Tomasello begins Chapter 2 with the distinction that drives the entire book: the distinction between biological and cultural inheritance. In fact, he states the hypothesis of the book in two sentences just a few paragraphs in to Ch. 2:
My particular claim is that in the cognitive realm the biological inheritance of humans is very much like that of other primates. There is just one major difference, and that is the fact that human beings "identify" with conspecifics more deeply than do other primates. (p. 14)To argue for this thesis, he has to answer two questions, which he gives on p. 15:
- How does the cognition of primates differ from that of other mammals?
- How does the cognition of humans differ from other primates?
So what can most mammals do, cognitively? Tomasello gives two lists, the first general and the second social (p. 16-17). I'll just discuss one, because he doesn't explain it very well. On the first list (non-social cognitive abilities), he includes the ability to pass object permanence tests. What is an object permanence test? It's just what it sounds like. It's a test to determine if an individual (human or nonhuman) understands the basic properties of solid objects, which include numerosity (most things don't spontaneously multiply themselves), motion, and permanence (things don't just disappear). Here are some examples of classic Piegetian object permanence tests (from this paper):
These were obviously designed for children. In a typical experiment, the child, often a very young infant, will be shown several different versions, some of which an individual would expect if she understood the properties of solid objects, and some of which she wouldn't. Experimenters determine whether the child understands these properties by measuring how surprised the child is when a particular event occurs (often by measuring looking time or sucking, both of which will increase if the child sees something novel or unexpected). For example, in the top two sets of drawings above, an object (in this case, a toy train) starts out in plain view, and then disappears behind a larger solid object (the rock). If the train does not come out the other side, then the child should expect the object to still be behind the rock when it is lifted. If the train has come into view on the other side of the rock, the child should be surprised to see a train when the rock is lifted. Thus, if a child looks longer in the second case than in the first, we can infer that the child understands that particular aspect of object permanence. Human infants understand this from a very, very young age, and other mammals appear to understand it as well.
Back to Tomasello. After listing many similarities between primates and other mammals, he singles out one particular difference: the ability of primates to understand relational categories, particularly in the form of "third-party social relationships" (p. 17). While most mammals are able to understand kinship and dominance relationships between themselves and other individuals, primates are able to understand kinship and dominance relationships between two other individuals, and to use this knowledge in interacting with those individuals. Primates, unlike other mammals, are also able to understand relational categories in non-social domains, though as Tomasello notes, they must be extensively trained to do so. In essence, you could say that primates, but not other mammals, developed a concept of "same" in the social realm, and with extensive training, they can extend this concept to non-social domains. For example, if you give a dog two objects, one of which is larger than the other, and reward it for picking the larger object, it will eventually pick the larger object all of the time. If you then substitute the first two objects for two different objects of different sizes than the first, one of which is larger than the other, the dog will not know to pick the larger object until it has been trained to pick that specific object. It doesn't understand that the two pairs of objects involve the same relationship: one is bigger than the other. Chimps, on the other hand, can be trained to do this, though it takes a while. Human children, on the other hand, do this early in development and without any training.
This is where Tomasello draws the line between primate cognition and the cognition of other mammals. He then begins to draw the line between human and primate cognition. The first difference he notes is human understanding of causation. And it is this understanding that allows humans to attribute beliefs and goals to other humans. Only after gaining the ability to represent causal relations between two events (rather than simply associating the two events) can we understand that an individual's beliefs or goals caused him or her to act in a certain way. Interestingly, just as Tomasello believes that primate understanding of relational categories in non-social domains is an extension of their understanding of such categories in social domains, he believes that human understanding of causal relations in general arose from our understanding of mental causation.
I have to admit, I'm doubtful about that. Whereas chimpanzees have a very difficult time extending their social understanding of relational categories to physical relational categories, human infants appear to develop a concept of causation independently of the development of theory of mind. While there isn't much evidence for a "causation" module in the human brain, infants do begin to develop an increasingly complex concept of causation beginning at about six months of age, which is long before most of our theory of mind capabilities begin to emerge (check out this book chapter for a great review of the literature on infant causal knowledge). If our causal knowledge were dependent on our knowledge of mental causation, we would expect the latter to develop before, or at least simultaneously with causal knowledge.
But I'm digressing again. From page 26 on, Tomasello discusses primate culture. By this time, you've probably realized that "culture" is a pretty loaded word. Many anthropologists and biologists use it to refer to something like the following1:
[B]ehavioral patterns that diffuse across a group of individuals through some form of social learning and is subsequently displayed by a significant membership of the group. (p. 55)Tomasello, on the other hand, reserves the term for cumulative culture that is achieved through imitative learning and direct teaching. And this is where we further see the dividing line between humans and nonhuman primates.
If we use the first definition of culture, then many nonhuman species can be said to display cultural cognition. Chimps, bonobos, macaques, and even dolphins and whales (as Clark notes) can develop behavioral patterns, ranging from tool use to courtship rituals, that are specific to particular isolated groups, and which are learned by young by observing adults (see this paper for a nice review of different types of cultural behaviors, in the broader sense, in chimps). But Tomasello argues that these aren't instances of what he refers to as culture, because they are not transmitted through teaching and imitation. Instead, they are transmitted through emulation learning and ontogenetic ritualization. Both of these, he notes, require a great deal of intelligence, but neither constitutes true cultural transmission.
Here is the example that Tomasello gives of emulation learning:
If a mother rolls a log and eats the insects underneath, her child will very likely follow suit. This is simply because the child learned from the mother's act that there are insects under the log -- a fact she did not know and very likely would not have discovered on her own. But she did not learn from her mother how to roll a log or to eat insects: these are things she already knew how to do or could learn how to do on her own. (p. 29)The distinction between emulation learning and true imitation is very important. As Tomasello notes, there have been few, if any, observed cases of nonhuman primate parents (specifically mothers) teaching behaviors to their children. Instead, the mother performs a behavior with her child nearby, the child observes the end result (in the example above, the exposing of food), and repeats the act not because it's what the mother did, but because it understands the affordances of the objects involved, and uses that understanding to achieve the same end result that its mother did. This requires a very complex understanding of affordances, which, in the words of Norman Donald, are:
[T]he perceived and actual properties of the thing, primarily those fundamental properties that determine just how the thing could possibly be used. A chair affords ("is for") support, and, therefore, affords sitting. (p. 9)It is through the complex understanding of the affordances of objects that nonhuman primates are able to innovatively develop tools. In order to use a stick to retrieve termites from a mound by placing it into holes in the mound, a chimpanzee must understand that a stick of a certain size will fit into holes of a certain size, for example. But because chimpanzees are not learning to use tools from their conspecifics through imitation, but rather through emulation learning, their ability to develop and use tools is highly limited. This is reflected in the differences between human and nonhuman primate tool use, which Marc Hauser and Laurie Santos list in the following table2:
Notice that both nonhuman primates and humans are able to recognize the "relevant design features" and use "multiple materials for different tools." Both of these require understanding the affordances of objects, but little else. However, the rest of the abilities on the list, which only humans exhibit, require more than this. They require an understanding of causation (for developing tools that consist of "parts with different functions," for example), the ability to build upon existing uses of a tool (cumulative culture), and most likely, the ability to learn the use of a tool through something more than the mere association of an event and an outcome that is involved in emulation learning. If you only learn an association between an event (e.g., rolling a log or putting a stick in a termite mound) and an outcome (getting food, e.g.), it will be much more difficult for you to use the object or action to achieve other, perhaps unrelated outcomes.
The second type of social learning that Tomasello attributes to chimps is ontogenetic ritualization (p. 31-33). He describes this type of learning in the context of gestural communication. Nonhuman primates develop group-specific, or even individual-specific gestural signals through a process in which one or more individuals comes to associate a particular gesture with a particular outcome. Once again, this type of learning does not require imitation or an understanding of the goals of the gesturer/observer. Thus he writes
[Emulation] learning and ontogenetic ritualization are precisely the kinds of social learning one would expect of organisms that are very intelligent and quick to learn, but that do not understand others as intentional agents with whom they can align themselves. (p. 33)Tomasello argues that emulation learning and ontogenetic ritualization can explain all of the group-specific behaviors observed in several primate species. While he doesn't address the issue, because he is more concerned with our closest evolutionary ancestors, these types of learning might also explain what many see as cultural learning in other mammal species, such as whales and dolphins. For an example, in an article linked by Clark in a post on Chapter 1, researchers report observing orcas develop a unique technique for capturing gulls. Once one whale started using this technique, the rest of the whales in the tank picked it up and began using it successfully as well. This sort of learning is consistent with other examples of cultural transmission (in the broader sense) observed in toothed whales (see this paper for more examples). But at this point, there's no reason to think that the orcas were learning through imitation rather than emulation in which they observed a behavior and an outcome they desired, and thus emulated the behavior to achieve the same outcome. It may turn out that orcas, unlike nonhuman primates, are able to learn through imitation, which might present an interesting case of convergent evolution (and wouldn't affect Tomasello's arguments directly), but at this point there doesn't appear to be any reason to believe that's the case.
At the end of the section on primate culture in Chapter 2, Tomasello feels that the evidence overwhelmingly indicates that chimpanzees are not able to transmit information culturally (in his sense of the word), and that this is because they are not able to understand others as intentional agents. Thus, he feels he's answered both of the questions I quoted at the beginning of this post, and that the answers support his hypothesis. In the next post on Chapter 2 (which will be much shorter, I promise), I'll talk about his discussion of human culture. Hopefully by the end of Chapter 2, everyone will have a good understanding of just where Tomasello is going, and why.
1 Sinha, A. (2005). Not in their genes: Phenotypic flexibility, behavioural traditions cultural evolution in wild bonnet macaques.Journal of Biosciences, 30(1), 51-64.
2 Table 1 (p.20) in Hauser, M.D., & Santos, L.R. (In Press). The evolutionary ancestry of our knowledge of tools: From percepts to concepts.