Cultural evolution in California and Paris

Studies in History and Philosophy of Biological and Biomedical Sciences xxx (2017) 1e9

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Essay Review

Cultural evolution in California and Parisq Kim Sterelny Australian National University, Australia

The secret of our success, Joseph Henrich pp. xv, 445, Price £22.95, Hardcover Princeton University Press (2016)., ISBN: 9780691166858 How traditions live and die, Olivier Morin pp. xvi, 300, Price £25.99, Paperback Oxford University Press (2016)., ISBN: 9780190210502

1. Competing syntheses? The study of cultural evolution, especially but not only in humans, is a booming cottage industry on the borders of evolutionary biology, archaeology, and biological anthropology, with some additional interference by philosophy, economics, linguistics, and the cognitive sciences. The last few years have seen the publication of an important set of position statements and overviews. This essay is especially focussed on (Henrich, 2016; Morin, 2016b). Of these works, Joseph Henrich’s is much the most ambitious, with wider scope over space and time, loaded with striking examples from archaeology and anthropology (especially anthropology, his home discipline). In developing an account of human uniqueness, it showcases a rich and productive research tradition, combining ethnography, experiment and theoretical modelling. Olivier Morin’s monograph is more limited in its spatial and temporal scope, and in its explanatory agenda. It is much more focussed on largescale, near-contemporary social phenomena, and on the social networks and cognitive capacities that support these phenomena. These two books are important contributions, but (Boyd, 2016; Lewens, 2015; Tomasello, 2014) are also impressive recent position statements. Collectively, these programs are ambitious: they typically aim to explain the distinctive and central features of human social life; some aim as well to explain the striking contrast between the evolutionary trajectory of the hominin lineage and those of our closest living relatives. Humans live just about everywhere and, for

q I apologise for these lame and geographically inaccurate labels to characterise research traditions that originated in the work of, in one case Rob Boyd and Peter Richerson, and on the other, Dan Sperber. I could not think of a better. E-mail address: [email protected].

a large mammal, in huge numbers. Moreover, this is not recent: we have been a numerous and cosmopolitan species for 10,000 years or more. These perspectives all agree that the distinctive character of human social life depends on social or cultural learning, and on the accumulated effects of that learning over space and time. They agree as well that the centrality of cultural learning to human social life makes it appropriate to think of human cultures as evolving systems. However, there seems to be quite significant though often implicit disagreement as well. The conceptual frameworks are often different, as is the identification of the central phenomena to be explained, and characteristic choices of examples. For example, in considering the sender/receiver dynamics of the flow of social information, the “Paris program” emphasises the important role of the background knowledge, interests and capacities of the receiver; the information recipient is not just a passive soak picking up and recording the signal from the source. Arguably in contrast to the Californian program, the Parisians do not think that the flow of social information is well represented as novices copying from models. The debates over adaptationism, gene selection, and multilevel selection have taught us that it is often not easy to distinguish genuine empirical differences from differences in explanatory interests and research heuristics, amongst apparently conflicting views. The main aim of this essay will be to identify these various differences, though I will not entirely resist the temptation to editorialise. I will begin by identifying some common ground, before then delineating differences in explanatory agenda and the differing empirical bets between California and Paris. 2. Common ground: population thinking One central element of the Darwinian toolkit is “populationthinking”: population-based explanations of the change over time. Such explanations depend on the idea that we can often fruitfully represent populations as having the following characteristics: (i) populations consist of autonomous agents interacting in an environment, with those decisions aggregating into causally important features of the population itself; for example, to an equilibrium between different strategies in contexts of conflict; (ii) While members of any natural population will in fact vary in many respects, for some important explanatory projects, much of this variation is irrelevant. Sometimes we can represent the population as just varying in one or a few dimensions. In other cases, we can represent the population as being composed from only a few

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discrete types: males and females; aggressive and conflict-averse agents; predators and prey; sellers and buyers. (iii) While the spatial and temporal distribution of the population may be important, which particular agent is where is rarely or never crucial. Thus these agents are “interchangeable”: the overall trajectory of the population does not depend on the specific decision of any particular individual. In short: there are robust populationlevel patterns, because outcomes depend on the typical results of interactions between the agents, results which depend only on a few of their features. There are many microfoundational pathways through which a population-level pattern can emerge (Elster, 2008). Selective explanations of change in a population over time are obviously population-based explanations in this sense: the increased frequency of lactose tolerance in those human populations with a long history of dairy farming is the aggregate result of many interactions, decisions and outcomes, no one of which was crucial. However, population-thinking is not a feature of evolutionary biology alone. Population-based explanation plays a central role in ecology, in economics and other social sciences. Thus Peter Godfrey-Smith (and in a somewhat different form, Tim Lewens) distinguished three specifically evolutionary versions of population thinking nested within this general category (Godfrey-Smith, 2009; Lewens, 2015). Sperber and his colleagues use this framework both to categorise their own views, and suggest a contrast to the Californians (Claidiere, Scott-Phillips, Sperber, 2014). 1. Evolutionary population-based explanations: the frequency of types at T þ n is largely determined by the frequency at time T. 2. Selective evolutionary population-based explanations: populations are Darwinian populations: with variation, heritability, and differential fitness. Thus the frequency of types at T þ N is importantly determined by selection on those types at previous time steps, with selectively favoured types at one step increasing in frequency at the next in virtue of that success, together with some mechanism supporting resemblance between parent and offspring. 3. A replicator-based evolving population under selection. This is a more specific version of (2), in which heritability depends on replication. On some views this is critical: important forms of evolution (for example, the evolution of complex adaptations) are possible only if the transmission of information from one generation to the next is of high fidelity, and high fidelity depends on replication (Ridley, 2000). In the context of cultural evolution, this would be a framework that represented cultural transmission as the flow of memes from sender to receiver. There is no doubt that both the Parisians and the Californians are committed to some version or versions of population-based thinking. Sperber’s foundational Explaining culture is, amongst much else, a critique of the conception of a culture as a holistic, integrated, totalizing system (Sperber, 1996). His alternative is bottom-up, defending an epidemiological conception of cultures as networks of individual agents in interaction and mutual influence. A key theoretical concept is that of attraction: as agents interact in a public space, swimming through the plankton of public representations, they ignore, filter, transform and sometimes re-express what they encounter, but in ways that are not mostly idiosyncratic. These processes of filtration, transformation and reexpression are shaped by more-or-less common cognitive structures, and by common features of the environment. It is, for example, much easier to retain information if it reaches you in a durable, easily transported, and easily re-used form; like a printed bus timetable that folds into your wallet. Similar considerations influence the reproduction of information. Thus Morin points out

that the reproduction of regular geometric shapes is much more accurate and long-lived than the reproduction of arbitrary doodles: a relatively small set of simple cues fixes the geometric shape, but with a doodle, every feature must be noticed and copied. Moreover, geometric shapes are drawn from a pre-existing repertoire that the experimental subject can already recreate, and these shapes have a simple and unambiguous linguistic specification. They can be represented multi-modally (p30). Likewise, a joke with a truly disgusting punch line is easy to remember. In this framework, environmental and cognitive biases are “factors of attraction1”. The Californians are even more obviously engaged in population-based explanations: their formal models of cultural change are re-engineered from population-genetics into microevolutionary models of cultural change. Their discursive work reinforces this: they repeatedly make the point that the human capacity to cope with challenging environments does not depend alone (perhaps hardly at all) on individual insight and adaptability, but on the population-level process of many agents engaging in some mix of trial and error and social learning, and with the results of this being filtered, summed, and transmitted to succeeding generations. In showing the inadequacy of individual adaptability, they are particularly fond of lost European explorers’ failures to master locals’ reliable survival techniques, and the dismal consequences of those failures. Though all evolutionary hypotheses presuppose populationlevel processes, not all theorizing about cultural evolution is a form of population thinking. Brett Calcott has helpfully distinguished between population explanations and lineage explanations (Calcott, 2008). A lineage explanation of a target phenomenon d say, contemporary human forms of cultural learning d traces a series of incremental steps from an evolutionary baseline (in this case, perhaps great ape social learning capacities) to the target capacity, meeting two conditions. First: adjacent stages differ only in small ways; small enough, so the later stage could be reached by a single change in its predecessor. Second: each stage must be functional, in the presumptive social and physical environment, and adaptively superior to its predecessor, or at least no worse than it. The population-level processes that lever the emergence of each stage are backgrounded. What is foregrounded is the overall structure of the lineage of changes, and the fact that each is a plausible modification of its predecessor. So while a lineage explanation does not make explicit the population level processes necessary for adaptive change, it does make explicit the incremental stages of adaptive change. Lineage explanations are thus closely linked to the other poster form of Darwinian thinking: tree thinking, the representation of a clade and its branching from an ancestral form. A successful lineage explanation is a pathway through a tree. Tomasello’s (2014) is a (partial) lineage explanation of human cooperation and its cognitive prerequisites from a great ape-like basal hominin. Dan Sperber and his colleagues use this analysis of the different forms of population thinking to suggest an important difference between their framework and that of the Californians (Claidiere, Scott-Phillips et al, 2014). They suggest that while their approach should be seen as a version of (1), the Californians propose a version of (2). Sperber and his colleagues argue that “attraction” is not a synonym for “selection”. In part, that is because it is a more general

1 Though the scope of these “factors of attraction” over space and time is highly variable, they cannot be too variable and idiosyncratic without undermining the theoretical motivation of the Paris program: the concept of attraction is theoretically important and tractable only if there are significant, general factors of attraction. That is the point of shifting from specific, historical case studies of the birth and spread of traditions to general, more abstract models of cultural evolution or cultural epidemiology.

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concept. The frequency of a cultural trait can partially predict its own frequency at the next time-step. In their terminology, that is the trait’s homo-impact. But it can also correlate with the frequency of other traits at the next time step: its hetero-impact. Then, in a well-chosen example, they point out that the use of hallucinogens and shamanistic religions positively impact on one another’s frequency and stability: they are mutually reinforcing.2 On this view, formally, selection is a special case of attraction, namely, positive homo-impact. But as they see it, attraction is not just a more general notion: it is a purely statistical notion.3 Having a disgusting punch line is a positive attractor for joke longevity, but that does not (they insist) explain the differential stability of disgusting stories. For an explanation, we need to understand the underlying cognitive and social mechanisms that explain the memorability and conversational impact of such stories. I do not think this distinguishes Paris and California. For though the Californians borrow and adapt their formal models from selectionist evolutionary biology, in important cases, they do not seem to think of selection and fitness in causally robust ways. If selection on a cultural trait genuinely causes its increased frequency, certain questions are inescapable. If one cultural trait is fitter than a variant, who or what benefits and what is the nature of that benefit? One possibility is that it is the bearer of the trait. A culturally acquired trait can certainly increase the biological fitness of its bearer, and can spread differentially to the bearer’s children, but that is only a plausible account of trait fitness for those exceptional cases in which cultural learning is strictly vertical, within the family. Much social transmission is horizontal and oblique. Is the trait itself differentially fitter than its variants? If so, the Californians are saddled with all the intractable problems of memetics. One would have to show that cultural traits themselves form a Darwinian population, and there would have to be some reasonably objective way of counting the individuals, the cultural trait tokens, in the population, of limiting the population’s boundaries, and of identifying ancestor-descendant relationships. To identify the fitness of a given cultural trait token d say, my carrying and expressing Darwinian evolutionary theory d in principle there must be some way of specifying the effects of my manifestation of Darwinism on the evolutionary beliefs of those with whom I have been in contact.4 As Dan Sperber has pointed out, for many cases this looks intractable in theory, not just practice. For we acquire most of our cultural items over multiple exposures from many sources, and our expression likewise becomes just one element amongst many of the experiences of others. There may be no way, even in principle, of telling whether my version of Darwinism, even idealising to the fiction that I carry a single stable version, has “reproduced”, and if so, how often. Social learning is often diffuse. Of course, there are exceptions: the “house style” of lab groups, painting studios with a dominant master, design workshops, artisan/apprentice relationships. But these are exceptions, and the crucial point is that the Californians rarely address these issues. There is a line of argument about evolutionary biology in general that argues that fitness and selection should always be understood statistically rather than causally: to say that one trait is fitter than another, and is under positive selection, is just to say that when we aggregate the many ecological, social and reproductive

interactions within a population, there is a statistical bias in favour of that trait, one that may or may not be robust over variation in environment, time or population structure. I am in general sceptical about this deflationary view of selection,5 but perhaps it captures the way the Californians typically think of fitness: perhaps for them, the fitness of a field of variants is just the aggregated effects of many heterogeneous individual interactions. There is one possible exception: the Californian commitment to cultural group selection. Henrich shares that commitment and defends it in this book, making quite a persuasive case that the differential success of groups could well have been an important factor in the deep history of hominins.6 As he points out (especially in chapter 10), effective inter-group competition does not depend on the view that intergroup violence was typical of forager inter-group relations.7 Intergroup competition could be important through positive selection on groups that had practices that made those groups more productive; better at promoting migration into new or under-exploited territory; less apt to experience physical or cultural extinction in hard times. These are all quite plausible sites of differences between groups, both in the recent history of ethnographic documentation, and in the Pleistocene; when productivity; migration and extinction resistance were all probably important, and probably influenced by norms and other group-level practices (like division of labour). I was less persuaded by his discussion of the PamaNyungan spread. Henrich does indeed argue persuasively that the Pama-Nyungan peoples had an adaptive cultural package: technological, ritual and foraging practices that enabled enough food storage to support periodic large gatherings plus norms that mandated such gatherings; marriage and ritual customs that built horizontal linkages across bands; rituals that were effective in storing important informational resources, and initiation rituals which were intense and protracted, and hence built enduring loyalty between within cohorts that faced initiation together. If all this is true, it is no accident that this cultural complex came to dominate most of Australia. However, there seems little evidence that the mechanism was intergroup competition, rather than diffusion of this cultural package through a group-level version of copy-thesuccessful. For Henrich himself documents, in both Australia and PNG, examples of the wholesale adoption of rituals and norms from neighbouring groups perceived to be successful (again in chapter 10). It is certainly true that once memetics is abandoned, and given the fact that strictly vertical cultural learning is probably the exception rather than the rule (especially if reproductive cooperation evolved early in the hominin lineage), cultural group selection seems to be the most plausible option for a causally robust notion of cultural selection. The Darwinian population is a population of groups (perhaps differentiated genetically; more likely, culturally) that differ in success in part due to their differing cultural profiles. The idea is that groups have characteristic norms, customs, techniques, lore. For individuals within a group are far more networked with, and influenced by, one another than they are by cross-group interactions. These semi-bounded interactions result in local congruence of technique, opinion, norms and habits. Not perfect congruence, and not, of course, with regard to every culturally

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This whole line of argument is reviewed sceptically in (Otsuka, 2016). Though as (Clarke and Heyes, 2016) point out, whether it is important in their deep genetic history depends on whether cultural differences correlate with genetic differences. They do not if, for example, less successful groups are demographically absorbed into their more successful rivals. 7 Sam Bowles and Herbert Gintis defend a view of the evolution of human cooperation that is committed to group selection via tribal conflict, in their (Bowles & Gintis, 2011). I am very sceptical of that analysis (Sterelny, 2016), but those sceptical arguments need not apply to Henrich’s line of thought. 6

2 Other frameworks, of course, just treat hetero-impact as positive or negative coevolution/. 3 Though on this, they are by no means consistent, shifting between quite rich causal and a statistical notion, as (Acerbi & Mesoudi, 2015) show. 4 (El Mouden, Andre et al, 2014) give an account of cultural fitness, but it presupposes that we can independently identify traits and trait tokens.

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influenced phenotypic trait. But enough congruence to make groups relevantly different from one another, and for cultural inheritance to take place from one generation to the next within the group. Fitness, too, is conceptually unproblematic, though it can be specified in two distinct ways. The distinctive cultural profile of a group can be relevant to the group’s demographic productivity: this is multi-level selection one. Or it can be relevant to the group’s propensity to survive crises and/or found new groups: this is multilevel selection two (Okasha, 2006). But while much of the Californian’s discussions of cultural group selection can be mapped on to these well-established modes of group selection, not all can be. Henrich, in particular, counts the diffusion of cultural traits from successful groups to their less successful neighbours (as perhaps in the Pama-Nyungan case above) as a form of cultural group selection, but that is not a version of multi-level selection one or two, and the population is no longer a population of groups (see also (Morin, 2016a; Clarke and Heyes 2017). In sum, then, it seems to me that these frameworks are evolutionary only in a weak sense: the state of the population at one time is very tightly bound by its state at the previous time step, but with the partial exception of some version of cultural group selection, fitness and selection do not play a central causal role in either framework. In contrast, populations and their structure are of central causal importance. Both Morin (in chapter 5) and Henrich (in chapter 12) emphasise the fact that traditions are maintained much more effectively in larger, regularly connected groups, and groups in which these traditions are regularly expressed. 3. What needs explaining? The Californians and the Parisians agree that human cultures are best explained as population-level outcomes: the summed results of biases in individual interactions with each other and with their environment. They agree that models deriving from evolutionary biology can often illuminate the dynamics of these populations, if used with suitable caution. They differ, however, on what is most in need of explanation. For the Californians, it is the informational opacity of the physical and social environment, and human success in coping with that opacity (this is the theme of Henrich’s chapter 7). This success is ancient, prior to the existence of states, industry, science-guided technology. The Californians see the incremental improvement of norms, expertise, information and technology as the factor that sets humans apart from other social learners. Humans have made themselves at home just about everywhere, and we can only have done so by responding successfully to those specific environments, despite the fact that we cannot rely mostly on perceptual mechanisms tuned genetically to their affordances and risks. Fire, shelter and clothes have to be made, and made by transforming materials whose fit-for-function is not manifest to our perceptual systems. Food too, is often not just caught or collected (this is often challenging in itself) with its nutritious character evident from taste and smell. In many traditional, small-scale societies basic foods have to be processed to make them safe and digestible. Henrich, rightly, makes much of this. His poster example is manioc processing. Manioc (cassava) is an excellent starch staple; and the plant is productive in marginal environments. But only if it is purged of cyanide and its derivatives, and detoxification is protracted, laborious (hence short-cuts would be tempting) and the procedure is far from obvious. Manioc is scraped, grated, washed to separate the fibre from the liquid. The liquid is then boiled, and the starch is left to sit for two days before it can be safely baked and eaten. Prior to this procedure, manioc is bitter, and this is perhaps a perceptual cue that eating it is not safe. However, during processing it ceases to be bitter before it is safe. Worse, it is not immediately

and obviously poisonous; the symptoms of poisoning are delayed and chronic, not immediate and fatal. So manioc processing is causally opaque in a very strong sense.8 While the initial taste is probably a signal that it is not safely edible as it stands, it is not a signal that manioc can be made safe; that it is worth being made safe; or of how to make it safe. The opacity of manioc processing is not unique. A similarly complex case is mixing ash (an alkali) with cornflour. This releases niacin, which would be otherwise unavailable. A diet without niacin causes pellagra; a disease which is chronic rather than fatal, but still to be avoided. Here too there is no overt error signal: the cost of error is ambiguous and long-delayed. These are impressive examples of complex competences whose causal structure is hidden even after they have been discovered; an intelligent, sceptical learner might well wander into maladaptive habits. Arguably, though, these examples are not typical, and not characteristic of the adaptive competences of ancient foragers. Manioc contrasts with Lyn Wadley’s discussion of another opaque technology: making an adhesive as part of a compound tool. There, if the glue is not made properly, or if it is dried too fast, the adhesive will crack (or shrink, or fail to bind) and the projectile point will not attach to the haft. It is not obvious in advance what stages are necessary, and how exactly to execute them. But it is obvious, pretty well immediately, in retrospect, if an error has been made (Wadley, 2001, 2010). The example from deep history is important, for Henrich places the origins of cumulative cultural learning deep in the past. He thinks hominin life, and hence hominin evolution, has been profoundly shaped by cultural learning, for perhaps two million years. That seems right to me, but I suspect that it is relatively recently that hominin competences have been (often) retrospectively opaque, not just prospectively opaque. It is very hard to figure out how to knap a handaxe or ignite a fire. But once it is done, one can see what works and what fails. Moreover, in many of these material technology traditions, learning requires understanding the process, not just executing it, to cope with local variations in raw materials. Skilled knappers know their rock; skilled trackers know their animals (Liebenberg, 2013). Cultural learning is ancient, and anciently critical to hominin life. At issue is whether it depends on agents e model and novice e understanding adaptive procedures, rather than merely conforming to them. Obviously, there will be a range of cases. But what is typical, and how has that changed over time? Likewise, the social environment is not informationally transparent. Norms, customs and habits regulate interactions within a community, and these can make the community more, or less, viable as an on-going nexus of economic and reproductive interaction and cooperation. Most of the time, human groups find their way to viable regulative packages, avoiding a Hobbesian state of nature, without (a) actually choosing rules by which to live, and (b) despite actual and potential conflicts of interest within groups. As a consequence, the Californians’ paradigm examples are drawn from small-scale societies, and they are examples of techniques, technologies, norms and taboos that are adaptive for the community in question, but which would be extremely difficult or impossible to invent on the spot. In the best examples, lost explorers demonstrate this difficulty by failing to re-invent the techniques in question, even when their lives depended on it (lovingly detailed in chapter 3). Of course, the Parisians accept that human communities depend on social and technical adaptations to their local circumstances, and that these adaptations are built incrementally, and in ways

8 Matt Spike has pointed put to me that the empirical details of the example are more complex that Henrich’s presentation might suggest, with a variety of methods known; see (Carneiro, 2000).

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mediated by cultural learning. Even though it is probably true that incremental adaptation depends on successive rounds of tinkering, tinkering need not depend on high fidelity, replication-like social learning. That view is controversial, because in his (1999), Michael Tomasello argued that social learning of this kind was essential to cumulative cultural adaptation, and linked fidelity to a specific, supposedly quite demanding form of cultural learning, namely true imitation. Tomasello suggested that human social life, and human minds, are adapted to accumulate skill and information over generations. As a consequence, we all have capacities that no individual could acquire by individual learning alone. In contrast, while animals learn socially, that learning merely enables them to acquire capacities that they could acquire by individual learning, though social learning makes this more rapid or less expensive. Human cultures are unique because only humans systematically exploit the bandwidth and fidelity of true imitation to build adaptive complexes that are (well) beyond the reach of individual, non-social learning. This is so important that human minds have become adapted to cultural and cultural learning. There are two elements to Tomasello’s Ratchet Hypothesis. One is that human social learning (and human social life) is very different from that of other animals because we are able to build on the successes of our predecessors, and as a consequence, we all have capacities that no-one could acquire without extensive social input. As I have noted, this idea is central to the Californian program, and they give many historical examples of invention, innovation and improvement through tinkering. For example, many maritime instruments, like the compass, have lineages of gradual improvement from crude beginnings. The second idea is that building on success depends on a distinctive cognitive capacity, true imitation. True imitation makes high fidelity, one-on-one social learning possible; in particular, it supports the faithful transmission of innovations in technique. The Californians are much more sceptical about this second element of the Ratchet Hypothesis. Much of their work is designed to show that communities can retain and even extend their informational capital without high fidelity one-on-one individual learning. Redundancy compensates for noise. If, for example, a large group of novices select an expert as their model, even if all they learn from the expert is the rough template of a skill, by exploring the space around that template, trying out differing ways of filling it in, perhaps through some lucky errors, a few of those novices will come to match or exceed the expert’s skill level (Henrich & Boyd, 2002). Moreover, Henrich suggests that innovation often depends on individuals combining elements from initially distinct technical traditions: innovation is collective, depending on networked minds (Muthukrishna & Henrich, 2016). Biological, gene-based evolution builds complex adaptations incrementally, and it does indeed depend on high fidelity replication to preserve micro-innovations. But as Morin argues, the differences between genetic and cultural transmission are relevant here: there is nothing in genetic transmission very similar to model choice followed by one-to-many transmission, nor similar to the hybridisation between technical traditions noted by Henrich. So Morin doubts that incremental cultural adaptation is much illuminated by the comparison with incremental biological adaptation (pp 220e222). There is a very important difference in orientation here: the explanation of accumulation is central to the research agenda of the Californians but not to that of the Parisians. Even so, they agree in denying that the community-level accumulation of expertise depends on high fidelity interaction amongst individuals. Perhaps more significantly, the Parisians see the explanatory problem posed by culture somewhat differently. Humans live in, contribute to, and take from a public domain. We swim in a sea of representations. Some representation is overt: gestures, words,

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images. Some is more implicit, for many human cultural products have multiple functions, with sending a signal being only one. Thus personal decoration, clothing styles, modes of interpersonal interaction, the organisation and presentation of houses and their contents, the choice and display of personal property all send messages. But while this public domain is rich, it is mostly ephemeral. Almost everything that is said, depicted, displayed, indicated has a very short shelf life. But amongst this mass, there is a fraction that is picked up by others and re-expressed in the local milieu for a while, and amongst these local successes there is a still smaller fraction that establishes over time and/or space d these are Morin’s traditions. The Parisians see the crucial problem as that of explaining both why there are traditions at all, and of identifying the characteristics d the “factors of attraction” d that explain why a few elements in the public domain become part of enduring traditions.9 If traditions were all and only adaptive but unobvious responses to environmental challenges d how to make fire; how to build a bow and arrow; how to detoxify manioc; how to share food in ways that incentivise effort but protect against bad luck d the Parisians’ core problem would be trivial, with an obvious solution: traditions persist through their utility. They are good tricks, but hard to figure out for yourself, so you remember them and pass them on. But many traditions have no obvious utilitarian value. Songs, folk tales, childhood games and the like can be broadly distributed in space and time. This distribution depended on hundreds or thousands of retellings, without (apparently) keeping anyone alive, fed, or warm. There is almost no overlap between the stock examples of the Californians and the Parisians: their examples are from large-world societies of apparently adaptively neutral folk tales, musical preferences, games. In his 2016, Morin points out that for a cultural item to become a tradition, it must escape two threats. One is wear-and-tear: the cultural item may erode in the passage from one mind to the next. The other is flop: the item arrives safely, but fails to sufficiently stimulate re-expression. The Californians have mostly been concerned with wear-and-tear; the Parisians with flop. That is appropriate given their focus on different cultural phenomena, with their different exemplifications. The utilitarian importance of expertise readily explains why it is expressed, and why novices are motivated to re-acquire it. Its causal opacity explains why mastery is not trivial. Hence the focus on wear-&-tear. The public domain of stories, games and similar cultural product is huge, none of it is life critical, and most of that product dies of neglect. So the key problem is flop, and why a small proportion of that product escapes flop. It is often suggested that human minds are adapted to culture, rather than to any specific environment. The Parisians agree, but only in the sense that our minds are adapted to participate in and navigate through the public domain. In their view, our minds are not adapted to recognise, learn faithfully, and re-express long-lived elements in the public domain. This is a crucial difference d perhaps the crucial difference d between their program and that of most theorists of cultural evolution, who variously think that our minds are adapted to pick up the language, the norms, and the skills of our local communities. The Parisians do not deny that we have some cognitive capacities that support copy-like interactions between agents. We are capable of imitation, and sometimes exercise those capacities (most plausibly in dance, ritual and the like). But they think the importance of these mechanisms is much overstated, and the importance of fidelity-neutral mechanisms much under-stated. Their challenge will be to explain how minds not

9 On the assumption that it is not just chance; that traditions are not just the outliers of a distribution over space and time caused by the stochastic loss of elements in the public domain.

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built for fidelity can nonetheless sustain long-lived, broadly distributed traditions in the right circumstances. The evolutionary project for the Parisians, then, is to explain the emergence of a public domain and the interpretative and communicative capacities that support it, and to show how as a side-effect of those capacities, that public domain over time comes to be populated by a growing number of traditions, some deep and very widespread. As I see it, the Parisian view is both empirical and strategic. Empirically, they argue that cultural learning is typically flexible and reflective (under some form of top-down, voluntary control). It involves intelligent, unencapsulated assessment, both of potential information sources, and of content flowing from those sources10. On the Parisian view, in general social learning is not a form of imitation; especially, it is not a form of quasi-reflex-like copying, not of what most others are doing (it is not conformist); nor from high-prestige models. It is not imitation, because the Parisians take much social learning to be a special case of intentional ostensive communication (Scott-Phillips, 2015). Social sources have informational intentions: they intend to communicate some item to their audience. And that intention is overt: the transfer of information (or misinformation) depends, by design, on the audience’s recognition that the source is communicating. On this conception of communication, communication depends on inference and background knowledge. The source provides clues about his/her informational intention, and the audience uses those clues, together with context and background knowledge, to reconstruct the informational intention. From this framework, three claims follow. (i) Cultural learning through ostensive information is fidelity-neutral. Even if the audience exactly reconstructs the social source’s informational intention, what they then do with that item is up for grabs. In some cases, the audience will endorse and re-express the very same message: the context might be one of religious teaching, with serious penalties for deviance. But there are many other possibilities, for what we do with incoming information, even when it is accurately identified, depends on what else we think and want. (ii) Cultural learning through ostensive intentional communication is not content-neutral. As anyone who has ever lectured undergraduates can attest, the message that the audience reconstructs need not resemble the informational intention. The greater the difference in background knowledge and cognitive skills, the more likely it is that the reconstructed message will differ significantly from the intended message. If the source and audience have a common set of concepts and share appropriate background, and if the informational intention taps into those commonalities, reconstructing the intention can be both accurate and efficient. For example, two birders can communicate the details of an unusual sighting in a word or two. (iii) Cultural learning through ostensive communication is not copying. First, the process of reconstructing and laying into memory the source’s informational intention often involves editing and change; if not at reconstruction then at memory. An audience listens to and understands a story, but only an edited summary of the highlights is absorbed into memory, and when the story is recalled and retold, it may well be embellished and amended in various ways; fitted into story-templates that are already familiar. The girl becomes blonder and dumber; the party more outrageous. These background templates and biases can act as factors of attraction, with homogenising and stabilising effects, making versions of the story more similar than they otherwise

10 Social learning is a highly practiced skill, so, as with driving a car, when all is going as expected, there is no explicit conscious awareness of decision-making, and there are few demands on attention; we are aware of explicit assessment and oversight only in unusual or stressful situations.

would be, and keeping them that way, as they are shoehorned into standard templates. But even when the message sent is the same as the message received and memorised, the cognitive mechanism is not a copying mechanism. That is important, as the same mechanism, in different contexts, would generate variation rather than the continuity of message. In my view, the Parisian view of intentional ostensive communication is over-intellectualised. As they analyse it, it involves complex layers of nested intentions and beliefs. But the more general point that cultural learning is intelligent (rather than reflex-like), chosen and reconstructive seems right, at least for the cases of most central concern to the Parisians: stories, jokes, recipes, discursive verbalised items in the public domain. There are, however, important classes of cases the Parisian picture does not fit. Many regularities that structure human life are not overtly and intentionally communicated: conventions of social distance, turntaking in conversation, how loudly to talk; some aspects of language learning (which looks to be a particularly complex case, involving both imitative and reconstructive processes). There are lots of implicit, unexpressed, untaught norms in social life. This is important, as norms play a central role in the Californian account of the origin and stability of large-scale cooperation so, for them, the mechanisms through which norms establish and spread are of great moment. It is possible that I was once explicitly taught as a child not to spit into other peoples’ soup bowls, but I doubt it. Yet I have clearly learned, and learned socially, not to do so (while anyone is looking). There is a known psychological phenomenon of unconscious imitation, through which agents come to resemble one another in mannerisms, gestural patterns and linguistic habits (Heyes, 2011), and this mechanism (or mechanisms) may well have played an important role in establishing and stabilising many tacit norms, adaptive or not. It is also unlikely that the central examples of the Californian program fit the Parisian model cleanly. Some aspects do apply. Conversation matters in acquiring adaptive competence. For example, in arguing for the importance of endurance hunting in human foraging, Joe Henrich notes that it is necessarily coupled to high class tracking skills, and he documents the importance to tracking of experts sharing information in conversation (pp 75e77). Foragers depend on their technology and technique, but also on their rich data bases of local natural history and geography. We can reasonably assume that much of this is picked up and sustained in conversation. Thus overt intentional communication is important to enduring adaptive traditions, not just the less obviously consequential narrative life of communities. Demonstration, too, is a species of overt communication. Since skills as demonstrated are not the same as skills in use, demonstration depends on the audience realising that the information source is communicating, and is modifying his/her actions in quite distinctive ways. But the informational intention is not that the audience come to recognise a belief or intention in the mind of the source; it is that the audience acquire the skill or capacity demonstrated. So demonstration is not a fidelity-neutral form of social interaction. So the adaptive competence of local communities probably does partially depend on the cognitively rich forms of communication on which the Paris program focuses. But very likely it depends heavily on information leakage and perhaps imitation-like mechanisms as well. Both Henrich and Morin reject the view that there is no teaching in forager (or other small -scale) societies. But the fact that such a view was seriously entertained shows that much cultural learning probably does depend on novices observing skilled activity; on their tagging along with adults as they move through their world; on eavesdropping on expert conversations; on having the opportunities to handle, experiment with, and use equipment made by others, both to practice its use, and to determine how it is

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made. Adult economic activities create informational resources for the incoming generation as their by-product, and these play a central role in the next generation’s re-acquisition of expertise. This is an instance of downstream niche construction,11 a critical element in both the Californian and the Parisian conceptions of culture, though not explicitly discussed by either. 4. Niche construction For Morin, the diffusion of a trait is its distribution in space and time. If we find a trait densely clustered: say, manioc consumption in central America, that diffusion pattern might be the result of transmission, cultural learning from a few innovators. But it could also be the result of convergence: agents responding independently but in parallel to an opportunity. Not all clusters are the result of cultural learning. In fact, the distinction between transmission and convergence names two endpoints in a continuum. Much culturally-mediated human learning is hybrid learning. Agents develop many competences by combining information from their environment and from their social partners. This is a systematic and adaptive feature of human social life; the result of niche construction, typically cumulative niche construction. It is one reason why transmission chain experiments sometimes mis-represent human cultural learning, with designs that exclude cues from the world, abstracting away the environmental context of cultural learning.12 Human communities structure d sometimes directly; sometimes as a by-product of other activities e the developmental environment of the incoming generation. Thus it becomes much more likely that they will acquire some characteristics, and less likely, or outright impossible, that they will acquire others. As a child and adolescent, I had no chance of learning Warlpiri, as I developed in an exclusively English-using environment, as did most of my local peers. Cultural variants persist over generations by indirect influences of this kind. The world of the incoming generation is modified, often cumulatively, in ways that make individual and social cues more effective and more congruent. Everyone in the village grows up amongst the same set of built structures, channelling public and private life the same way; they experience and observe similar daily routines; patterns in third party interaction d who receives deference, who is marginalised; they observe and participate in largely overlapping economic, social and ritual activities. They share as well a largely common physical and biological world, a world that itself has often been shaped by the accumulated effects of their predecessors. Even without teaching or cultural transmission, the shared adult patterns of life tend to reproduce shared patterns of childhood and juvenile experience. This tendency is accentuated to the extent that reproductive cooperation and alloparenting takes place, as this will moderate the effects of parental idiosyncrasies. Even if children learn mostly by experiment and trial and error, with minimal social input, they will tend to learn in similar ways.13 The acquisition of informational capital by the incoming generation is supported by this indirect route of shaping a common environment as well as by the direct route of intergenerational cultural learning, and to the extent that this

11 For a systematic defence of the importance of this process to evolution in general, see (Odling-Smee, Laland et al., 2003). They would treat downstream cumulative niche construction as a special case of what they call ecological inheritance. 12 Not all: Christine Caldwell’s experimental designs with spaghetti towers is an exception, as in many versions subjects can both experiment themselves and observe others’ towers. Some of this work is reviewed in (Caldwell, Atkinson, Renner, 2016). 13 You can learn individually about the social: you can learn about popularity, prestige and power by observing third party interactions.

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indirect route is important, it supports the Parisian view that fidelity-neutral forms of learning are important. The incoming generation learns by exploration plus social cues and clues, rather than by receiving blueprints of parental competences. Morin and Henrich develop this theme of the downstream construction of the environment in which social transmission takes place in different but complementary ways. Morin is focussed on accessibility: on the importance of the shape, size, and connectedness of the social network through which the tradition spreads, and how these factors are shaped by the cumulative history of the group. If connectedness is high, so nodes widely distributed over space and time are linked by short and multiple pathways, the stability of traditions is less dependent on ease and high motivation. The more a tradition approaches the limiting case of Chinese whispers transmission, the more it depends on factors that make it easy and worthwhile to signal; easy to receive; easy to remember. Long, narrow, compact diffusion chains can keep alive only those traditions which are both undemanding to express and learn, and highly salient. Network shape matters, but so too does social and institutional organisation and external scaffolds. When there are few external scaffolds for transmission; and low social investment in transmission, only intrinsically easy to acquire, easy to transmit, information becomes traditional. As the social ecology of the information flow changes, and there is an increasing supply of multiple models, external scaffolds, and social investment in transmission, the bandwidth and character of transmission changes. As the popularity of a practice grows, it becomes more accessible to others, both because it is more salient; everyone knows about it, and because the material infrastructure of the practice becomes ever more readily available (and often cheaper). Thus Morin argues that the familiar S-shape curve supposedly distinctive of social learning take-off can be explained by these facts of accessibility, without appeal to cognitive or motivational conformism. The establishment of a tradition is also self-reinforcing in a second way. The choices of others are not just potential clues to an independent environment (say: the durability and suitability of clothes). They are part of the cost/benefit environment. Choices are also signals. Coordinating with others successfully depends in part on their expectations about how you will behave. If, say, a particular gesture is trending towards general use as a signal for silence on a hunt, each agent acquires a motive to adopt and respond to it. These contextual conditions are very important, and the incoming generation inherits them from their predecessors. Moreover, Morin suggests that these accumulating effects on context give directionality to the deep history of human tradition building. In broadbrush terms, over time, external context has become increasingly favourable to the preservation and accumulation of traditions. The sapiens history of cultural accumulation may well be a result of these changes in external context, rather than internal or intrinsic changes in human cognition (see especially chapter 6). None of these claims about the importance of network size and organisation would be news to Henrich. Much of his own work has been devoted to developing these themes. But in addition, he emphasises a most important phenomenon that Morin neglects: cultural learning is self-reinforcing through inventing tools d physical tools and cognitive tools d that make us better at cultural learning. These too are inherited from the previous generation. This is the theme of the final section of chapter 4. Cultural transmission produces cumulative first order skills, but in addition it builds tools and techniques for transmitting those skills. As Henrich notes: “This is one way cultural transmission increases its own fidelity d learners acquire both the skills themselves as well as techniques for transmitting them” (p52).

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One important difference, though, is the contrasting expectations of the genetic consequences of the increasing contextual support for social learning. On Henrich’s view, as this first and second order information becomes central to hominin lifeways, gradual genetic tweaking would follow. Gene-culture coevolution enhanced first and second order accumulation: enhanced social learning, and learning how to learn socially. I very much agree, but Morin does not. In agreement with Celia Heyes, who pushes these ideas even harder (Heyes, 2012, 2016a, 2016b; Heyes & Frith, 2014), Morin is very sceptical about coevolutionary models of culture and cognition.

5. Modelling minds In the last section 1 raised but left unresolved the question about the extent to which a novice’s use of clues and cues, of leaked information is itself cognitively sophisticated, depending on a nuanced appreciation of the expert’s capacities and the environment’s demands, mediated by the novice’s own developing skill base. A similar question applies to novices’ model choice (and while the Californians downplay the importance of causal knowledge, they often treat model choice as sophisticated). In my view, skill acquisition, especially when genuine, high level expertise is involved, often is cognitively sophisticated. The apprentice acquiring the skill has to engage in targeted practice; in error diagnosis; must assess and address limits in his/her own expertise; exploit informational opportunities in the environment in the forms of advice, templates, imitation, demonstration. Moreover, especially as the apprentice moves towards mastery, advice and other forms of social input must be assessed, not just trustingly accepted. Skill acquisition is hybrid learning. It is learning by doing, but with lots of social input (Sterelny, 2012). Learning by doing typically involves misfires, and this will often require the agent to determine what went wrong and why; to think causally about his/ her interaction with the environment (and there is persuasive evidence that even quite young children naturally engage in causal diagnosis of this kind (Gopnik, 2012)). No doubt many of the skills on which foragers depend require only routine competence rather than high end, long-practiced expertise: detoxifying manioc, recognising plants with hidden tubers, remembering the location of water holes. But archaeology has revealed many examples of forager material culture that seem to display genuine expertise, including examples dating from well before the Holocene (for instance, some of the cave art). Gurven, Kaplan and their colleagues have argued that (male) foragers do not reach peak productivity until well after physical maturity, and if those assessments are generally true of forager cultures, that would strongly suggest that forager intergenerational economics depend on genuine, hardwon, slowly acquired expertise, not routinely acquirable competence (Gurven & Hill, 2009; Kaplan, Hooper, Gurven, 2009). There is a real difference in empirical bets here: the Californians think that a good deal of adaptively relevant information is learned socially through relatively simple heuristics. That is: trust prevailing social opinion d especially if its endorsed by respected senior figures d unless you have strong, clear reasons for disregarding it, even if there are no overt grounds for that opinion. “It’s our custom” is mostly a good enough reason ((Henrich, 2016) p62). The Californians often use one of Henrich’s own examples d a Fijian food taboo that in fact protects pregnant women against a serious disease risk, but whose benefit is by no means well understood by those respecting the taboo d to illustrate both the prevalence and the benefit of this trusting default. But though there is a difference in empirical claim, I think the main difference is with respect to modelling strategies.

The Californians think that it is productive to model social learning as governed by simple trusting defaults, even though in many real circumstances, the cognitive processes are more nuanced. The Californians have developed a family of models of social learning, variously exploring the roles of noisy signals from the environment, group size and connection, redundancy, and model choice. A central theme of this research stream is that communities can identify and accumulate adaptively important information over iterated cycles of transmission from model to novice, without a causal map of the target of their actions, and on the basis of simple learning strategies. For example, in Boyd’s most recent (Boyd, 2016), he discusses a simple model in which agents have to choose between individual and social learning strategies, weighing imperfect information both directly from the world, and from social partners (pp 13e16). The model suggests that agents do well by adopting the local consensus unless the agent has a clear, highly reliable signal directly from the environment. There is no doubt that these models are highly idealised: Morin argues quite persuasively that there is no compelling case that agents really follow semi-automatic conformist heuristics, and he suggests that models should be cognitively realistic (Morin, 2016c). But models always idealise, otherwise they would lose both tractability and generality. There is no comparable body of modelling out of Paris. Indeed, it is not obvious that one could model cultural learning as Paris conceives of it in ways that retain their distinctive view of cultural learning as intelligent, strategic, and dependent on rich theory-of-mind capacities, while still being general and tractable. That would be a problem: in the absence of such models, it is difficult to see the population-level dynamics of the aggregated interactions of strategic, intelligent social learning. There are attempts to confront these modelling challenges (Andre & Morin, 2011; El Mouden, Andre, Morin and D. Nettle, 2014). So suppose the technical problems can be solved. It seems to me that three outcomes are possible. One possibility is that it does not make much difference: populations of trusting social learners, and populations of discriminating social learners, have broadly similar dynamics: similar at the level of resolution offered by comparative ethnographic and archaeological data. A second possibility: cumulative cultural learning might be rare (or even non-existent) in a population of strategic, discriminating cultural learners. As the manioc example might suggest, agents’ confidence in their own judgement might make it more difficult to preserve current levels of cognitive capital reliably enough for it to serve as a foundation on which to build. A high level of social trust might be necessary for cumulative social learning, and the ethnographic and archaeological evidence of cumulative adaptation would then be evidence for trusting social learning in traditional social worlds. A third possibility. Modelling might show that discriminating social learning is a more powerful engine of adaptation and cumulative adaptation than trusting social learning: such a population might generate a richer stock of micro-innovations; identify and take-up such innovations more reliably; weed out errors efficiently. Such models might show that such a population is less apt to be stuck on local optima; to be trapped in inefficient Nash equilibria; to fail in response to environmental change. Does the archaeological and ethnographic record show widespread (though perhaps domain, environment or even culture specific) adaptive failures of the kind we would expect if human populations were populations of trusting social learners? The third possibility suggests a genuine and important empirical difference, but if it is there, it is cryptic without some method of displaying the population level consequences over deep time of the forms of learning the Parisians emphasise. Time to finish. These are both impressive works in themselves, and distinctive examples of their own particular traditions. As noted earlier, Henrich’s monograph is exceptionally ambitious in

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both its empirical breadth and theoretical reach. I have by no means explored all its riches here. In particular, he develops an important set of arguments about social norms and their pivotal role in the evolution of human cooperation. There is a lot to enjoy and to argue with. The scope of Morin’s work is more limited, and it includes a critical, polemical element in its assault on imitation as the key component in human sociality. The rhetoric here is sometimes over-heated. It is more cognitively focussed than Henrich, with a greater interest in cognitive mechanisms. But as with Henrich, there is a rich, contrasting and complementary set of examples, and a nuanced exploration of transmission in different network structures. Both are rewarding, with plenty of insight, and plenty with which to disagree. My copies of both books are now essentially unreadable, with the text buried under annotations, positive and negative.14 References Acerbi, A., & Mesoudi, A. (2015). If we are all cultural Darwinians what’s the fuss about? Clarifying recent disagreements in the field of cultural evolution. Biology and Philosophy, 30, 481e503. Andre, J., & Morin, O. (2011). Questioning the cultural evolution of altruism. Journal of Evolutionary Biology, 24(12), 2531e2542. Bowles, S., & Gintis, H. (2011). A cooperative species: Human reciprocity and its evolution. Princeton: Princeton University Press. Boyd, R. (2016). A different kind of animal: How culture made humans exceptionally adaptable and cooperative. Princeton: Princeton University Press. Calcott, B. (2008). Lineage explanations: Explaining how biological mechanisms change. British Journal for the Philosophy of Science, 60, 51e78. Carneiro, Robert L. (2000). The evolution of the Tipiti: A study in the process of invention. In Gary M. Feinmann, & Linda Manzanilla (Eds.), Cultural evolution: Contemporary viewpoints (pp. 61e94). New York: Springer. Caldwell, C. A., Atkinson, M., & Renner, E. (2016). Experimental approaches to studying cumulative cultural evolution. Current Directions in Psychological Science, 25(3), 191e195. Claidiere, N., Scott-Phillips, T., & Sperber, D. (2014). How Darwinian is cultural evolution? Philosophical Transactions of the Royal Society series B, 369(1642). Clarke, E., & Heyes, C. (2017). The swashbuckling anthropologist: Henrich on the secret of our success (in press) Biology & Philosophy, 32, 1e17 El Mouden, C., Andre, J., Morin, O., & Nettle, D. (2014). Cultural transmission and the evolution of human behaviour: A general approach based on the price equation. Journal of Evolutionary Biology, 27(2), 231e241. Elster, J. (2008). Exploring social behaviour: More nuts and bolts for the social sciences. Cambridge: Cambridge University Press. Godfrey-Smith, P. (2009). Darwinian populations and natural selection. Oxford: Oxford University Press. Gopnik, A. (2012). Science. Scientific thinking in young children: Theoretical advances, empirical research, and policy implications, 337(6102), 1623e1627.

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Gurven, M., & Hill, K. (2009). Why do men hunt?: A reevaluation of “Man the hunter” and the sexual division of labor. Current Anthropology, 50(1), 51e74. Henrich, J. (2016). The secret of our success: How culture is driving human evolution, domesticating our species and making us smarter. Princeton: Princeton University Press. Henrich, J., & Boyd, R. (2002). On modelling cognition and culture: Why cultural evolution does not require replication of representations. Culture and Cognition, 2(87e112). Heyes, C. (2011). Automatic imitation. Psychological Bulletin, 137(3), 463e483. Heyes, C. (2012). Grist and mills: On the cultural origins of cultural learning., 367. Philosophical Transactions of the Royal Society B, 367, 2181e2191. Heyes, C. (2016a). Blackboxing: Social learning strategies and cultural evolution. Philosophical Transactions of the Royal Society: B, 371. Heyes, C. (2016b). Who knows? Metacognitive social learning strategies. Trends in Cognitive Science, 20, 204e213. Heyes, C., & Frith, C. (2014). The cultural evolution of mind reading. Science, 344(6190). Kaplan, H., Hooper, P., & Gurven, M. (2009). The evolutionary and ecological roots of human social organization. Philosophical Transactions of the Royal Society, London, B, 364, 3289e3299. Lewens, T. (2015). Cultural evolution. Oxford: Oxford University Press. Liebenberg, L. (2013). The origin of science: On the evolutionary roots of science and its implications for self-education and citizen science. Capetown, CyberTracker. Morin, O. (2016a). The disunity of cultural group selection. Behavioral and Brain Sciences, 39. Morin, O. (2016b). How traditions live and die. Oxford: Oxford University Press. Morin, O. (2016c). Reasons to be fussy about cultural evolution. Biology & Philosophy, 31(3), 447e458. Muthukrishna, M., & Henrich, J. (2016). Innovation in the collective brain. Philosophical Transactions of the Royal Society series B, 317(1690). Odling-Smee, J., Laland, K., & Feldman, M. (2003). Niche Construction: The Neglected Process in Evolution. Princeton: Princeton University Press. Okasha, S. (2006). Evolution and the units of selection. Oxford: Oxford University Press. Otsuka, J. (2016). A critical review of the statisticalist debate. Biology & Philosophy, 31. Ridley, M. (2000). Mendel’s Demon: Gene justice and the complexity of life. London: Weidenfeld and Nicholson. Scott-Phillips, T. (2015). Speaking our minds. London: Palgrave-Macmillan. Sperber, D. (1996). Explaining culture: A naturalistic approach. Blackwell: Oxford. Sterelny, K. (2012). The evolved apprentice. Cambridge: MIT Press. Sterelny, K. (2016). Cooperation, culture, and conflict. The British Journal for the Philosophy of Science, 67(1), 31e58. Tomasello, M. (2014). A natural history of human thinking. Cambridge: Harvard University Press. Wadley, L. (2001). What is cultural Modernity? A general view and a South African perspective from rose cottage cave. Cambridge Archaeological Journal, 11(2), 201e221. Wadley, L. (2010). Compound-adhesive manufacture as a behavioural proxy for complex cognition in the middle stone age. Current Anthropology, 51(Supplement 1), S111eS119.

14 Thanks to Andrew Buskell, Ellen Clarke, Celia Heyes, Olivier Morin and Matt Spike for their feedback on an earlier version of this essay. Thanks also to the Australian Research Council for their generous grants in support of this research.

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