Tomasello, Michael. The Cultural Origins of Human Cognition. Cambridge, MA: Harvard University Press, 2000. vi + 248 pp. $29.95.
Michael Tomasello is well known for his research on the social and cultural skills of both human children and great apes. This has given him a unique cross-species perspective and an excellent background for constructing a theory of human cognitive evolution, because some of the best evidence in this field is comparative in nature. Living apes, especially chimpanzees, are typically used as models or surrogates for our Miocene ape-like ancestors, whom they resemble in many ways. By comparing us to them, we can try to specify what aspects of cognitive function changed, as ancient primates evolved first into hominids, and then into humans.
Early in his book, Tomasello points out that apes and humans are as genetically close as horses and zebras, or lions and tigers. But the latter are not much different in their cognitive skills, certainly not to the degree that humans and apes diverge. This fact needs explaining. The human cognitive-cultural universe, with its languages, symbols, and technologies, often seems just as far removed from the minds of our closest relatives as it is from the minds of much more distant ones, such as dogs or dolphins. Moreover, this difference evolved very fast and followed a somewhat independent time-trajectory from brain expansion, which also needs explaining. The archaeological record shows a significant increase in the size of the hominid brain about two million years ago, and another about half a million years ago, when the rate of change accelerated dramatically, leveling off about one hundred thousand years ago. But hominid skill did not always improve in step with brain expansion. The refinement of human skills, as shown for instance in tool making and fire tending, seems to have occurred at its own pace, without any concurrent change in brain volume. Most of the more dramatic improvements in human tool making, such as those of the late Upper Paleolithic, occurred long after the hominids had achieved modern encephalization ratios.
This argues strongly that brain evolution alone cannot explain these archaic cognitive achievements. There must have been another factor at work. Tomasello believes that new factor was cultural transmission itself. Any improvement in the ability to accumulate and transfer knowledge across generations would have enabled hominid cultures to innovate and to retain those innovations. As hominid culture grew in complexity, its influence on cognition would have increased, through its impact on infant development. Gradually, human cognition became increasingly tethered to cultural evolution.
But this logic still leads us back to the brain. Cultural skills must depend on a specific brain adaptation of some kind. Apes have a very limited capacity for communication, and almost no intentional expressive skills, and this could not have changed without appropriate changes to the nervous system. What was the nature of those changes? The usual (glib) answer is language. Hominids evolved language, and this enabled them to construct cultures. But this begs the question. What is language, exactly? What were its antecedents? What specific adaptations to the primate brain made such a radical innovation possible? What fundamental changes enabled the hominid brain to acquire a vocabulary of 100,000 words, produce unlimited numbers of novel utterances, and register millions of verbal memories?
Tomasello's answer is a subtle one. He acknowledges that we need a cognitive theory of cultural origins, which is a common, indeed obvious conclusion. But he also realizes that we need a cultural theory of cognitive origins, which is a less common, and much less obvious position. The title of his book draws our attention to the cultural origins of cognition, not vice-versa. He is telling us that it is not enough simply to proclaim that language is the building-block of human culture, assuming that language capacity somehow evolved in its own right, ahead of culture, and then triggered a cultural revolution. Our best evidence contradicts this idea. The human brain does not seem to have an identifiable "language module." Broca's and Wernicke's regions have homologues in the brains of chimpanzees, and even in those of rhesus monkeys. The blueprint of the human brain resembles the primate brain in virtually every important aspect but size. Moreover, language acquisition depends closely on certain aspects of social development. It does not self-install in a brain that is socially disconnected in infancy. Rather, its growth is tied closely to the development of social cognition. Recent developmental research has made this point in a particularly elegant manner. Because of their inability to enter the intersubjective world of culture, children who are deficient in this respect, such as autistic children, show deficits in language acquisition that are proportional to their social disconnection.
This has evolutionary implications, because it suggests that the basics of social cognition must have evolved before language capacity. Language could not have evolved ahead of culture. Rather, certain aspects of social cognition must have come first. Social cognition is logically prior because it provides the communicative "platform" for language. Tomasello has tried to specify these aspects of social cognition in some detail. In his view, the critical capacities hang on the evolution of an improved ability to "take perspectives" on the mental states of others. This is sometimes called "mind-reading" ability, or having a "theory of mind." He also suggests that there is a second critical capacity for the spontaneous combustion of expressive culture, the sharing of attention. Once we had the ability to share attention and have a theory of mind, the rudiments of cultural transmission would presumably have been in place.
This theory has much in common with the work of other developmental theorists in this field, notably Katherine Nelson, who has written extensively on the evolutionary implications of developmental research. The uniqueness of Tomasello's contribution lies in his thorough and up-to-date review of recent research on intentionality and cognitive collaboration and his detailed theory of the mechanisms that interlink a child's mind with culture. In my opinion, his analysis adds substantially to this field. Tomasello is a staunch continuity theorist; that is, he rejects evolutionary miracles and looks for a smooth blending from ape to human characteristics. He finds the roots of essential human social skills such as joint attention in existing primate attentional skills such as gaze following. Similarly, he sees the origins of cultural learning by imitation in the emulative skills of chimpanzees and the origins of pedagogy in the capacity of primates to profit from social facilitation. His gradualist approach is also applied elsewhere: the primate talent for object manipulation evolved gradually into human tool making, and primate social signals combined with improved mind-reading skills and became symbolic. Thus, the leap to language no longer appears to involve a qualitative break-through, or saltation, and its evolution becomes much less mysterious than it appeared in the context of neo-Chomskyan theory, which suggested that human language was completely different from its primate antecedents.
Tomasello has made a convincing case for the generative role of social cognition in language evolution. But I think he has left some important things out of his evolutionary hypothesis. I do not dispute the critical importance of social understanding. But we cannot ignore the motor aspect of communication and representation. Improved social under standing could not have led to language in itself. Without a major modification of their motor capacities, primates would have been good social observers who were still unable to formulate complex expressions. The primate brain also had to evolve the high-level motor control processes that support imitation, phonation, and complex hierarchies of language-related skills.
Tomasello has shown that human expression has deep roots in social cognition and that the signature trademarks of the human mind, language and symbolic thought, could not have evolved without a special talent for social cognition. In doing this, he has given us a unique perspective on joint attention, imitation, collaboration, and mind reading. His message is that we will never understand how the brain generates language until we understand the neural basis of social understanding. I couldn't agree more. But I would add a caveat: don't underestimate the motor side of the equation. This having been said, Tomasello's short, readable, and highly accessible volume is essential reading for clinicians and neuroscientists interested in human evolution, social cognition, language, or disorders of communication.
Merlin Donald, F.R.S.C.
Department of Psychology; Queen's University; Kingston, Ontario K7L 3N6