge University Press, pp. 247-273.

Visalberghi, E., and L. Limongelli. (1996). Acting and understanding: Tool use revisited through the minds of capuchin monkeys. In A. E. Russon, K. A. Bard, and S. T. Parker, Eds., Reaching into Thought: The Minds of the Great Apes. Cambridge: Cambridge University Press, pp. 57-79.

Whiten, A., and R. Ham. (1992). On the nature and evolution of imitation in the animal kingdom: Reappraisal of a century of research. In P. J. B. Slater, J. S. Rosenblatt, C. Beer, and M. Milinski, Eds., Advances in the Study of Behavior. New York: Academic Press, pp. 239-283.

Primate Cognition

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