Stibbard-Hawkes shows that cultures using material symbols might well not leave traces of that practice in the archaeological record. The paper thus poses an important challenge: When is absence of evidence evidence of absence? This commentary uses behavioural ecology to make modest progress on this problem.

The explanatory model proposed by Sijilmassi et al. appeals to fitness interdependence, and is highly plausible for small-scale societies. We argue that it is less so in the context of the larger societies that much of their empirical evidence is drawn from, and that this is because fitness interdependence does not readily scale up in the way the model requires.

Morin has identified an intriguing puzzle about human communication systems, and one element of the solution: Inscriptional sign systems pose more coordination problems, making sender/receiver coadaptation more difficult. But I reject his view of written language, concluding that inscriptional sign systems can be generalist. The upshot is a cost-based proposal about why generalist ideographic systems are essentially unknown.

The use of ethnography to understand archaeology is both prevalent and controversial. This paper develops an alternative approach, using ethnography to build and test a general theory of forager behaviors, and their variations in different conditions, one which can then be applied even to prehistoric sites differing from contemporary experience. Human behavioral ecology is chosen as the framework theory, and forager social learning as a case study. The argument is then applied to social learning in the late Pleistocene, and hence to a famous archaeological puzzle: the late Pleistocene acceleration of technical innovation and regional differentiation.

Children and subadults were obviously part of ancient human communities, and almost certainly, in important ways their activities were distinctive; they did not routinely act like scaled down adults. Yet their presence was quite cryptic, but not entirely hidden. Their lives and acts did leave traces, although these tend to be be fragile, ambiguous and fast-fading. In addition to pursuing the methodological issues posed by the detection of subadult lives, this special issue raises important questions about the role of children, and their willingness to experiment and play, on innovation. It is true that ethnographically known forager children are almost certainly more autonomous, experimental and adventurous than WEIRD children, and this was probably true of the young foragers of the early Holocene and late Pleistocene too. Their greater willingness to experiment probably fuelled a supply of variation, and perhaps occasionally adaptation as well, especially finding new uses for existing materials. Much more certainly, innovations tend to be noted, taken up and spread by adolescents. They were vectors of change, even if perhaps only rarely initiators of change.

We argue that Stanford's picture of the evolution of externalised norms is plausible mostly because of the idealisations implicit in his defence of it. Once we take into account plausible amounts of normative disagreement, plausible amounts of error and misunderstanding, and the knock-on consequences of shunning, it is plausible that Stanford under-counts the costs of externalisation.

Debates on the contingency of history have largely focused on the history of life. This article targets the supposed contingency of human history. It does not defend a global claim about the overall contingency of history. Rather, it aims to identify and explain the difference between robust and fragile historical trajectories. It does so by considering a set of contrasting cases and identifying critical differences among the cases. The analysis shows that one important source of contingency is the historical emergence of command-and-control institutions; one important source of robustness is the existence of population-level processes structured by relatively stable institutions.

The term ‘neolithization’ as it is generally used in relation to southwest Asia narrows the focus of research, and works against our efforts to envision explanations of the process in terms of the long-term evolution of human societies. Here, we re-frame the neolithization process, setting it within the framework of niche construction theory. We argue that the concept of cultural niche construction fits the purpose, but needs to be extended to encompass the more complex social worlds of the Holocene in the form of the cognitive-cultural niche.

We would like to begin by thanking the commentators for their thoughtful, informed and, for the most part, generous responses. Even Ofer Bar-Yosef, while clearly disagreeing deeply with our whole approach, has invested precious resources of time and thought in our paper. We shall respond commentary by commentary, but there are some common themes in the responses, and we will note those as we go through.

This article has both substantive and methodological goals. Methodologically, it shows that rational choice theory (in its behavioral ecology form) is an especially important tool for guiding research in contexts in which agents appear to be acting against their best interests. The Neolithic transition is one such case, and the article develops a substantive conception of that transition, illustrating the heuristic power of behavioral ecology.

Brian Skyrms's Signals has the virtues familiar from his Evolution of the Social Contract (1996) and The Stag Hunt (2003). He begins with a very simple model of agents in interaction, and in a series of brief and beautifully clear chapters, this model and its successors are explored, elaborated, connected and illustrated through biological theory and the social sciences. Signals borrows its core model from David Lewis: it is Lewis's signalling game. In this game, two agents interact. One agent can observe which of two equi-probable states the world is in, but that agent cannot act directly and profitably on that information. However, the informed agent can act in a way that will be perceptually salient to a second agent: say, by raising a red or a green flag. The second agent does have the capacity to respond appropriately to each state of the world. If that second agent chooses the right option, given the state of the world, both are rewarded. If the second agent fails to choose the right action, neither are. Obviously, the two agents are best off if they have a practice in which the informed agent regularly chooses a distinct, salient cue in response to each of the two world states, and in which the powerful agent uses that cue to select the rewarding act. Less obviously, agents with simple trial and error learning capacities can learn to signal and respond: neither explicit negotiation nor cognitive sophistication are required. Likewise, if individual agents do not have the capacity to learn, but if they breed true but with some variation, the evolutionary version of trial and error learning can take a population to one of the signalling system equilibria.

Those familiar with Paul Churchland's earlier work will expect A Neuro-computational Perspective to be lively, provocative and interesting. They will not be disappointed. Churchland is best known for his sceptical view of belief-desire psychology. He suspects this theory is hopelessly false. This welcome collection of his essays includes this work but also his papers on the subjective aspects of the mind and his more recent adventures in philosophy of science. Three themes unify the collection: an anti-sententialist view of cognition, an emphasis on the plasticity of the human mind and a strong endorsement of connectionist models of human cognitive processes.