Susan Hurley's target article is an extraordinary achievement. I cannot judge her contribution from the perspective of philosophers, but she has done those of us working on the empirical sciences side of the topics she reviews a great service by pulling together potentially mutually relevant discoveries and developing specific models of how they might form evolutionary or developmental cascades. Having said this, my three sets of comments are rather along the lines of: “here are yet more empirical findings with which any modelling needs to be consistent.”

1. Imitation and emulation

Hurley presents imitation versus emulation as a clear and straightforward dichotomy, with imitation emerging at a higher level in the shared circuits model (SCM). However, recent analyses in animal social learning studies have dissected emulation into several different categories, some of which overlap with imitation under the general heading of “copying” (Whiten Reference Whiten, Rogers and Williams2006). For example, when a chimpanzee matches whichever of two forms of tool use they see (Whiten et al. Reference Whiten, Horner and de Waal2005a), some level of copying is implicated, and even if the matching to the model is in how the tool moves rather than the bodily actions involved, it is not so clear why this should not be regarded as a form of imitation (copying what the model does with their tool) rather than emulation (copying only the model's effects in the world – how the tool operates). Turning to the empirical evidence, I would argue there is far less direct evidence for emulation in nonhuman animals than Hurley implies. Rather, emulation is often ascribed to an animal as a default explanation when the animal evidences social learning that goes beyond mere stimulus enhancement, but shows little or no imitative fidelity. Positive evidence for emulation is harder to come by. If one sees emulation as learning specifically about the environmental results of actions alone, then one experimental design recently developed becomes particularly significant in this regard. This is the “ghost” experiment in which we discover what observers learn from seeing only an action's environmental effects, which is what an emulation hypothesis suggests they are learning about. In a recent experiment of this kind we obtained the striking result that chimpanzees failed to learn the complex tool technique involved (Hopper et al. Reference Hopper, Spiteri, Lambeth, Schapiro, Horner and Whiten2007), despite having demonstrated earlier that they would copy the particular one of two such techniques they see performed by a chimpanzee (Whiten et al. Reference Whiten, Horner and de Waal2005a). In short, for learning the most complex technologies they can handle, chimpanzees seem to need to see another chimpanzee perform the act. This finding and the handful of other similar “ghost” studies completed with children and nonhuman species (for a review, see Hopper et al. Reference Hopper, Spiteri, Lambeth, Schapiro, Horner and Whiten2007) may have profound significance for the kind of model that Hurley has attempted to build, and more generally for theories of embodied cognition and shared circuits.

2. Imitation and cumulative culture

Hurley embraces the hypothesis that the evolution of imitation was the critical factor enabling the emergence of cumulative culture in our lineage. Some of our recent experimental results question this idea. These concern the first “diffusion” experiments among nonhuman primates. These experiments go beyond the usual dyadic social learning paradigm (“What does B learn from A?”) to examine transmission at the group level, which is what culture requires. It is perhaps surprising that this has not been done before, given that the interest of those conducting the numerous dyadic studies in the literature is often in the functional context of cultural transmission. We have now completed seven such diffusion experiments of various designs (including Chinese whisper “chains” A to B to C, etc., and also “open diffusion,” where a model is introduced into a whole group) with chimpanzees and capuchin monkeys, and in six of these there has been a significant differential spread of the two alternative tool use or foraging techniques we seeded in one founder individual of each group (Bonnie et al. Reference Bonnie, Horner, Whiten and de Waal2007; Dindo et al. Reference Dindo, Thierry and Whiten2007; Hopper et al. Reference Hopper, Spiteri, Lambeth, Schapiro, Horner and Whiten2007; Horner et al. Reference Horner, Whiten, Flynn and de Waal2006; Whiten et al. Reference Whiten, Horner and de Waal2005a; Reference Whiten, Spiteri, Horner, Bonnie, Lambeth, Schapiro and de Waal2007). Thus, whether we describe the process as imitation or emulation, there is sufficient copying fidelity to sustain different traditions. It is therefore not so clear that the brake on cumulative culture in nonhuman primates is lack of copying fidelity. From the completely different perspective of archaeology, Mithen (Reference Mithen, Box and Gibson1999) makes a similar point: Acheulian bifaces were complex enough stone artefacts that there can be little doubt that imitation would have been important in learning the knapping techniques required to make them, yet the technology changed little for a million years. Ergo, imitation was not the magic ingredient needed for cumulative culture.

3. A bigger picture than the SCM

Hurley draws several different cognitive systems into the SCM, such as imitation and theory of mind. In the spirit of seeing what may be a bigger cognitive picture in which these are embedded, I suggest that the relevance of the developmental theories of Leslie and Perner also be considered. Leslie (Reference Leslie1987) first suggested a linkage between the capacity for pretence (a form of simulation) which typically emerges in 18-month-old children and the origins of theory of mind; Perner (Reference Perner1991) in turn went on to develop a more elaborate theory explaining this linkage and a suite of other cognitive capacities including mirror self-recognition, means-ends reasoning, and understanding invisible displacements. His theory explained these in terms of an emerging capacity for “secondary representation,” in which the child becomes able to simultaneously maintain a grasp on primary representations of reality (e.g., “This is a banana; I can see the marble”) and also entertain secondary representations involving different perspectives on this reality (e.g., “I am acting as if the banana is a telephone; you cannot see the marble that I can see”). This is particularly relevant to the attempt to identify developmental and evolutionary cognitive networks and cascades, for Suddendorf and Whiten (Reference Suddendorf and Whiten2001) reviewed extensive evidence that the great apes show a cluster of cognitive attributes with similarities to those analysed by Perner, including the recognition that one is being imitated and the early stages of theory of mind.