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Previc, F. H. (2002). Thyroid hormone production in chimpanzees and humans: implications for the origins of human intelligence. Am J Phys Anthropol, 118(4), 402–3; discussion 404–5.
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Reader, S. M., & Laland, K. N. (2002). Social intelligence, innovation, and enhanced brain size in primates. Proc. Natl. Acad. Sci. U.S.A., 99(7), 4436–4441.
Abstract: Despite considerable current interest in the evolution of intelligence, the intuitively appealing notion that brain volume and “intelligence” are linked remains untested. Here, we use ecologically relevant measures of cognitive ability, the reported incidence of behavioral innovation, social learning, and tool use, to show that brain size and cognitive capacity are indeed correlated. A comparative analysis of 533 instances of innovation, 445 observations of social learning, and 607 episodes of tool use established that social learning, innovation, and tool use frequencies are positively correlated with species' relative and absolute “executive” brain volumes, after controlling for phylogeny and research effort. Moreover, innovation and social learning frequencies covary across species, in conflict with the view that there is an evolutionary tradeoff between reliance on individual experience and social cues. These findings provide an empirical link between behavioral innovation, social learning capacities, and brain size in mammals. The ability to learn from others, invent new behaviors, and use tools may have played pivotal roles in primate brain evolution.
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Santos, L. R., Pearson, H. M., Spaepen, G. M., Tsao, F., & Hauser, M. D. (2006). Probing the limits of tool competence: experiments with two non-tool-using species (Cercopithecus aethiops and Saguinus oedipus). Anim. Cogn., 9(2), 94–109.
Abstract: Non-human animals vary in their ability to make and use tools. The goal of the present study was to further explore what, if anything, differs between tool-users and non-tool-users, and whether these differences lie in the conceptual or motor domain. We tested two species that typically do not use tools-cotton top tamarins (Saguinus oedipus) and vervet monkeys (Cercopithecus aethiops)-on problems that mirrored those designed for prolific tool users such as chimpanzees. We trained subjects on a task in which they could choose one of two canes to obtain an out-of-reach food reward. After training, subjects received several variations on the original task, each designed to examine a specific conceptual aspect of the pulling problem previously studied in other tool-using species. Both species recognized that effective pulling tools must be made of rigid materials. Subsequent conditions revealed significant species differences, with vervets outperforming tamarins across many conditions. Vervets, but not tamarins, had some recognition of the relationship between a tool's orientation and the position of the food reward, the relationship between a tool's trajectory and the substance that it moves on, and that tools must be connected in order to work properly. These results provide further evidence that tool-use may derive from domain-general, rather than domain-specific cognitive capacities that evolved for tool use per se.
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Seyfarth, R. M., & Cheney, D. L. (2002). What are big brains for? Proc. Natl. Acad. Sci. U.S.A., 99(7), 4141–4142.
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Sterling, E. J., & Povinelli, D. J. (1999). Tool use, aye-ayes, and sensorimotor intelligence. Folia Primatol (Basel), 70(1), 8–16.
Abstract: Humans, chimpanzees, capuchins and aye-ayes all display an unusually high degree of encephalization and diverse omnivorous extractive foraging. It has been suggested that the high degree of encephalization in aye-ayes may be the result of their diverse, omnivorous extractive foraging behaviors. In combination with certain forms of tool use, omnivorous extractive foraging has been hypothesized to be linked to higher levels of sensorimotor intelligence (stages 5 or 6). Although free-ranging aye-ayes have not been observed to use tools directly in the context of their extractive foraging activities, they have recently been reported to use lianas as tools in a manner that independently suggests that they may possess stage 5 or 6 sensorimotor intelligence. Although other primate species which display diverse, omnivorous extractive foraging have been tested for sensorimotor intelligence, aye-ayes have not. We report a test of captive aye-ayes' comprehension of tool use in a situation designed to simulate natural conditions. The results support the view that aye-ayes do not achieve stage 6 comprehension of tool use, but rather may use trial-and-error learning to develop tool-use behaviors. Other theories for aye-aye encephalization are considered.
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Van Schaik, C. (2006). Why are some animals so smart? Sci Am, 294(4), 64–71.
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Whiten, A. (2000). Social complexity and social intelligence. In Novartis Foundation Symposium (Vol. 233, pp. 185–96; discussion pp. 196–201).
Abstract: When we talk of the 'nature of intelligence', or any other attribute, we may be referring to its essential structure, or to its place in nature, particularly the function it has evolved to serve. Here I examine both, from the perspective of the evolution of intelligence in primates. Over the last 20 years, the Social (or 'Machiavellian') Intelligence Hypothesis has gained empirical support. Its core claim is that the intelligence of primates is primarily an adaptation to the special complexities of primate social life. In addition to this hypothesis about the function of intellect, a secondary claim is that the very structure of intelligence has been moulded to be 'social' in character, an idea that presents a challenge to orthodox views of intelligence as a general-purpose capacity. I shall outline the principal components of social intelligence and the environment of social complexity it engages with. This raises the question of whether domain specificity is an appropriate characterization of social intelligence and its subcomponents, like theory of mind. As a counter-argument to such specificity I consider the hypothesis that great apes exhibit a cluster of advanced cognitive abilities that rest on a shared capacity for second-order mental representation.
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