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decades. Worldwide, there are at other group members, individuals least nine different populations Primer of social can potentially based on song differences. In the gain from others’ knowledge of a North Pacific, there are distinct range of costs and benefits that are Northeast and Northwest Pacific associated with place, including song types. Some of these whales local level of predation risk, locations are able to hear each other’s songs Richard W. Byrne of optimal feeding sites, and what in the central Pacific where more is edible there. Note that these than one song can be recorded in The term ‘imitation’ has a range gains come automatically from the same area. It is unclear whether of meanings in everyday usage behavioural matching, not as a result using different song types in and no single agreed definition in of knowledge transfer. the central Pacific breed with each science. In biology, imitation has Behavioural synchrony is in other, but animals in the western usually referred to morphological fact reported in a wide range of and eastern North Pacific do not adaptations for camouflage or social animals, and extends to a use the song of the other population mimicking the appearance of another detailed level of activity copying, and concurrent recordings of both species (Figure 1). Only recently such as preening together [1], or types in the central Pacific are not has there been intense interest the nearly simultaneous turning very common. It remains to be seen in the imitation of behaviour by of each individual in a flying flock whether some blue whales in the animals; animal has of shorebirds that generates such central Pacific have learned to use traditionally ignored imitation. One spectacular aerial acrobatics. both song types or whether animals purpose of this Primer is to help In some instances, the adaptive just keep the song identified from explain why researchers do now care function of behaviour matching is their population for life. Given the about animal imitation; another is less obvious. Contagious yawning distribution of blue whales and the to chart the various kinds of action is found in as well as geographic and temporal variation imitation that may be important for humans, and the synchrony appears of song types, it appears that vocal biology and illustrate the sometimes to involve arousal level as well as learning does not come into play. confusing array of terms that have overt activity: one possibility is As in many cases with animals that been coined to describe them. that synchronization of sleeping is cannot be studied in the laboratory, Among the variety of definitions of adaptive, or was in human ancestry. further data are needed to draw such ‘imitate’ found in English dictionaries, Human yawning is also contagious to conclusions with confidence. three quite distinct senses are dogs, but it is not yet known whether generally apparent. All three have dogs affect each other in this way: Where can I find out more? biological equivalents in the adaptive in a long-domesticated species, the Discovery of Sound in the Sea http://www.dosits. functions served by animal imitation, function may instead relate to how org/ Janik, V.M. (2005). Acoustic communication and I shall use these as a structure dogs mesh with human behaviour. networks in marine . In Animal to understand what cognitive Cognitively, imitation that Communication Networks, P.K. McGregor, ed. mechanisms are required for the produces immediate behavioural (Cambridge: Cambridge University Press), pp. 390–415. different forms of imitation. synchrony requires an individual to Noad, M.J., Cato, D.H., Bryden, M.M., Jenner, recognize specific actions in others’ M.N., and Jenner, K.C.S. (2001). Cultural revolution in whale song. Nature 408, 537. Aiming to resemble behaviour that are already in its own Oleson, E.M., Calambokidis, J., Burgess, W.C., One objective of imitation in repertoire. This sort of copying may McDonald, M.A., LeDuc, C.A., and Hildebrand, everyday life is to resemble as be understood simply as response J.A. (2007). Behavioral context of call production by eastern North Pacific blue closely as possible the individual facilitation, where seeing an action whales. Mar. Ecol. Prog. Ser. 330, 269–284. whose behaviour is copied, usually ‘primes’ the individual to do the same Payne, K., and Payne, R. (1985). Large scale because their behaviour is judged to [2,3]. No special mechanisms are changes over 19 years in songs of humpback whales in Bermuda. Z. Tierpsychol. 68, 89–114. be admirable or because the imitator required to understand performance Smith, J.N., Goldizen, A.W., Dunlop, R.A., and wishes to be seen as like them in of the action, as no new behaviour is Noad, M.J. (2008). Songs of male humpback some key ways (“imitation is the added to the individual’s repertoire. whales, Megaptera novaeangliae, are involved in intersexual interactions. Anim. Behav. 76, sincerest form of flattery”). There 467–477. are several circumstances in which Conveying a social message Stafford, K.M., Nieukirk, S.L., and Fox, C.G. (2001). Geographic and seasonal variation of blue animal imitation of this sort might be A different kind of imitation is when whale calls in the North Pacific. J. Cetacean adaptive; most are cases where the the copying itself conveys a social Res. Manage. 3, 65–76. imitation is immediate and the result signal. Postural , in which Suzuki, R., Buck, J.R., and Tyack, P.L. (2006). entropy of humpback whale songs. is behavioural synchrony. two people who like or love each J. Acoust. Soc. Am. 119, 1849–1866. Predators are thought to target other quite unconsciously adopt Tyack, P.L., and Clark, C.W. (2000). Communication individuals that stand out in some the same or a mirror image of body and acoustic of dolphins and whales. In Hearing by Whales and Dolphins, W.W.L. way, so behaving just like other posture has long been noted by Au, A.N. Popper, and R.R. Fay, eds. (New York: members of a flock or herd may social psychologists. Very young, Springer Verlag), pp. 156–224. reduce risk. A general tendency even new-born infants copy the to match the current actions of facial gestures of adults interacting others, when in a group, might with them, for instance smiling or Sea Research Unit, School of Biology, University of St Andrews, Fife therefore be expected to evolve tongue-protrusion [4]. This ‘neonatal KY16 8LB, UK. in social species. Moreover, by imitation’ may increase maternal E-mail: [email protected] copying the current behaviour of investment in the child by signalling Current Biology Vol 19 No 3 R112

People also use mimicry to mock to members of other communities or deride others, as in the cruel in a way that is disturbingly human. mimicry of schoolchildren and in However, there is no indication that sophisticated satire. The capacity to intercommunity violence is predicated derive pleasure from manipulating on non-conformity, arguing against the feelings of others implies a rich such a rich interpretation. understanding of mental states The cognitive mechanism of [5]. Intriguingly, chimpanzees at imitation when used as a social the Burger’s Zoo, Arnhem, have signal is likely to vary with the actions been seen to imitate the limp of a copied and the motivation to do so [2]. disabled group member. However, Where the actions are ‘transparent’, wild chimpanzees at several sites that is, they look much the same suffer high frequencies of disability from the perspective of mimic and from snare injuries, yet no similar model, then priming or facilitation mimicry has ever been noted. of specific actions may be all that is Rather than enjoying cruelty, it may required, as in the previous category. be that the Arnhem chimpanzees With neonatal imitation, however, the were influenced by a general action copied is wholly opaque and tendency to behavioural synchrony any explanation will require an innate and the suffering of the mimicked system that matches observed facial individual was incidental; ascribing gestures with the motor commands understanding of complex mental needed to imitate them. It is difficult states may be unwarranted. to determine how extensive a set of In all these cases, any social correspondences might exist, when message conveyed is an immediate the neonate has such a limited motor one, but humans also show a sort repertoire; theorists range from those of imitation when they converge on who attribute hard-wired matching the behavioural norms of their social of just a few key facial gestures to group, conveying the message of those who posit in the infant the group membership — and conversely, ability to match 1:1 the complete out-group exclusion. Conformity to motor repertoire [4]. Where lasting group norms of behaviour has long consistency is seen, a tendency to been studied in . conform is additionally required. This In chimpanzees and , a general can override what has been learnt Figure 1. Sombre bee orchid (Ophrys fusca). tendency to conform to the actions from individual ; and the Imitation is widespread in biology, but usually of the majority of the group has bias to social learning is frequency- the copy results from morphological adapta- also been reported and described dependent, more potent if more tion. The flower of each Ophrys orchid spe- as conformity. Individuals that individuals are showing the same cies imitates the appearance and pheromo- have already discovered how to actions. nal signal of a particular species of insect, open a puzzle box satisfactorily resulting in copulation attempts that serve (chimpanzees), or found a food that Following the example to pollinate its flowers. Imitation of actions is less well understood. is palatable (rats), switched to the Learning how to do something actions and choices of the majority. from seeing it done might seem the In these experiments conformity most obvious sense of imitation, alert awareness and cognitive was valueless, but the behaviour yet scientific interpretations of it competence, and has also been may be a by-product of a trait that have varied from a cheap described in chimpanzees. Adult functions in reducing exposure to trick to an exalted pinnacle of humans use imitation of actions to risk in unpredictable environments. animal . Even now, it is signal that a social connection has Certainly, both chimpanzees and rats unclear which species of animal been made, for instance returning have been noted as conservative have the ability to learn by imitation. a wave. Many greeting signals in behaviour, for instance being Partly this relates to semantic and ceremonies of animals might remarkably cautious about trying confusion, between learning by be thought of as imitation of this novel foods. A similar explanation imitation and learning that follows kind, but since these actions are may apply to the short-lasting ‘fads’ from imitation. As we have noted stereotyped they may simply be shown by young gorillas, such as already, the tendency to copy the evoked by the social circumstances. the once-popular habit of pushing actions of nearby conspecifics Although monkeys have been through the legs of researchers rather occurs widely among animals and described as unable to imitate, when than walking around them. Finding can be straightforwardly explained their actions are instantly copied behavioural conformity among our in most cases as a result of priming by human experimenters they react closest relatives, the great , those responses that match actions strikingly, suggesting signalling it is tempting to presume that its seen. Where animals are engaged in social connection by imitating is function might relate to a sense of instrumental activity, this behaviour- part of the natural communicative group identity, as in humans. Male matching tendency may result in a repertoire of monkeys. chimpanzees certainly show violence naïve individual applying actions that Magazine R113 are in fact appropriate to the task sooner than it otherwise might. If that brings success the animal will often learn to use these actions again. A tendency to copy — whether described as imitation, response facilitation or priming — can therefore accelerate learning, and indeed such benefits may have contributed to the evolution of response facilitation in some species. But the learning itself is consequent on getting a favourable result: reinforced trial-and-error learning, in behaviourist jargon. Most experimental tests of animal imitation can be explained in this way, because the experimenters presented the task immediately after the subjects had observed a skilled performer, with rewards contingent on success. Learning by imitation can be shown by introducing a delay before testing, as has been done successfully with both quail and budgerigars. In these cases, the animal evidently learnt to link an action in its repertoire — for example, pulling, pecking or stepping — with a particular task, by seeing it used. This has been described as contextual imitation, because what the animal learns is when and where to apply an existing behavioural tactic in its repertoire [2]. The Holy Grail of animal imitation studies, however, is to discover a species that is capable of learning a new skill by observation. Another species, that is: there is no doubt that humans can learn in this way, even though in western cultures it is now more common to acquire new skills with some form of verbal instruction. Examples of human skills that seem particularly dependent Figure 2. A mountain gorilla deals with a spiny thistle. on learning by imitation are sushi- The elaborate food-processing skills of great apes depend on natural abilities, including indi- making, blacksmithing, and stone- vidual digit control, bimanual coordination, and a tendency to explore and play with objects. working by medieval masons. In a But imitation of the organizational structure or ‘gist’ of the process used by skilled adults al- more mundane context, most of us lows efficient guidance of learning, and the learned manual skills of apes are uniquely complex have watched an expert take apart among non-humans. a machine — perhaps a mechanic helping us fix our automobile — and part or outline of the task to be put way her mother operates on objects, come away knowing, however together from observation before ever as she has smaller hands and less imperfectly, how to do it ourselves trying it out. strength: precise copying of every next time. This kind of imitation, called Cognitively, the requirements action would be maladaptive. production-imitation, involves an for imitating a good example are Moreover, the potential benefits of individual constructing a behavioural quite different to those cases learning by imitation vary with task routine new to it, out of components where the function is to resemble difficulty: where complexity is low, in its pre-existing repertoire, from another individual or give out a purely individual learning is to be watching a more expert model [2,6]. social message [6]. Fine detail is expected, avoiding the costs of Of course, it is unlikely that an entirely unimportant as long as the right finding and watching a skilled model. novel task will be mastered in a single result is obtained, and indeed it is It is therefore in learning the most viewing without practice or relevant likely that details are better acquired technically complex and involved prior experience; but crucially, by individual experience. A child, for tasks that imitation should pay. production- imitation allows some instance, cannot copy the precise Complex skills cannot be assembled Current Biology Vol 19 No 3 R114

in a single attempt, so we should imitation in animals comes from the way the infant is able to compute expect acquisition to be hierarchical, technically complex achievements that forehead is only needed progressively building up larger of the great apes (Figure 2). because hands are occupied, and and larger components. That is Chimpanzees in northern Congo can therefore be ignored. Something true whatever learning mechanism regularly make two different types similar to this ‘rational imitation’ is involved, but if the gist of the of tool in advance of arriving at sites has been seen in chimpanzees, right approach can be discerned by where subterranean termites can be presented with a demonstration imitation, learning can progress found. A sturdy rod is used to punch of how to get food from a puzzle by organizational leaps rather than a hole deep enough to reach the box [11]. When the box is opaque, by plodding acquisition of actions termites, then a more delicate probe the apes copy both actions used in sequence. is used to agitate the termites, which by the experimenter; but when it is of the organizational gist of a task bite onto the stem and can thus transparent, thus revealing that the has been termed ‘program-level be fished out [7]. Rwandan gorillas first action makes no contact with imitation’ [6]. regularly process a local species of the food, they ignore it. Program-level imitation is nicely stinging nettle: stripping up stems It is not yet clear whether illustrated when a child copies a to detach the leaves, twisting off chimpanzees will indeed prove to word she has not heard before. The the petioles, sometimes repeating show rational cause-and-effect child’s sound is typically quite both these steps several times to understanding of what they imitate, different to that of the adult model, accumulate a larger handful, then or whether simpler explanations such with much higher-pitched vowels pulling up the leaf-bundle and folding as behaviour parsing will suffice. But and often systematic simplification it over the thumb, finally re-grasping a recurring theme in this article has of consonant clusters. This shows the package before ingestion. been the intriguing behaviour of great that what is copied is the program- In both and gorilla apes (and occasionally cetaceans), level gist of the word, a new way to examples, the actions used at each that has repeatedly led researchers assemble the motor programs for processing stage are highly specific, to suspect cognitively complex producing vowels and consonants — and it is very improbable that each explanations. In contrast, imitation which are already in the child’s single individual could invent the of actions is widespread and repertoire. Crucially, this process of appropriate process without some biologically important among other synthesis depends on prior analysis information from an expert model. taxa, but the cognitive mechanism that parses the adult’s sound into its Great apes that live with people of these cases is relatively component units. Compare this with copy human actions, sometimes straightforward to understand. the same word imitated by a myna remarkably complex ones. One : the resulting sound pattern is orangutan was noted pushing References so close to the human model that glowing embers together, fanning 1. Hoppitt, W., Blackburn, L., and Laland, K.N. (2007). Response facilitation in the domestic it can be hard to tell them apart the embers with a flat plate, fowl. Anim. Behav. 73, 229–238. spectrographically. Because the decanting kerosene into a container 2. Byrne, R.W. (2002). Imitation of novel complex vocal apparatus of the bird is quite and putting it on glowing embers — actions: What does the evidence from animals mean? Adv. Stud. Behav. 31, 77–105. different, a double syrinx rather than fortunately, not completely efficiently 3. Laland, K.N. (2008). Animal cultures. Curr. Biol. a single larynx, it is clear that the bird or the jungle camp might have burnt 18, R366–R370. matches the audible result rather down [8]. 4. Meltzoff, A.N. and Prinz, W. eds. (2002). The Imitative Mind: Development, Evolution, than the organization of behaviour. In all these cases, the individuals and Brain Bases. (Cambridge: Cambridge Copying of results rather than concerned had prolonged opportunity University Press). actions, termed emulation learning, for casual observation of skilled 5. Frith, C., and Frith, U. (2005). Theory of mind. Curr. Biol. 15, R655–R645. has sometimes been considered models, and their imitative ability 6. Byrne, R.W., and Russon, A. (1998). Learning ‘simpler’ for animals than imitation can be explained by a perceptual by imitation: a hierarchical approach. Behav. Brain Sci. 21, 667–721. and assumed to underlie animal process, behaviour parsing, which 7. Sanz, C.M., and Morgan, D.B. (2007). behaviour that appears imitative. detects the statistical regularities of Chimpanzee tool technology in the Goualougo The evidence from child psychology, complex but repeated behaviour [9]. Triangle, Republic of Congo. J. Hum. Evol. 52, 420–433. however, suggests the reverse Imitation by behaviour parsing 8. Russon, A.E., and Galdikas, B.M.F. (1993). when it comes to practical tasks is presumably part of the human Imitation in free-ranging rehabilitant with objects: extensive evidence repertoire, too, but human children orangutans (Pongo pygmaeus). J. Comp. Psychol. 107, 147–161. exists for early child imitation, but go beyond this relatively unselective 9. Byrne, R.W. (2003). Imitation as behaviour none for effective emulation prior to process when they imitate. Eighteen- parsing. Phil. Trans. R. Soc. Lond. B 358, 4–5 years. This perspective makes month-old infants, when shown how 529–536. 10. Gergely, G., Bekkering, H., and Király, I. (2002). especially remarkable some of the to turn on a light by an adult who Rational imitation in preverbal infants. Nature emulation noted in cetaceans: for leans forward to press the switch 415, 755. 11. Horner, V., and Whiten, A. (2005). Causal instance, a calf with their forehead, often copy the knowledge and imitation/emulation switching in an aquarium, teased by a visitor whole performance — even though in chimpanzees (Pan troglodytes) and children blowing smoke at the glass, went to they could use a hand more easily. (Homo sapiens). Anim. Cogn. 8, 164–181. its mother to suck milk, then returned But when researchers modified the to the visitor and blew a cloud of milk task so that the adult was holding Scottish Research Group, and Centre for Social Learning and Cognitive towards him, like smoke! a cloak around their shoulders, Evolution, School of Psychology, University Unsurprisingly, the strongest infants never copied the use of the of St. Andrews, Fife KY16 9JP, Scotland, UK. evidence for program-level forehead [10]. Apparently, in some E-mail: [email protected]