Evolved Open-Endedness in Cultural Evolution: A New Dimension in Open-Ended Evolution Research.

The goal of Artificial Life research, as articulated by Chris Langton, is "to contribute to theoretical biology by locating life-as-we-know-it within the larger picture of life-as-it-could-be." The study and pursuit of open-ended evolution in artificial evolutionary systems exemplify this goal. However, open-ended evolution research is hampered by two fundamental issues: the struggle to replicate open-endedness in an artificial evolutionary system and our assumption that we only have one system (genetic evolution) from which to draw inspiration. We argue not only that cultural evolution should be seen as another real-world example of an open-ended evolutionary system but that the unique qualities seen in cultural evolution provide us with a new perspective from which we can assess the fundamental properties of, and ask new questions about, open-ended evolutionary systems, especially with regard to evolved open-endedness and transitions from bounded to unbounded evolution. Here we provide an overview of culture as an evolutionary system, highlight the interesting case of human cultural evolution as an open-ended evolutionary system, and contextualize cultural evolution by developing a new framework of (evolved) open-ended evolution. We go on to provide a set of new questions that can be asked once we consider cultural evolution within the framework of open-ended evolution and introduce new insights that we may be able to gain about evolved open-endedness as a result of asking these questions.

Captive great apes tend to innovate simple tool behaviors quickly.

Recent studies have highlighted the important role that individual learning mechanisms and different forms of enhancenment play in the acquisition of novel behaviors by naïve individuals. A considerable subset of these studies has focused on tool innovation by our closest living relatives, the great apes, to better undestand the evolution of technology in our own lineage. To be able to isolate the role that individual learning plays in great ape tool innovation, researchers usually employ what are known as baseline tests. Although these baselines are commonly used in behavioral studies in captivity, the length of these tests in terms of number of trials and duration remains unstandarized across studies. To address this methodological issue, we conducted a literature review of great ape tool innovation studies conducted in zoological institutions and compiled various methodological data including the timing of innovation. Our literature review revealed an early innovation tendency in great apes, which was particularly pronounced when simple forms of tool use were investigated. In the majority of experiments where tool innovation took place, this occurred within the first trial and/or the first hour of testing. We discuss different possible sources of variation in the latency to innovate such as testing setup, species and task. We hope that our literature review helps researchers design more data-informed, resource-efficient experiments on tool innovation in our closest living relatives.

Birch tar production does not prove Neanderthal behavioral complexity.

Birch tar production by Neanderthals-used for hafting tools-has been interpreted as one of the earliest manifestations of modern cultural behavior. This is because birch tar production per se was assumed to require a cognitively demanding setup, in which birch bark is heated in anaerobic conditions, a setup whose inherent complexity was thought to require modern levels of cognition and cultural transmission. Here we demonstrate that recognizable amounts of birch tar were likely a relatively frequent byproduct of burning birch bark (a natural tinder) under common, i.e., aerobic, conditions. We show that when birch bark burns close to a vertical to subvertical hard surface, such as an adjacent stone, birch tar is naturally deposited and can be easily scraped off the surface. The burning of birch bark near suitable surfaces provides useable quantities of birch tar in a single work session (3 h; including birch bark procurement). Chemical analysis of the resulting tar showed typical markers present in archaeological tar. Mechanical tests verify the tar's suitability for hafting and for hafted tools use. Given that similarly sized stones as in our experiment are frequently found in archaeological contexts associated with Neanderthals, the cognitively undemanding connection between burning birch bark and the production of birch tar would have been readily discoverable multiple times. Thus, the presence of birch tar alone cannot indicate the presence of modern cognition and/or cultural behaviors in Neanderthals.

Naïve orangutans (Pongo abelii and Pongo pygmaeus) individually acquire nut-cracking using hammer tools.

Nut-cracking with hammer tools (henceforth: nut-cracking) has been argued to be one of the most complex tool-use behaviors observed in nonhuman animals. So far, only chimpanzees, capuchins, and macaques have been observed using tools to crack nuts in the wild (Boesch and Boesch, 1990; Gumert et al., 2009; Mannu and Ottoni, 2009). However, the learning mechanisms behind this behavior, and the extent of nut-cracking in other primate species are still unknown. The aim of this study was two-fold. First, we investigated whether another great ape species would develop nut-cracking when provided with all the tools and appropriate conditions to do so. Second, we examined the mechanisms behind the emergence of nut-cracking by testing a naïve sample. Orangutans (Pongo abelii and Pongo pygmaeus) have the second most extensive tool-use repertoire among the great apes (after chimpanzees) and show flexible problem-solving capacities. Orangutans have not been observed cracking nuts in the wild, however, perhaps because their arboreal habits provide limited opportunities for nut-cracking. Therefore, orangutans are a valid candidate species for the investigation of the development of this behavior. Four nut-cracking-naïve orangutans at Leipzig zoo (P. abelii; Mage = 16; age range = 10-19; 4F; at the time of testing) were provided with nuts and hammers but were not demonstrated the nut-cracking behavioral form. Additionally, we report data from a previously unpublished study by one of the authors (Martina Funk) with eight orangutans housed at Zürich zoo (six P. abelii and two P. pygmaeus; Mage = 14; age range = 2-30; 5F; at the time of testing) that followed a similar testing paradigm. Out of the twelve orangutans tested, at least four individuals, one from Leipzig (P. abelii) and three from Zürich (P. abelii and P. pygmaeus), spontaneously expressed nut-cracking using wooden hammers. These results demonstrate that nut-cracking can emerge in orangutans through individual learning and certain types of non-copying social learning.

Examining the mechanisms underlying the acquisition of animal tool behaviour.

Despite major advances in the study of animal tool behaviour, researchers continue to debate how exactly certain behaviours are acquired. While specific mechanisms, such as genetic predispositions or action copying, are sometimes suspected to play a major role in behavioural acquisition, controlled experiments are required to provide conclusive evidence. In this opinion piece, we refer to classic ethological methodologies to emphasize the need for studying the relative contributions of different factors to the emergence of specific tool behaviours. We describe a methodology, consisting of a carefully staged series of baseline and social-learning conditions, that enables us to tease apart the roles of different mechanisms in the development of behavioural repertoires. Experiments employing our proposed methodology will not only advance our understanding of animal learning and culture, but as a result, will also help inform hypotheses about human cognitive, cultural and technological evolution. More generally, our conceptual framework is suitable for guiding the detailed investigation of other seemingly complex animal behaviours.

Individual acquisition of "stick pounding" behavior by naïve chimpanzees.

Many studies investigating culture in nonhuman animals tend to focus on the inferred need of social learning mechanisms that transmit the form of a behavior to explain the population differences observed in wild animal behavioral repertoires. This research focus often results in studies overlooking the possibility of individuals being able to develop behavioral forms without requiring social learning. The disregard of individual learning abilities is most clearly observed in the nonhuman great ape literature, where there is a persistent claim that chimpanzee behaviors, in particular, require various forms of social learning mechanisms. These special social learning abilities have been argued to explain the acquisition of the relatively large behavioral repertoires observed across chimpanzee populations. However, current evidence suggests that although low-fidelity social learning plays a role in harmonizing and stabilizing the frequency of behaviors within chimpanzee populations, some (if not all) of the forms that chimpanzee behaviors take may develop independently of social learning. If so, they would be latent solutions-behavioral forms that can (re-)emerge even in the absence of observational opportunities, via individual (re)innovations. Through a combination of individual and low-fidelity social learning, the population-wide patterns of behaviors observed in great ape species are then established and stably maintained. This is the Zone of Latent Solutions (ZLS) hypothesis. The current study experimentally tested the ZLS hypothesis for pestle pounding, a wild chimpanzee behavior. We tested the reinnovation of this behavior in semi-wild chimpanzees at Chimfunshi Wildlife Orphanage in Zambia, Africa, (N = 90, tested in four social groups). Crucially, all subjects were naïve to stick pounding before testing. Three out of the four tested groups reinnovated stick pounding-clearly demonstrating that this behavioral form does not require social learning. These findings provide support for the ZLS hypothesis alongside further evidence for the individual learning abilities of chimpanzees.

Differences in novel food response between Pongo and Pan.

The diversity of great ape diets requires behavioral flexibility. Consequently, the exploration of potentially novel food sources is supposedly beneficial, but simultaneously, apes show high neophobia to prevent harmful and poisonous food intake. Social information, such as presence of group members or observations of non-naïve, experienced individuals have been demonstrated to affect the acceptance of novel food items in primates. Sociality may have evolutionary effects on the response of apes to novel foods. Here we assess the social information hypothesis, which predicts that selection favors higher neophobia in species where social information is abundant. We report the results from 134 great apes housed in multiple facilities from four closely related species that naturally differ in their degree of sociality: Pongo pygmaeus, Pongo abelii, Pan troglodytes and Pan paniscus. We examined individuals' reactions to novel foods when alone, which enabled us to detect any inherent differences and revealed significant distinctions between species. Chimpanzees and bonobos, that are naturally exposed to higher amounts of social information, were less likely to consume novel foods alone (showed higher neophobia) than the two more solitary orangutan species. Chimpanzees were especially cautious and showed higher explorative behaviors before tasting novel food than other species. Age influenced neophobia as younger individuals of all species took longer to taste novel foods than adults did.

Could nonhuman great apes also have cultural evolutionary psychology?

Attempted answers are given to (a) whether nonhuman great apes (apes) also have evolved imitation (answer: no); (b) whether humans can transmit imitation as a gadget to apes (answer: yes, partly); (c) whether human-to-ape transmission can kickstart subsequent and stable ape cultural evolutionary psychology ("CEP"; answer: unlikely); and (d) when CEP evolved in our lineage (answer: relatively late).

Is Overimitation a Uniquely Human Phenomenon? Insights From Human Children as Compared to Bonobos.

Imitation is a key mechanism of human culture and underlies many of the intricacies of human social life, including rituals and social norms. Compared to other animals, humans appear to be special in their readiness to copy novel actions as well as those that are visibly causally irrelevant. This study directly compared the imitative behavior of human children to that of bonobos, our understudied great ape relatives. During an action-copying task involving visibly causally irrelevant actions, only 3- to 5-year-old children (N = 77) readily copied, whereas no bonobo from a large sample did (N = 46). These results highlight the distinctive nature of the human cultural capacity and contribute important insights into the development and evolution of human cultural behaviors.

What drives young children to over-imitate? Investigating the effects of age, context, action type, and transitivity.

Imitation underlies many traits thought to characterize our species, which includes the transmission and acquisition of language, material culture, norms, rituals, and conventions. From early childhood, humans show an intriguing willingness to imitate behaviors, even those that have no obvious function. This phenomenon, known as "over-imitation," is thought to explain some of the key differences between human cultures as compared with those of nonhuman animals. Here, we used a single integrative paradigm to simultaneously investigate several key factors proposed to shape children's over-imitation: age, context, transitivity, and action type. We compared typically developing children aged 4-6years in a task involving actions verbally framed as being instrumental, normative, or communicative in function. Within these contexts, we explored whether children were more likely to over-imitate transitive versus intransitive actions and manual versus body part actions. Results showed an interaction between age and context; as children got older, they were more likely to imitate within a normative context, whereas younger children were more likely to imitate in instrumental contexts. Younger children were more likely to imitate transitive actions (actions on objects) than intransitive actions compared with older children. Our results show that children are highly sensitive to even minimal cues to perceived context and flexibly adapt their imitation accordingly. As they get older, children's imitation appears to become less object bound, less focused on instrumental outcomes, and more sensitive to normative cues. This shift is consistent with the proposal that over-imitation becomes increasingly social in its function as children move through childhood and beyond.

Chimpanzees create and modify probe tools functionally: A study with zoo-housed chimpanzees.

Chimpanzees (Pan troglodytes) use tools to probe for out-of-reach food, both in the wild and in captivity. Beyond gathering appropriately-sized materials to create tools, chimpanzees also perform secondary modifications in order to create an optimized tool. In this study, we recorded the behavior of a group of zoo-housed chimpanzees when presented with opportunities to use tools to probe for liquid foods in an artificial termite mound within their enclosure. Previous research with this group of chimpanzees has shown that they are proficient at gathering materials from within their environment in order to create tools to probe for the liquid food within the artificial mound. Extending beyond this basic question, we first asked whether they only made and modified probe tools when it was appropriate to do so (i.e. when the mound was baited with food). Second, by collecting continuous data on their behavior, we also asked whether the chimpanzees first (intentionally) modified their tools prior to probing for food or whether such modifications occurred after tool use, possibly as a by-product of chewing and eating the food from the tools. Following our predictions, we found that tool modification predicted tool use; the chimpanzees began using their tools within a short delay of creating and modifying them, and the chimpanzees performed more tool modifying behaviors when food was available than when they could not gain food through the use of probe tools. We also discuss our results in terms of the chimpanzees' acquisition of the skills, and their flexibility of tool use and learning.

Cognitive mechanisms matter - but they do not explain the absence of teaching in chimpanzees.

Kline's functional categories for the evolution of teaching blur some valuable distinctions. Moreover, her account provides no answer to the question of why direct active teaching seems to be a uniquely human phenomenon.

Why do chimpanzees hunt? Considering the benefits and costs of acquiring and consuming vertebrate versus invertebrate prey.

Understanding the benefits and costs of acquiring and consuming different forms of animal matter by primates is critical for identifying the selective pressures responsible for increased meat consumption in the hominin lineage. Chimpanzees (Pan troglodytes) are unusual among primates in the amount of vertebrate prey they consume. Still, surprisingly little is known about the nutritional benefits of eating meat for this species. In order to understand why chimpanzees eat vertebrates, it is critical to consider the relative benefits and costs of other types of faunivory - including invertebrates. Although we lack specific nutritional data on the flesh and organs of chimpanzee prey, the macronutrient profiles of insects and wild vertebrate meat are generally comparable on a gram-to-gram basis. There are currently very few data on the micronutrient (vitamin and mineral) content of meat consumed by chimpanzees. With few exceptions, the advantages of hunting vertebrate prey include year-round availability, rapid acquisition of larger packages and reduced handling/processing time (once prey are encountered or detected). The disadvantages of hunting vertebrate prey include high potential acquisition costs per unit time (energy expenditure and risk of injury) and greater contest competition with conspecifics. Acquiring an equivalent mass of invertebrates (to match even a small scrap of meat) is possible, but typically takes more time. Furthermore, in contrast to vertebrate prey, some insect resources are effectively available only at certain times of the year. Here we identify the critical data needed to test our hypothesis that meat scraps may have a higher (or at least comparable) net benefit:cost ratio than insect prey. This would support the 'meat scrap' hypothesis as an explanation for why chimpanzees hunt in groups even when doing so does not maximize an individual's energetic gain.

Limitations to the cultural ratchet effect in young children.

Although many animal species show at least some evidence of cultural transmission, broadly defined, only humans show clear evidence of cumulative culture. In the current study, we investigated whether young children show the "ratchet effect," an important component of cumulative culture--the ability to accumulate efficient modifications across generations. We tested 16 diffusion chains--altogether consisting of 80 children--to see how they solved an instrumental task (i.e., carrying something from one location to another). We found that when the chain was seeded with an inefficient way of solving the task, 4-year-olds were able to innovate and transmit these innovations so as to reach a more efficient solution. However, when it started out with relatively efficient solutions already (i.e., the ones that children in a control condition discovered for themselves), there were no further techniques invented and/or transmitted beyond that. Thus, young children showed the ratchet effect to a limited extent, accumulating efficient modifications but not going beyond the inventive level of the individual.

Naïve, adult, captive chimpanzees do not socially learn how to make and use sharp stone tools.

Although once regarded as a unique human feature, tool-use is widespread in the animal kingdom. Some of the most proficient tool-users are our closest living relatives, chimpanzees. These repertoires however consist primarily of tool use, rather than tool manufacture (for later use). Furthermore, most populations of chimpanzees use organic materials, such as sticks and leaves, rather than stones as tools. This distinction may be partly ecological, but it is also important as chimpanzees are often used as models for the evolution of human material culture, the oldest traces of which consist of manufactured sharp stone tools (so-called "flakes"). Thus, examining the conditions (if any) under which chimpanzees may develop flake manufacture and use can provide insight into the drivers of these behaviours in our own lineage. Previous studies on non-human apes' ability to make and use flakes focused on enculturated apes, giving them full demonstrations of the behaviour immediately, without providing social information on the task in a stepwise manner. Here we tested naïve, captive chimpanzees (N = 4; three potentially enculturated and one unenculturated subject) in a social learning experimental paradigm to investigate whether enculturated and/or unenculturated chimpanzees would develop flake making and use after social information of various degrees (including a human demonstration) was provided in a scaffolded manner. Even though social learning opportunities were provided, neither the unenculturated subject nor any of the potentially enculturated subjects made or used flakes, in stark contrast to previous studies with enculturated apes. These data suggest that flake manufacture and use is outside of our tested group of captive chimpanzees' individual and social learning repertoires. It also suggests that high levels of enculturation alongside human demonstrations (and/or training) may be required before captive chimpanzees can develop this behaviour.

Bone-related behaviours of captive chimpanzees (Pan troglodytes) during two excavating experiments.

After stone tools, bone tools are the most abundant artefact type in the Early Pleistocene archaeological record. That said, they are still relatively scarce, which limits our understanding of the behaviours that led to their production and use. Observations of extant primates constitute a unique source of behavioural data with which to construct hypotheses about the technological forms and repertoires exhibited by our hominin ancestors. We conducted two different experiments to investigate the behavioural responses of two groups of captive chimpanzees (Pan troglodytes; n = 33 and n = 9) to disarticulated, defleshed, ungulate bones while participating in a foraging task aimed at eliciting excavating behaviour. Each chimpanzee group was provided with bone specimens with different characteristics, and the two groups differed in their respective experience levels with excavating plant tools. We found that several individuals from the inexperienced group used the provided bones as tools during the task. In contrast, none of the individuals from the experienced group used bones as excavating tools, but instead continued using plant tools. These chimpanzees also performed non-excavating bone behaviours such as percussion and tool-assisted extraction of organic material from the medullary cavity. Our findings serve as a proof-of-concept that chimpanzees can be used to investigate spontaneous bone tool behaviours such as bone-assisted excavation. Furthermore, our results raise interesting questions regarding the role that bone characteristics, as well as previous tool-assisted excavating experience with other raw materials, might have in the expression of bone tool-assisted excavation.

Social organization and the evolution of cumulative technology in apes and hominins.

Culturally supported accumulation (or ratcheting) of technological complexity is widely seen as characterizing hominin technology relative to that of the extant great apes, and thus as representing a threshold in cultural evolution. To explain this divide, we modeled the process of cultural accumulation of technology, which we defined as adding new actions to existing ones to create new functional combinations, based on a model for great ape tool use. The model shows that intraspecific and interspecific variation in the presence of simple and cumulative technology among extant orangutans and chimpanzees is largely due to variation in sociability, and hence opportunities for social learning. The model also suggests that the adoption of extensive allomaternal care (cooperative breeding) in early Pleistocene Homo, which led to an increase in sociability and to teaching, and hence increased efficiency of social learning, was enough to facilitate technological ratcheting. Hence, socioecological changes, rather than advances in cognitive abilities, can account for the cumulative cultural changes seen until the origin of the Acheulean. The consequent increase in the reliance on technology could have served as the pacemaker for increased cognitive abilities. Our results also suggest that a more important watershed in cultural evolution was the rise of donated culture (technology or concepts), in which technology or concepts was transferred to naïve individuals, allowing them to skip many learning steps, and specialization arose, which allowed individuals to learn only a subset of the population's skills.

Punishing for your own good: the case of reputation-based cooperation.

Contrary to Guala, I claim that several mechanisms can explain punishment in humans. Here I focus on reputation-based cooperation--and I explore how it can lead to punishment under situations that may or may not be perceived as being anonymous. Additionally, no particular mechanism stands out in predicting an excess of punishment under constrained lab conditions.