A model for tool-use traditions in primates: implications for the coevolution of culture and cognition

Inspired by the demonstration that tool-use variants among wild chimpanzees and orangutans qualify as traditions (or cultures), we developed a formal model to predict the incidence of these acquired specializations among wild primates and to examine the evolution of their underlying abilities. We assumed that the acquisition of the skill by an individual in a social unit is crucially controlled by three main factors, namely probability of innovation, probability of socially biased learning, and the prevailing social conditions (sociability, or number of potential experts at close proximity). The model reconfirms the restriction of customary tool use in wild primates to the most intelligent radiation, great apes; the greater incidence of tool use in more sociable populations of orangutans and chimpanzees; and tendencies toward tool manufacture among the most sociable monkeys. However, it also indicates that sociable gregariousness is far more likely to produce the maintenance of invented skills in a population than solitary life, where the mother is the only accessible expert. We therefore used the model to explore the evolution of the three key parameters. The most likely evolutionary scenario is that where complex skills contribute to fitness, sociability and/or the capacity for socially biased learning increase, whereas innovative abilities (i.e., intelligence) follow indirectly. We suggest that the evolution of high intelligence will often be a byproduct of selection on abilities for socially biased learning that are needed to acquire important skills, and hence that high intelligence should be most common in sociable rather than solitary organisms. Evidence for increased sociability during hominin evolution is consistent with this new hypothesis.     

Evolution of social learning does not explain the origin of human cumulative culture

Because culture requires transmission of information between individuals, thinking about the origin of culture has mainly focused on the genetic evolution of abilities for social learning. Current theory considers how social learning affects the adaptiveness of a single cultural trait, yet human culture consists of the accumulation of very many traits. Here we introduce a new modeling strategy that tracks the adaptive value of many cultural traits, showing that genetic evolution favors only limited social learning owing to the accumulation of maladaptive as well as adaptive culture. We further show that culture can be adaptive, and refined social learning can evolve, if individuals can identify and discard maladaptive culture. This suggests that the evolution of such "adaptive filtering" mechanisms may have been crucial for the birth of human culture.     

Transmission fidelity is the key to the build-up of cumulative culture

Many animals have socially transmitted behavioural traditions, but human culture appears unique in that it is cumulative, i.e. human cultural traits increase in diversity and complexity over time. It is often suggested that high-fidelity cultural transmission is necessary for cumulative culture to occur through refinement, a process known as 'ratcheting', but this hypothesis has never been formally evaluated. We discuss processes of information transmission and loss of traits from a cognitive viewpoint alongside other cultural processes of novel invention (generation of entirely new traits), modification (refinement of existing traits) and combination (bringing together two established traits to generate a new trait). We develop a simple cultural transmission model that does not assume major evolutionary changes (e.g. in brain architecture) and show that small changes in the fidelity with which information is passed between individuals can lead to cumulative culture. In comparison, modification and combination have a lesser influence on, and novel invention appears unimportant to, the ratcheting process. Our findings support the idea that high-fidelity transmission is the key driver of human cumulative culture, and that progress in cumulative culture depends more on trait combination than novel invention or trait modification.     

Grist and mills: on the cultural origins of cultural learning

Cumulative cultural evolution is what 'makes us odd'; our capacity to learn facts and techniques from others, and to refine them over generations, plays a major role in making human minds and lives radically different from those of other animals. In this article, I discuss cognitive processes that are known collectively as 'cultural learning' because they enable cumulative cultural evolution. These cognitive processes include reading, social learning, imitation, teaching, social motivation and theory of mind. Taking the first of these three types of cultural learning as examples, I ask whether and to what extent these cognitive processes have been adapted genetically or culturally to enable cumulative cultural evolution. I find that recent empirical work in comparative psychology, developmental psychology and cognitive neuroscience provides surprisingly little evidence of genetic adaptation, and ample evidence of cultural adaptation. This raises the possibility that it is not only 'grist' but also 'mills' that are culturally inherited; through social interaction in the course of development, we not only acquire facts about the world and how to deal with it (grist), we also build the cognitive processes that make 'fact inheritance' possible (mills).     

The swashbuckling anthropologist: Henrich on The Secret of Our Success

In The Secret of Our Success, Joseph Henrich claims that human beings are unique—different from all other animals—because we engage in cumulative cultural evolution. It is the technological and social products of cumulative cultural evolution, not the intrinsic rationality or ‘smartness’ of individual humans, that enable us to live in a huge range of different habitats, and to dominate most of the creatures who share those habitats with us. We are sympathetic to this general view, the latest expression of the ‘California school’s’ view of cultural evolution, and impressed by the lively and interesting way that Henrich handles evidence from anthropology, economics, and many fields of biology. However, because we think it is time for cultural evolutionists to get down to details, this essay review raises questions about Henrich’s analysis of both the cognitive processes and the selection processes that contribute to cumulative cultural evolution. In the former case, we argue that cultural evolutionists need to make more extensive use of cognitive science, and to consider the evidence that mechanisms of cultural learning are products as well as processes of cultural evolution. In the latter case, we ask whether the California school is really serious about selection, or whether it is offering a merely ‘kinetic’ view of cultural evolution, and, assuming the former, outline four potential models of cultural selection that it would be helpful to distinguish more clearly.     

Cultural transmission and biological markets

Active cultural transmission of fitness-enhancing behavior (sometimes called “teaching”) can be seen as a costly strategy: one for which its evolutionary stability poses a Darwinian puzzle. In this article, we offer a biological market model of cultural transmission that substitutes or complements existing kin selection-based proposals for the evolution of cultural capacities. We demonstrate how a biological market can account for the evolution of teaching when individual learners are the exclusive focus of social learning (such as in a fast-changing environment). We also show how this biological market can affect the dynamics of cumulative culture. The model works best when it is difficult to have access to the observation of the behavior without the help of the actor. However, in contrast to previous non-mathematical hypotheses for the evolution of teaching, we show how teaching evolves, even when innovations are insufficiently opaque and therefore vulnerable to acquisition by emulators via inadvertent transmission. Furthermore, teaching in a biological market is an important precondition for enhancing individual learning abilities.     

ON OPTIMAL LEARNING SCHEDULES AND THE MARGINAL VALUE OF CUMULATIVE CULTURAL EVOLUTION

The age‐dependent choice between expressing individual learning (IL) or social learning (SL) affects cumulative cultural evolution. A learning schedule in which SL precedes IL is supportive of cumulative culture because the amount of nongenetically encoded adaptive information acquired by previous generations can be absorbed by an individual and augmented. Devoting time and energy to learning, however, reduces the resources available for other life‐history components. Learning schedules and life history thus coevolve. Here, we analyze a model where individuals may have up to three distinct life stages: “infants” using IL or oblique SL, “juveniles” implementing IL or horizontal SL, and adults obtaining material resources with learned information. We study the dynamic allocation of IL and SL within life stages and how this coevolves with the length of the learning stages. Although no learning may be evolutionary stable, we find conditions where cumulative cultural evolution can be selected for. In that case, the evolutionary stable learning schedule causes individuals to use oblique SL during infancy and a mixture between IL and horizontal SL when juvenile. We also find that the selected pattern of oblique SL increases the amount of information in the population, but horizontal SL does not do so.     

Should dispersers be fast learners? Modeling the role of cognition in dispersal syndromes

Both cognitive abilities and dispersal tendencies can vary strongly between individuals. Since cognitive abilities may help dealing with unknown circumstances, it is conceivable that dispersers may rely more heavily on learning abilities than residents. However, cognitive abilities are costly and leaving a familiar place might result in losing the advantage of having learned to deal with local conditions. Thus, individuals which invested in learning to cope with local conditions may be better off staying at their natal place. In order to disentangle the complex relationship between dispersal and learning abilities, we implemented individual‐based simulations. By allowing for developmental plasticity, individuals could either become a ''resident'' or ''dispersal'' cognitive phenotype. The model showed that in general residents have higher learning abilities than dispersers. Dispersers evolve higher learning ability than residents when dispersers have long life spans and when dispersal occurs either early or late in life, thereby maximizing the time in one habitat patch. Time is crucial here, because the longer an individual resides in a location where it can use its learned knowledge or behavior, the more often it profits from it and thus eventually obtains a net benefit from its investment into learning. Both, longevity and the timing of dispersal within lifecycles determine the time individuals have to recoup that investment and thus crucially influence this correlation. We therefore suggest that species'' life history will strongly impact the expected cognitive abilities of dispersers, relative to their resident conspecifics, and that cognitive abilities might be an integral part of dispersal syndromes.     

Acquisition of a socially learned tool use sequence in chimpanzees: Implications for cumulative culture

Cumulative culture underpins humanity's enormous success as a species. Claims that other animals are incapable of cultural ratcheting are prevalent, but are founded on just a handful of empirical studies. Whether cumulative culture is unique to humans thus remains a controversial and understudied question that has far-reaching implications for our understanding of the evolution of this phenomenon. We investigated whether one of human's two closest living primate relatives, chimpanzees, are capable of a degree of cultural ratcheting by exposing captive populations to a novel juice extraction task. We found that groups (N = 3) seeded with a model trained to perform a tool modification that built upon simpler, unmodified tool use developed the seeded tool method that allowed greater juice returns than achieved by groups not exposed to a trained model (non-seeded controls; N = 3). One non-seeded group also discovered the behavioral sequence, either by coupling asocial and social learning or by repeated invention. This behavioral sequence was found to be beyond what an additional control sample of chimpanzees (N = 1 group) could discover for themselves without a competent model and lacking experience with simpler, unmodified tool behaviors. Five chimpanzees tested individually with no social information, but with experience of simple unmodified tool use, invented part, but not all, of the behavioral sequence. Our findings indicate that (i) social learning facilitated the propagation of the model-demonstrated tool modification technique, (ii) experience with simple tool behaviors may facilitate individual discovery of more complex tool manipulations, and (iii) a subset of individuals were capable of learning relatively complex behaviors either by learning asocially and socially or by repeated invention over time. That chimpanzees learn increasingly complex behaviors through social and asocial learning suggests that humans' extraordinary ability to do so was built on such prior foundations.     

Review. Studying cumulative cultural evolution in the laboratory

Cumulative cultural evolution is the term given to a particular kind of social learning, which allows for the accumulation of modifications over time, involving a ratchet-like effect where successful modifications are maintained until they can be improved upon. There has been great interest in the topic of cumulative cultural evolution from researchers from a wide variety of disciplines, but until recently there were no experimental studies of this phenomenon. Here, we describe our motivations for developing experimental methods for studying cumulative cultural evolution and review the results we have obtained using these techniques. The results that we describe have provided insights into understanding the outcomes of cultural processes at the population level. Our experiments show that cumulative cultural evolution can result in adaptive complexity in behaviour and can also produce convergence in behaviour. These findings lend support to ideas that some behaviours commonly attributed to natural selection and innate tendencies could in fact be shaped by cultural processes.     

Human cumulative culture: a comparative perspective

Many animals exhibit social learning and behavioural traditions, but human culture exhibits unparalleled complexity and diversity, and is unambiguously cumulative in character. These similarities and differences have spawned a debate over whether animal traditions and human culture are reliant on homologous or analogous psychological processes. Human cumulative culture combines high‐fidelity transmission of cultural knowledge with beneficial modifications to generate a ‘ratcheting’ in technological complexity, leading to the development of traits far more complex than one individual could invent alone. Claims have been made for cumulative culture in several species of animals, including chimpanzees, orangutans and New Caledonian crows, but these remain contentious. Whilst initial work on the topic of cumulative culture was largely theoretical, employing mathematical methods developed by population biologists, in recent years researchers from a wide range of disciplines, including psychology, biology, economics, biological anthropology, linguistics and archaeology, have turned their attention to the experimental investigation of cumulative culture. We review this literature, highlighting advances made in understanding the underlying processes of cumulative culture and emphasising areas of agreement and disagreement amongst investigators in separate fields.     

Cognitive requirements for tool use by New Caledonian crows (Corvus moneduloides)

Abstract

Cumulative technological evolution has been suggested to explain the existence of different pandanus tool designs manufactured by New Caledonian crows. Circumstantial evidence from the distribution of the three tool designs that they manufacture suggests transmission of the designs probably involves accurate social learning, a characteristic considered essential for the cumulative evolution of tools. Recently, Kenward et al. (2005) reported that four hand‐raised crows developed basic stick tool use without social learning. This finding cast doubt on the importance of social learning in the evolution of crows’ pandanus tools in the wild. Here, we report that a naïve male crow at Parc Zoo‐Forestier, Nouméa, developed proficient stick tool use without social input in 2002. In 2004, four captive crows, including the naïve male, that were inexperienced with pandanus material were given an opportunity to use and/or manufacture pandanus tools. Only two of the four birds used the tools but none manufactured tools. Our preliminary findings and the work with the four hand‐raised crows keep open the possibility that the evolution of crows’ pandanus tool designs is based on social learning. We propose that social learning and a disposition to develop basic tool use without social input are both essential cognitive requirements for cumulative technological evolution.     

Prestige-biased cultural learning: bystander's differential attention to potential models influences children's learning

Reasoning about the evolution of our species' capacity for cumulative cultural learning has led culture-gene coevolutionary (CGC) theorists to predict that humans should possess several learning biases which robustly enhance the fitness of cultural learners. Meanwhile, developmental psychologists have begun using experimental procedures to probe the learning biases that young children actually possess — a methodology ripe for testing CGC. Here we report the first direct tests in children of CGC's prediction of prestige bias, a tendency to learn from individuals to whom others have preferentially attended, learned or deferred. Our first study showed that the odds of 3- and 4-year-old children learning from an adult model to whom bystanders had previously preferentially attended for 10 seconds (the prestigious model) were over twice those of their learning from a model whom bystanders ignored. Moreover, this effect appears domain-sensitive: in Study 2 when bystanders preferentially observed a prestigious model using artifacts, she was learned from more often on subsequent artifact-use tasks (odds almost five times greater) but not on food-preference tasks, while the reverse was true of a model who received preferential bystander attention while expressing food preferences.     

Chimpanzee subsistence technology: Materials and skills

Beyond reviewing basic data on Primate technological behavior, the aim of this report is to document the nature of chimpanzee technical skills by examining some of the mental as well as physical expertise which chimpanzees bring to bear on subsistence activities. This task is approached along several avenues: first, an outline is drawn of current knowledge about chimpanzee subsistence technology throughout Africa; second, a sketch is made of technological variability in several chimpanzee populations; third, the results of a personal investigation into the skills needed by chimpanzees to probe for insects are provided; and fourth, a comparison is made of the baboon, chimpanzee and human techniques used to exploit termites as a food resource. Instead of focusing on the unique features of human subsistence technology, the report attempts to show that many technical skills are and probably were firmly rooted in Primate prehistory, well before the advent of the earliest hominids. An integrated model of technological achievements among extant Primates, based on a sample of African cercopithecid, pongid and hominid populations representing stages in a phylogentic sequence, is offered as a foundation for reconstructing the gradual evolution of primate subsistence technology. This approach is intended to provoke contemplation and discussion among those investigators of human behavior and society who favor the thesis that the criterion of technology, together with the cultural transmission of technical skills, separates the human from the nonhuman Primates.     

Why are some numerical concepts more successful than others? An evolutionary perspective on the history of number concepts

From the history of mathematics, it is clear that some numerical concepts are far more pervasive than others. In a densely multimodular mind, evolved cognitive abilities lie at the basis of human culture and cognition. One possible way to explain the differential spread and survival of cultural concepts based on this assumption is the epidemiology of culture. This approach explains the relative success of cultural concepts as a function of their fit with intuitions provided by conceptual modules. A wealth of recent evidence from animal, infant, and neuroimaging studies suggests that human numerical competence is rooted in an evolved number module. In this study, I adopted an epidemiological perspective to examine the cultural transmission of numerical concepts in the history of mathematics. Drawing on historical and anthropological data on number concepts, I will demonstrate that positive integers, zero, and negative numbers have divergent cultural evolutionary histories owing to a distinct relationship with the number module. These case studies provide evidence for the claim that science can be explained in terms of evolved cognitive abilities that are universal in Homo sapiens.     

Social learning and evolution: the cultural intelligence hypothesis

If social learning is more efficient than independent individual exploration, animals should learn vital cultural skills exclusively, and routine skills faster, through social learning, provided they actually use social learning preferentially. Animals with opportunities for social learning indeed do so. Moreover, more frequent opportunities for social learning should boost an individual's repertoire of learned skills. This prediction is confirmed by comparisons among wild great ape populations and by social deprivation and enculturation experiments. These findings shaped the cultural intelligence hypothesis, which complements the traditional benefit hypotheses for the evolution of intelligence by specifying the conditions in which these benefits can be reaped. The evolutionary version of the hypothesis argues that species with frequent opportunities for social learning should more readily respond to selection for a greater number of learned skills. Because improved social learning also improves asocial learning, the hypothesis predicts a positive interspecific correlation between social-learning performance and individual learning ability. Variation among primates supports this prediction. The hypothesis also predicts that more heavily cultural species should be more intelligent. Preliminary tests involving birds and mammals support this prediction too. The cultural intelligence hypothesis can also account for the unusual cognitive abilities of humans, as well as our unique mechanisms of skill transfer.     

Cumulative cultural dynamics and the coevolution of cultural innovation and transmission: an ESS model for panmictic and structured populations

When individuals in a population can acquire traits through learning, each individual may express a certain number of distinct cultural traits. These traits may have been either invented by the individual himself or acquired from others in the population. Here, we develop a game theoretic model for the accumulation of cultural traits through individual and social learning. We explore how the rates of innovation, decay, and transmission of cultural traits affect the evolutionary stable (ES) levels of individual and social learning and the number of cultural traits expressed by an individual when cultural dynamics are at a steady‐state. We explore the evolution of these phenotypes in both panmictic and structured population settings. Our results suggest that in panmictic populations, the ES level of learning and number of traits tend to be independent of the social transmission rate of cultural traits and is mainly affected by the innovation and decay rates. By contrast, in structured populations, where interactions occur between relatives, the ES level of learning and the number of traits per individual can be increased (relative to the panmictic case) and may then markedly depend on the transmission rate of cultural traits. This suggests that kin selection may be one additional solution to Rogers's paradox of nonadaptive culture.     

Endless forms: human behavioural diversity and evolved universals

Human populations have extraordinary capabilities for generating behavioural diversity without corresponding genetic diversity or change. These capabilities and their consequences can be grouped into three categories: strategic (or cognitive), ecological and cultural-evolutionary. Strategic aspects include: (i) a propensity to employ complex conditional strategies, some certainly genetically evolved but others owing to directed invention or to cultural evolution; (ii) situations in which fitness payoffs (or utilities) are frequency-dependent, so that there is no one best strategy; and (iii) the prevalence of multiple equilibria, with history or minor variations in starting conditions (path dependence) playing a crucial role. Ecological aspects refer to the fact that social behaviour and cultural institutions evolve in diverse niches, producing various adaptive radiations and local adaptations. Although environmental change can drive behavioural change, in humans, it is common for behavioural change (especially technological innovation) to drive environmental change (i.e. niche construction). Evolutionary aspects refer to the fact that human capacities for innovation and cultural transmission lead to diversification and cumulative cultural evolution; critical here is institutional design, in which relatively small shifts in incentive structure can produce very different aggregate outcomes. In effect, institutional design can reshape strategic games, bringing us full circle.     

Modeling Coevolution between Language and Memory Capacity during Language Origin

Memory is essential to many cognitive tasks including language. Apart from empirical studies of memory effects on language acquisition and use, there lack sufficient evolutionary explorations on whether a high level of memory capacity is prerequisite for language and whether language origin could influence memory capacity. In line with evolutionary theories that natural selection refined language-related cognitive abilities, we advocated a coevolution scenario between language and memory capacity, which incorporated the genetic transmission of individual memory capacity, cultural transmission of idiolects, and natural and cultural selections on individual reproduction and language teaching. To illustrate the coevolution dynamics, we adopted a multi-agent computational model simulating the emergence of lexical items and simple syntax through iterated communications. Simulations showed that: along with the origin of a communal language, an initially-low memory capacity for acquired linguistic knowledge was boosted; and such coherent increase in linguistic understandability and memory capacities reflected a language-memory coevolution; and such coevolution stopped till memory capacities became sufficient for language communications. Statistical analyses revealed that the coevolution was realized mainly by natural selection based on individual communicative success in cultural transmissions. This work elaborated the biology-culture parallelism of language evolution, demonstrated the driving force of culturally-constituted factors for natural selection of individual cognitive abilities, and suggested that the degree difference in language-related cognitive abilities between humans and nonhuman animals could result from a coevolution with language.     

Innovativeness, population size and cumulative cultural evolution

Henrich [Henrich, J., 2004. Demography and cultural evolution: how adaptive cultural processes can produce maladaptive losses—the Tasmanian case. Am. Antiquity 69, 197-214] proposed a model designed to show that larger population size facilitates cumulative cultural evolution toward higher skill levels. In this model, each newborn attempts to imitate the most highly skilled individual of the parental generation by directly-biased social learning, but the skill level he/she acquires deviates probabilistically from that of the exemplar (cultural parent). The probability that the skill level of the imitator exceeds that of the exemplar can be regarded as the innovation rate. After reformulating Henrich’s model rigorously, we introduce an overlapping-generations analog based on the Moran model and derive an approximate formula for the expected change per generation of the highest skill level in the population. For large population size, our overlapping-generations model predicts a much larger effect of population size than Henrich’s discrete-generations model. We then investigate by way of Monte Carlo simulations the case where each newborn chooses as his/her exemplar the most highly skilled individual from among a limited number of acquaintances. When the number of acquaintances is small relative to the population size, we find that a change in the innovation rate contributes more than a proportional change in population size to the cumulative cultural evolution of skill level.