Capuchin monkeys learn to use information equally well from individual exploration and social demonstration

The limited evidence of complex culture in non-human primates contrasts strikingly with human behaviour. This may be because non-human primates fail to use information acquired socially as effectively as they use information acquired individually. Here, monkeys were trained on a stimulus discrimination task with a win-stay, lose-shift (WSLS) reward structure. In a social learning condition, the experimenter performed an information trial by choosing between the available stimuli; in an individual condition, monkeys made this choice themselves. The monkeys' subsequent test trials displayed the same stimulus array. They were rewarded for repetition of rewarded ('win-stay') and avoidance of unrewarded ('lose-shift') information trial selections. Nine monkeys reached our pre-determined performance criterion on the initial two-stimulus stage. Their ability to generalise the WSLS strategy was then evaluated by transfer to a three-stimulus stage. Minimal differences were found in information use between the social and individual conditions on two-stimuli. However, a bias was found towards repetition of the information trial, regardless of information source condition or whether the information trial selection was rewarded. Proficient subjects were found to generalise the strategy to three-stimuli following rewarded information trials, but performed at chance on unrewarded. Again, this was not found to vary by source condition. Overall, results suggest no fundamental barrier to non-human primates' use of information from a social source. However, the apparent struggle to learn from the absence of rewards hints at a difficulty with using information acquired from unsuccessful attempts; this could be linked to the limited evidence for cumulative culture in non-human primates.

Taking account of others' goals in social information use: Developmental changes in 3- to 7-year-old children

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Social information use improved with age but only for exploration of alternatives.

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Children were able to account for others’ conflicting motivations from 4 years.

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Alignment of the demonstrator’s and children’s goals did not influence performance.

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From 6 years children could infer the outcome of others’ behaviour.

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Rates of copying were low at all ages, even when it was the appropriate response.

The ability to take mental states such as goals into account when interpreting others’ behavior has been proposed to be what sets human use of social information apart from that of other animals. If so, children’s social information use would be expected to change as their understanding of others’ mental states develops. We explored age-related changes in 3- to 7-year-old children’s ability to strategically use social information by taking into account another’s goal when it was, or was not, aligned with their own. Children observed as a puppet demonstrator selected a capsule, peeked inside, and chose to accept or reject it, following which children made their own selection. Children were able to account for others’ conflicting motivations from around 4 years of age and reliably inferred the outcome of others’ behavior from 6 years. However, using social information based on such inferences appeared to be challenging regardless of whether the demonstrator’s goal was, or was not. aligned to that of the participant. We found that social information use improved with age; however, this improvement was restricted to cases in which the appropriate response was to avoid copying the demonstrator’s selection. In contrast to previous research, appropriate copying responses remained at chance. Possible explanations for this unexpected pattern of results are discussed. The cognitive challenge associated with the ability to account for others’ goals could offer humans a significant advantage over that of other animals in their ability to use social information.

Beyond social learning

Cultural evolution requires the social transmission of information. For this reason, scholars have emphasized social learning when explaining how and why culture evolves. Yet cultural evolution results from many mechanisms operating in concert. Here, we argue that the emphasis on social learning has distracted scholars from appreciating both the full range of mechanisms contributing to cultural evolution and how interactions among those mechanisms and other factors affect the output of cultural evolution. We examine understudied mechanisms and other factors and call for a more inclusive programme of investigation that probes multiple levels of the organization, spanning the neural, cognitive-behavioural and populational levels. To guide our discussion, we focus on factors involved in three core topics of cultural evolution: the emergence of culture, the emergence of cumulative cultural evolution and the design of cultural traits. Studying mechanisms across levels can add explanatory power while revealing gaps and misconceptions in our knowledge. This article is part of the theme issue 'Foundations of cultural evolution'.

Limited evidence for executive function load impairing selective copying in a win-stay lose-shift task

The use of ‘explicitly metacognitive’ learning strategies has been proposed as an explanation for uniquely human capacities for cumulative culture. Such strategies are proposed to rely on explicit, system-2 cognitive processes, to enable advantageous selective copying. To investigate the plausibility of this theory, we investigated participants’ ability to make flexible learning decisions, and their metacognitive monitoring efficiency, under executive function (EF) load. Adult participants completed a simple win-stay lose-shift (WSLS) paradigm task, intended to model a situation where presented information can be used to inform response choice, by copying rewarded responses and avoiding those that are unrewarded. This was completed alongside a concurrent switching task. Participants were split into three conditions: those that needed to use a selective copying, WSLS strategy, those that should always copy observed information, and those that should always do the opposite (Expt 1). Participants also completed a metacognitive monitoring task alongside the concurrent switching task (Expt 2). Conditions demanding selective strategies were more challenging than those requiring the use of one rule consistently. In addition, consistently copying was less challenging than consistently avoiding observed stimuli. Differences between selectively copying and always copying were hypothesised to stem from working memory requirements rather than the concurrent EF load. No impact of EF load was found on participants’ metacognitive monitoring ability. These results suggest that copying decisions are underpinned by the use of executive functions even at a very basic level, and that selective copying strategies are more challenging than a combination of their component parts. We found minimal evidence that selective copying strategies relied on executive functions any more than consistent copying or deviation. However, task experience effects suggested that ceiling effects could have been masking differences between conditions which might be apparent in other contexts, such as when observed information must be retained in memory.

Cognitive prerequisites for cumulative culture are context-dependent: Children's potential for ratcheting depends on cue longevity

Human cumulative culture has been suggested to depend on human-unique cognitive mechanisms, explaining its apparent absence in other species. We show that the potential for exhibiting cumulative culture depends on the cognitive abilities of the agents and the demands associated with using information generated by others' activity. 154 children aged 3-6 years played a searching game ("Find the Treasure"), taking their turn after a puppet demonstrator. The puppet's attempt revealed information about the contents of the locations searched, which could be exploited to target rewarded locations, and avoid unrewarded ones. Two conditions were presented, intended to capture realistic variation in the transience of the cues generated by another individual's activity. In one condition, the puppet's demonstration provided transient information - boxes were opened, seen to be rewarded or not, and then closed. In the other condition the puppet's chosen boxes remained partially open, providing an enduring visible cue as to whether that location was rewarded. Children undertook three trials of varying demonstration success, and we used patterns of performance to infer the potential for improvement over multiple generations of transmission. In the Enduring Cues condition, children's performance demonstrated the potential for cumulative culture. In contrast, in the Transient Information condition, only older children showed improved performances following higher success demonstrations and overall performance was not compatible with the possibility of improvements over generations of social transmission. We conclude that under certain conditions cumulative culture could occur in many species, but in a broader range of contexts in humans.

The value of teaching increases with tool complexity in cumulative cultural evolution

Human cumulative cultural evolution (CCE) is recognized as a powerful ecological and evolutionary force, but its origins are poorly understood. The long-standing view that CCE requires specialized social learning processes such as teaching has recently come under question, and cannot explain why such processes evolved in the first place. An alternative, but largely untested, hypothesis is that these processes gradually coevolved with an increasing reliance on complex tools. To address this, we used large-scale transmission chain experiments (624 participants), to examine the role of different learning processes in generating cumulative improvements in two tool types of differing complexity. Both tool types increased in efficacy across experimental generations, but teaching only provided an advantage for the more complex tools. Moreover, while the simple tools tended to converge on a common design, the more complex tools maintained a diversity of designs. These findings indicate that the emergence of cumulative culture is not strictly dependent on, but may generate selection for, teaching. As reliance on increasingly complex tools grew, so too would selection for teaching, facilitating the increasingly open-ended evolution of cultural artefacts.

The value of teaching increases with tool complexity in cumulative cultural evolution

Human cumulative cultural evolution (CCE) is recognized as a powerful ecological and evolutionary force, but its origins are poorly understood. The long-standing view that CCE requires specialized social learning processes such as teaching has recently come under question, and cannot explain why such processes evolved in the first place. An alternative, but largely untested, hypothesis is that these processes gradually coevolved with an increasing reliance on complex tools. To address this, we used large-scale transmission chain experiments (624 participants), to examine the role of different learning processes in generating cumulative improvements in two tool types of differing complexity. Both tool types increased in efficacy across experimental generations, but teaching only provided an advantage for the more complex tools. Moreover, while the simple tools tended to converge on a common design, the more complex tools maintained a diversity of designs. These findings indicate that the emergence of cumulative culture is not strictly dependent on, but may generate selection for, teaching. As reliance on increasingly complex tools grew, so too would selection for teaching, facilitating the increasingly open-ended evolution of cultural artefacts.

Robust, source-independent biases in children's use of socially and individually acquired information

Culture has an extraordinary influence on human behavior, unparalleled in other species. Some theories propose that humans possess learning mechanisms biologically selected specifically for social learning, which function to promote rapid enculturation. If true, it follows that information acquired via observation of another's activity might be responded to differently, compared with equivalent information acquired through one's own exploration, and that this should be the case in even very young children. To investigate this, we compared children's responses to information acquired either socially or from personal experience. The task we used allowed direct comparison between these alternative information sources, as the information value was equivalent across conditions, which has not been true of previous methods used to tackle similar questions. Across two 18-month- to 5-year-old samples (recruited in the United Kingdom and China), we found that children performed similarly following information acquired from social demonstrations, compared with personal experience. Children's use of the information thus appeared independent of source. Furthermore, children's suboptimal performance showed evidence of a consistent bias driven by motivation for exploration as well as exploitation, which was apparent across both conditions and in both samples. Our results are consistent with the view that apparent peculiarities identified in human social information use could be developmental outcomes of general-purpose learning and motivational biases, as opposed to mechanisms that have been biologically selected specifically for the acquisition of cultural information. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Inferring Behavior From Partial Social Information Plays Little or No Role in the Cultural Transmission of Adaptive Traits

Many human cultural traits become increasingly beneficial as they are repeatedly transmitted, thanks to an accumulation of modifications made by successive generations. But how do later generations typically avoid modifications which revert traits to less beneficial forms already sampled and rejected by earlier generations? And how can later generations do so without direct exposure to their predecessors' behavior? One possibility is that learners are sensitive to cues of non-random production in others' behavior, and that particular variants (e.g., those containing structural regularities unlikely to occur spontaneously) have been produced deliberately and with some effort. If this non-random behavior is attributed to an informed strategy, then the learner may infer that apparent avoidance of certain possibilities indicates that these have already been sampled and rejected. This could potentially prevent performance plateaus resulting from learners modifying inherited behaviors randomly. We test this hypothesis in four experiments in which participants, either individually or in interacting dyads, attempt to locate rewards in a search grid, guided by partial information about another individual's experience of the task. We find that in some contexts, valid inferences about another's behavior can be made from partial information, and these inferences can be used in a way which facilitates trait adaptation. However, the benefit of these inferences appears to be limited, and in many contexts-including some which have the potential to make inferring the experience of another individual easier-there appears to be no benefit at all. We suggest that inferring previous behavior from partial social information plays a minimal role in the adaptation of cultural traits.

Celebrating the continued importance of "Machiavellian Intelligence" 30 years on

The question of what has shaped primates' (and other species') cognitive capacities, whether technical or social demands, remains a hot topic of inquiry. Indeed, a key area of study within the field of comparative psychology in the last few decades has been the focus on social life as a driving force behind the evolution of cognition, studied from behavioral and neurological perspectives and from theoretical and empirical perspectives. Reflecting on contemporary studies of primate social cognition specifically, one cannot ignore the book, Machiavellian Intelligence, coedited by Richard Byrne and Andrew Whiten (Byrne & Whiten, 1988a). It is a keystone for the field: The volume as a whole has been cited over 3,000 times, without even including citations to individual chapters. This year, 2018, is the 30th anniversary of the first publication of Machiavellian Intelligence, and with this special issue of the Journal of Comparative Psychology, we mark that milestone. The key concept put forth in Machiavellian Intelligence was that primates' sociocognitive abilities were shaped by the complex social worlds that they inhabited, rather than the technical or foraging challenges that they faced, as had previously been posited. In this issue, we consider the strength of the Machiavellian intelligence hypothesis 30 years on to explain primate social cognition, and we consider its applicability to nonprimate species and to other cognitive domains. (PsycINFO Database Record (c) 2018 APA, all rights reserved).

Squirrel monkey responses to information from social demonstration and individual exploration using touchscreen and object choice tasks

We aimed to study whether a non-human primate species responded differently to information acquired socially compared with that acquired individually. To do so, we attempted to train squirrel monkeys to perform binary discriminations. These involved exposure to either social information (human or puppet demonstrator performs an initial 'information trial') or individual exploration (monkey performs information trial as well as subsequent test trials). In Experiment 1, we presented the task on a touchscreen tablet. Only one monkey appeared to learn the significance of the information trial, and across the group there was no improvement in performance over sessions. The proficient individual showed little evidence of successful transfer to three-way discrimination problems, suggesting limited representation of the task structure. In Experiment 2, we used a logically identical task, presented as a physical object choice (inverted cups concealing a food reward). No monkeys learned to use the information trial cues, and success again did not increase over sessions. We concluded that the monkeys' poor performance in Experiment 1 was not attributable to the mode of presentation (touchscreen), but reflected real difficulties with mastering the task structure. For both experiments, we analysed the monkeys' spontaneous responses to the different trial types (social-win, social-lose, individual-win, and individual-lose). We found that monkeys had a tendency to repeat selections made during the information trial, whether these were made by themselves or by a demonstrator. This tendency to repeat was observed even following lose trials (i.e. when incorrect). Apparent 'success' following win trials was probably largely an artefact of behavioural inertia (individual learning conditions) and stimulus enhancement (social learning conditions), rather than sensitivity to the reward cues associated with that stimulus. Although monkeys did respond somewhat differently (more repeats) following win trials, compared with lose trials, this was no more apparent in the object choice task than the touchscreen task, again suggesting that the less ecologically valid presentation medium did not actively disrupt potential for learning the discrimination rule. Both touchscreen and physical object choice tasks appear to be valid methods to study learning in squirrel monkeys, with neither method giving a clear performance advantage over the other. However, this population did not master the contingencies in these tasks.

Experimental assessment of capacities for cumulative culture: Review and evaluation of methods

In the current literature, there are few experimental tests of capacities for cumulative cultural evolution in nonhuman species. There are even fewer examples of such tests in young children. This limited evidence is noteworthy given widespread interest in the apparent distinctiveness of human cumulative culture, and the potentially significant theoretical implications of identifying related capacities in nonhumans or very young children. We evaluate experimental methods upon which claims of capacities for cumulative culture, or lack thereof, have been based. Although some of the established methods (those simulating generational succession) have the potential to identify positive evidence that fulfills widely accepted definitions of cumulative culture, the implementation of these methods entails significant logistical challenges. This is particularly true for testing populations that are difficult to access in large numbers, or those not amenable to experimental control. This presents problems for generating evidence that would be sufficient to support claims of capacities for cumulative culture, and these problems are magnified for establishing convincing negative evidence. We discuss alternative approaches to assessing capacities for cumulative culture, which circumvent logistical problems associated with experimental designs involving chains of learners. By inferring the outcome of repeated transmission from the input–output response patterns of individual subjects, sample size requirements can be massively reduced. Such methods could facilitate comparisons between populations, for example, different species, or children of a range of ages. We also detail limitations and challenges of this alternative approach, and discuss potential avenues for future research.

This article is categorized under:

Cognitive Biology > Evolutionary Roots of Cognition

Cognitive Biology > Cognitive Development

Psychology > Comparative Psychology

Using Experimental Research Designs to Explore the Scope of Cumulative Culture in Humans and Other Animals

In humans, cultural evolutionary processes are capable of shaping our cognition, because the conceptual tools we learn from others enable mental feats which otherwise would be beyond our capabilities. This is possible because human culture supports the intergenerational accumulation of skills and knowledge, such that later generations can benefit from the experience and exploration efforts of their predecessors. However, it remains unclear how exactly human social transmission supports the accumulation of advantageous traits, and why we see little evidence of this in the natural behavior of other species. Thus, it is difficult to know whether the cognitive abilities of other animals might be similarly scaffolded by processes of cultural evolution. In this article, I discuss how experimental studies of cultural evolution have contributed to our understanding of human cumulative culture, as well as some of the limitations of these approaches. I also discuss how similar research designs can be used to evaluate the potential for cumulative culture in other species. Such research may be able to clarify what distinguishes human cumulative culture from related phenomena in nonhumans, shedding light on the issue of whether other species also have the potential to develop cognitive capacities that are outcomes of cultural evolution.

Culture drives cognitive evolution by supporting the transmission and intergenerational accumulation of skills and knowledge, based on social learning and teaching: Later generations benefit from what their predecessors acquired. Taking a metaperspective on those experimental studies that explore the mechanisms underlying cultural transmission, Caldwell discusses their potential for generating valuable insights, their possible limitations, and their generalizability to other species.

Action-matching biases in monkeys (Sapajus spp.) in a stimulus-response compatibility task: Evaluating experience-dependent malleability

Stimulus-response (S-R) compatibility effects occur when observing certain stimuli facilitate the performance of a related response and interfere with performing an incompatible or different response. Using stimulus-response action pairings, this phenomenon has been used to study imitation effects in humans, and here we use a similar procedure to examine imitative biases in nonhuman primates. Eight capuchin monkeys (Sapajus spp.) were trained to perform hand and mouth actions in a stimulus-response compatibility task. Monkeys rewarded for performing a compatible action (i.e., using their hand or mouth to perform an action after observing an experimenter use the same effector) performed significantly better than those rewarded for incompatible actions (i.e., performing an action after observing an experimenter use the other effector), suggesting an initial bias for imitative action over an incompatible S-R pairing. After a predetermined number of trials, reward contingencies were reversed; that is, monkeys initially rewarded for compatible responses were now rewarded for incompatible responses, and vice versa. In this 2nd training stage, no difference in performance was identified between monkeys rewarded for compatible or incompatible actions, suggesting any imitative biases were now absent. In a 2nd experiment, 2 monkeys learned both compatible and incompatible reward contingencies in a series of learning reversals. Overall, no difference in performance ability could be attributed to the type of rule (compatible-incompatible) being rewarded. Together, these results suggest that monkeys exhibit a weak bias toward action copying, which (in line with findings from humans) can largely be eliminated through counterimitative experience. (PsycINFO Database Record

Human Teaching and Cumulative Cultural Evolution

Although evidence of teaching behaviour has been identified in some nonhuman species, human teaching appears to be unique in terms of both the breadth of contexts within which it is observed, and in its responsiveness to needs of the learner. Similarly, cultural evolution is observable in other species, but human cultural evolution appears strikingly distinct. This has led to speculation that the evolutionary origins of these capacities may be causally linked. Here we provide an overview of contrasting perspectives on the relationship between teaching and cultural evolution in humans, and briefly review previous research which suggests that cumulative culture (here meaning cultural evolution featuring a trend towards improving functionality) can occur without teaching. We then report the results of a novel experimental study in which we investigated how the benefits of teaching may depend on the complexity of the skill to be acquired. Participants were asked to tie knots of varying complexity. In our Teaching condition, opportunities to interact with an experienced partner aided transmission of the most complex knots, but not simpler equivalents, relative to exposure to completed products alone (End State Only condition), and also relative to information about the process of completion (Intermediate States condition). We conclude by considering the plausibility of various accounts of the evolutionary relationship between teaching and cultural evolution in humans.

Experimental approaches to studying cumulative cultural evolution

In humans, cultural traditions often change in ways which increase efficiency and functionality. This process, widely referred to as cumulative cultural evolution, sees beneficial traits preferentially retained, and it is so pervasive that we may be inclined to take it for granted. However, directional change of this kind appears to distinguish human cultural traditions from behavioural traditions that have been documented in other animals. Cumulative culture is therefore attracting an increasing amount of attention within psychology, and researchers have begun to develop methods of studying this phenomenon under controlled conditions. These studies have now addressed a number of different questions, including which learning mechanisms may be implicated, and how the resulting behaviours may be influenced by factors such as population structure. The current article provides a synopsis of some of these studies, and highlights some of the unresolved issues in this field.

Identifying innovation in laboratory studies of cultural evolution: rates of retention and measures of adaptation

In recent years, laboratory studies of cultural evolution have become increasingly prevalent as a means of identifying and understanding the effects of cultural transmission on the form and functionality of transmitted material. The datasets generated by these studies may provide insights into the conditions encouraging, or inhibiting, high rates of innovation, as well as the effect that this has on measures of adaptive cultural change. Here we review recent experimental studies of cultural evolution with a view to elucidating the role of innovation in generating observed trends. We first consider how tasks are presented to participants, and how the corresponding conceptualization of task success is likely to influence the degree of intent underlying any deviations from perfect reproduction. We then consider the measures of interest used by the researchers to track the changes that occur as a result of transmission, and how these are likely to be affected by differing rates of retention. We conclude that considering studies of cultural evolution from the perspective of innovation provides us with valuable insights that help to clarify important differences in research designs, which have implications for the likely effects of variation in retention rates on measures of cultural adaptation.

Cultural diffusion in humans and other animals

Recent years have seen an enormous expansion and progress in studies of the cultural diffusion processes through which behaviour patterns, ideas and artifacts are transmitted within and between generations of humans and other animals. The first of two main approaches focuses on identifying, tracing and understanding cultural diffusion as it naturally occurs, an essential foundation to any science of culture. This endeavor has been enriched in recent years by sophisticated statistical methods and surprising new discoveries particularly in humans, other primates and cetaceans. This work has been complemented by a growing corpus of powerful, purpose-designed cultural diffusion experiments with captive and natural populations that have facilitated the rigorous identification and analysis of cultural diffusion in species from insects to humans.

Observer age and the social transmission of attractiveness in humans: Younger women are more influenced by the choices of popular others than older women

Being paired with an attractive partner increases perceptual judgements of attractiveness in humans. We tested experimentally for prestige bias, whereby individuals follow the choices of prestigious others. Women rated the attractiveness of photographs of target males which were paired with either popular or less popular model female partners. We found that pairing a photo of a man with a woman presented as his partner positively influenced the attractiveness of the man when the woman was presented as more popular (Experiment 1). Further, this effect was stronger in younger participants compared to older participants (Experiment 1). Reversing the target and model such that women were asked to rate women paired with popular and less popular men revealed no effect of model popularity and this effect was unrelated to participant age (Experiment 2). An additional experiment confirmed that participant age and not stimulus age primarily influenced the tendency to follow others' preferences in Experiment 1 (Experiment 3). We also confirmed that our manipulations of popularity lead to variation in rated prestige (Experiment 4). These results suggest a sophisticated model-based bias in social learning whereby individuals are most influenced by the choices of those who have high popularity/prestige. Furthermore, older individuals moderate their use of such social information and so this form of social learning appears strongest in younger women.

End state copying by humans (Homo sapiens): implications for a comparative perspective on cumulative culture

It has been proposed that the uniqueness of human cumulative culture may be attributable to humans' greater orientation toward copying the process of behavior (imitation), as compared with the products (emulation), resulting in particularly high fidelity transmission. Following from previous work indicating that adult human participants can exhibit cumulative learning on the basis of product copying alone, we now investigate whether such learning involves high fidelity transmission. Eighty adult human (Homo sapiens) participants were presented with a task previously shown to elicit cumulative learning under experimental conditions, which involved building a tower from spaghetti and modeling clay. Each participant was shown two completed towers, ostensibly built by previous participants, but actually built to prespecified designs by the experimenter. This end state information was provided either in the form of photographs, or the presence of actual towers. High fidelity matching to these end states was apparent in both demonstration conditions, even for a design that was demonstrably suboptimal with regard to the goal of the task (maximizing tower height). We conclude that, although high fidelity transmission is likely to be implicated in cumulative culture, action copying is not always necessary for this to occur. Furthermore, since chimpanzees apparently copy behavioral processes and well as products, and also transmit behavior with high fidelity, the stark absence of unequivocal examples of cumulative culture in nonhumans may be attributable to factors other than imitative ability.

Effects of partner beauty on opposite-sex attractiveness judgments

Many studies show mate choice copying effects on mate preferences in non-human species in which individuals follow or copy the mate choices of same-sex conspecifics. Recent studies suggest that social learning also influences mate preferences in humans. Studies on heterosexual humans have focused on rating the attractiveness of potential mates (targets) presented alongside individuals of the opposite sex to the target (models). Here, we examined several different types of pairing to examine how specific social learning is to mate preferences. In Study 1, we replicated a previous effect whereby target faces of the opposite sex to the subject were rated as more attractive when paired with attractive than unattractive partner models of the same sex as the subject. Using the same paired stimuli, Study 2 demonstrated no effect of a paired model if subjects were asked to rate targets who were the same sex as themselves. In Study 3, we used pairs of the same sex, stating the pair were friends, and subjects rated targets of the opposite sex to themselves. Attractive models decreased targets' attractiveness, opposite to the effect in Study 1. Finally, Study 4 examined if attractive versus unattractive non-face stimuli might influence attraction. Unlike in Study 1, pairing with attractive stimuli either had no effect or decreased the attractiveness of paired target face images. These data suggest that social transmission of preferences via pairing with attractive/unattractive images is relatively specific to learning about mate preferences but does not influence attractiveness judgments more generally.

Social learning and human mate preferences: a potential mechanism for generating and maintaining between-population diversity in attraction

Inspired by studies demonstrating mate-choice copying effects in non-human species, recent studies of attractiveness judgements suggest that social learning also influences human preferences. In the first part of our article, we review evidence for social learning effects on preferences in humans and other animals. In the second part, we present new empirical evidence that social learning not only influences the attractiveness of specific individuals, but can also generalize to judgements of previously unseen individuals possessing similar physical traits. The different conditions represent different populations and, once a preference arises in a population, social learning can lead to the spread of preferences within that population. In the final part of our article, we discuss the theoretical basis for, and possible impact of, biases in social learning whereby individuals may preferentially copy the choices of those with high status or better access to critical information about potential mates. Such biases could mean that the choices of a select few individuals carry the greatest weight, rapidly generating agreement in preferences within a population. Collectively, these issues suggest that social learning mechanisms encourage the spread of preferences for certain traits once they arise within a population and so may explain certain cross-cultural differences.

Comparative cultural cognition

Cultural learning is an adaptive mechanism which can lead to changes in behavior and cognition much faster than naturally selected genetic change. Although social learning is prevalent in many species, the capacity for significant cumulative culture remains restricted to humans. This capacity has been a driving force behind the evolution of complexity in our technologies and societies, and has allowed us to become the most widespread mammal on earth. The comparative study of cultural cognition assesses where important differences lie between species. A combination of observational studies in the wild, experimental studies in captivity, and field experiments together provide the most comprehensive methods with which to tackle the question. Copyright © 2009 John Wiley & Sons, Ltd. For further resources related to this article, please visit the WIREs website.

Social learning mechanisms and cumulative cultural evolution. Is imitation necessary?

Cumulative cultural evolution has been suggested to account for key cognitive and behavioral attributes that distinguish modern humans from their anatomically similar ancestors, but researchers have yet to establish which cognitive mechanisms are responsible for this kind of learning and whether they are unique to humans. Here, we show that human participants' cumulative learning is not always reliant on sources of social information commonly assumed to be essential. Seven hundred participants were organized into 70 microsocieties and completed a task involving building a paper airplane. We manipulated the availability of opportunities for imitation (reproducing actions), emulation (reproducing end results), and teaching. Each condition was independently sufficient for participants to show cumulative learning. Because emulative learning can elicit cumulative culture on this task, we conclude that accounts of the unusual complexity of human culture in terms of species-unique learning mechanisms do not currently provide complete explanations and that other factors may be involved.

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.

Artificially generated cultural variation between two groups of captive monkeys, Colobus guereza kikuyuensis

The majority of studies of social learning in primates have tested subjects in isolation and investigated the effects of learning over very short periods of time. We aimed to test for social learning in two social groups of colobus monkeys, Colobus guereza kikuyuensis. Subjects were shown video footage of familiar monkeys either pushing or pulling a plastic flap to obtain a food reward, while they were given simultaneous access to the same apparatus. Action frequencies showed a significant difference between the two groups, with the pull group performing a higher proportion of pulls to pushes, compared with the push group. Copying persisted even in later sessions during which the demonstration footage was not being shown. We conclude that we successfully generated two contrasting behavioural traditions in these groups of monkeys. We do not know how long this contrast in behaviour would have persisted had we been able to continue testing for an even longer period of time, but further studies using similar designs and even longer test periods would have the power to confirm whether stable behavioural variation can be sustained between groups of monkeys, supported by social transmission.

Visual co-orientation and expectations about attentional orientation in pileated gibbons (Hylobates pileatus)

This study investigated attentional processes in a sample of captive gibbons. An initial aim of the research was to examine subjects' ability to co-orient with photographic images of both conspecific and human models. The gibbons' expectancies about the focus of another's attention was then also assessed, with an expectancy violation paradigm revealing subjects' sensitivity to an incompatibility between visual orientation and the position of a target object. The gibbons were exposed to two conditions; consistent sequences in which the stimulus individual directed attention towards a target object, and inconsistent sequences in which the model's attentional focus was incompatible with the location of this article. Analyses of the subjects' responses were made according to the direction of gazes and the time spent inspecting the depicted model in each of these conditions. The results reveal a tendency for visual co-orientation with both conspecific and human models, suggesting that gibbons are competent in detecting the visual orientation of other species as well as their own. Furthermore, the subjects' tendency to look longer and check back to the depicted model in response to violations in the relationship between an agent and object (target appearing in an opposite direction to model's gaze), suggests that they possess some knowledge of how visual gaze direction relates to external stimuli.

Testing for social learning and imitation in common marmosets, Callithrix jacchus , using an artificial fruit

We tested for social learning and imitation in common marmosets using an artificial foraging task and trained conspecific demonstrators. We trained a demonstrator marmoset to open an artificial fruit, providing a full demonstration of the task to be learned. Another marmoset provided a partial demonstration, controlling for stimulus enhancement effects, by eating food from the outside of the apparatus. We thus compared three observer groups, each consisting of four animals: those that received the full demonstration, those that received the partial demonstration, and a control group that saw no demonstration prior to testing. Although none of the observer marmosets succeeded in opening the artificial fruit during the test periods, there were clear effects of demonstration type. Those that saw the full demonstration manipulated the apparatus more overall, whereas those from the control group manipulated it the least of the three groups. Those from the full-demonstration group also contacted the particular parts of the artificial fruit that they had seen touched (localised stimulus enhancement) to a greater extent than the other two groups. There was also an interaction between the number of hand and mouth touches made to the artificial fruit for the full- and partial-demonstration groups. Whether or not these data represent evidence for imitation is discussed. We also propose that the clear differences between the groups suggest that social learning mechanisms provide real benefits to these animals in terms of developing novel food-processing skills analogous to the one presented here.

Evolutionary perspectives on imitation: is a comparative psychology of social learning possible?

Studies of imitation in animals have become numerous in recent times, but do they contribute to a comparative psychology of social learning? We review this burgeoning field to identify the problems and prospects for such a goal. Difficulties of two main kinds are identified. First, researchers have tackled questions about social learning from at least three very different theoretical perspectives, the "phylogenetic", "animal model", and "adaptational". We examine the conflicts between them and consider the scope for integration. A second difficulty arises in the methodological approaches used in the discipline. In relation to one of these - survey reviews of published studies - we tabulate and compare the contrasting conclusions of nine articles that together review 36 studies. The basis for authors' disagreements, including the matters of perceptual opacity, novelty, sequential structure, and goal representation, are examined. In relation to the other key method, comparative experimentation, we identify 12 studies that have explicitly compared species' imitative ability on similar tasks. We examine the principal problems of comparing like with like in these studies and consider solutions, the most powerful of which we propose to be the use of a systematic range of task designs, rather than any single "gold standard" task.

Effect of active limb movements on symptoms in patients with low back pain

STUDY DESIGN

A descriptive, correlational study of patients with mechanical low back pain (LBP).

OBJECTIVES

To assess the effect of active limb movements on symptoms in patients with LBP and to examine the relationship between symptoms with limb movements and select patient characteristics.

BACKGROUND

Limb movements result in forces applied to the spine and, thus, may be important in the examination and treatment of patients with LBP.

METHODS AND MEASURES

A total of 188 people with LBP, 84 men and 104 women, participated in a standardized examination. Six of the items required patients to move their limbs and note LBP symptoms as increased, remained the same, or decreased. The prevalence of various symptom responses with each limb movement test was calculated. Relationships between patient characteristics and reports of increased symptoms were examined with Cochran's linear trend statistic and the Spearman and Pearson correlation coefficients. Differences in characteristics of patients with and without increased symptoms were examined with chi2 test, Mann-Whitney U test, or Student's t test for independent groups.

RESULTS

An increase in symptoms was reported by 149 patients with at least 1 of the limb movement tests, and 3 of the patients reported a decrease in symptoms. Across the patient sample, the mean number of limb movement tests for which symptoms were reported as increased was 2.30 +/- 1.64. Patients with an increase in symptoms reported higher average pain intensity the week prior to the examination (median = 2; range: 1-5) and higher functional disability (mean = 0.25; SD = 0.15) than those without a change in symptoms (pain intensity: median = 1; range: 0-2 and functional disability: mean = 0.16; SD = 0.12). The correlation between the number of increased symptoms and the person's average pain intensity was r = 0.23; the correlation with the functional disability score was r = 0.36. Patients with a history of LBP tended to report an increase in symptoms with more of the limb movement tests (mean = 3.5; SD = 1.40) than those without a previous history of LBP (mean = 2.0; SD = 1.11).

CONCLUSIONS

Active limb movements performed during the examination primarily resulted in increased LBP symptoms. The presence and number of increased symptoms with the active limb movements was related to the patient's report of average pain intensity and functional disability. Tests of symptoms with active limb movements may provide insight into factors contributing to a LBP problem, as well as information to guide the treatment of patients with LBP.

Potential effects of forest fire and storm flow on total mercury and methylmercury in sediments of an arid-lands reservoir

A study was conducted from July 1995 to June 1996 to examine the spatial and temporal changes of mercury concentrations in sediments of an arid-lands reservoir. Prior to the first sample collection in July, a forest fire burned 2930 ha of mixed conifer and ponderosa pine in the watershed of Caballo Reservoir in south-central New Mexico. The fire was eventually extinguished by summer rains and storm runoff resulting in the mobilization and transport of charred vegetative material into an intermittent tributary (Palomas Creek) that drains the watershed into Caballo Reservoir. Concentrations of total mercury (THg), monomethlymercury (MMHg), and total organic carbon (TOC) in surficial sediments revealed fire, followed by storm runoff, enhanced the transport of mercury and organic matter to the reservoir. Concentrations of THg in sediments increased from 7.5 etag/g in July to 46.1 etag/g by November 1995 at one site (Palomas) nearest the outflow of Palomas Creek. No other spatial or temporal trends were observed for THg at other sites throughout the remainder of the study. Concentrations of MMHg in sediments at the Palomas site increased from 0.428 etag/g in July to 12.46 etag/g by October 1995 compared to concentrations in sediments at the remaining sites which ranged from 0.11 to 1.50 etag/g throughout the study. The ratio of MMHg to THg (a gross index of methylation activity) was greatest in sediments from the Palomas site (5.4-33.8%) compared to the remaining sites (0.01-3.60%). The ratio was mirrored by elevated TOC in sediments at the Palomas site (2.5-11.8%) that remained elevated throughout the study. Fire and subsequent late-summer rains may have had a twofold effect on mercury concentrations in Caballo Reservoir. The storm-driven runoff following the forest fire carried mercury complexed to organic matter which resulted in elevated levels of mercury as well as providing a carbon source for microbial methylation processes in sediment.

Discharge of methylmercury-enriched hypolimnetic water from a stratified reservoir

A study conducted from July 1995 to June 1996 examining spatial and temporal distribution of mercury (Hg) at the Caballo Reservoir, New Mexico, revealed that the highest levels of methylmercury (MMHg) occurred in both the inlet and the Rio Grande upstream of the reservoir. As a result, a second study was designed to identify possible sources of the elevated levels of MMHg, and to determine if water discharged from the Elephant Butte Reservoir upstream could be a primary source. In July 1996, as anoxia began to develop in the hypolimnion of the Elephant Butte Reservoir, surface water MMHg concentrations were below the MDL of 0.018 ng/l while water discharged into the tailrace was 0.149 ng/l MMHg. By September 1996, when the anoxic hypolimnion spanned 60% of the total reservoir depth, surface water MMHg was still below the MDL, while discharge water had increased to 1.144 ng/l MMHg. Following reservoir turnover in November 1996, surface water increased to 0.264 ng/l MMHg while discharge water decreased to 0.420 ng/l MMHg. By January 1997, MMHg in the tailrace decreased to pre-stratification levels, and both surface water and discharge water reached similar MMHg levels until the onset of summer stratification in July 1997. This trend was repeated the following year when MMHg concentrations in the tailrace increased from 0.190 ng/l in August 1997 to 1.240 ng/l in September 1997. In addition, vertical profile sampling of the reservoir from August 1997 to September 1997 showed a buildup of MMHg in the anoxic hypolimnion which coincided with increasing levels of MMHg discharged into the tailrace. During the course of this study the single largest contribution of MMHg to the river below the reservoir was from water released through the dam during the fall months of the year.

Mercury distribution in blood, tissues, and feathers of double-crested cormorant nestlings from arid-lands reservoirs in south central New Mexico

Eggs, blood, liver, muscle, and feathers were analyzed for concentrations of total mercury in double-crested cormorant (Phalacrocorax auritus) nestlings from two reservoirs in south central New Mexico. Total mercury concentrations among eggs, tissues, and feathers were not significantly correlated. Concentrations of total mercury averaged 0.40 microg/g in liver and 0.18 microg/g in muscle tissues in both populations of nestlings. There were no significant changes in concentrations of total mercury in whole blood of nestlings collected 7-10 days and 17-22 days posthatch in Caballo Reservoir (0.36 microg/g and 0.39 microg/g, respectively) and in Elephant Butte Reservoir (0.36 microg/g and 0.34 microg/g, respectively). Total mercury concentrations were similar for blood, muscle, and liver in nestlings for both reservoirs. Total mercury concentrations were higher in eggs and tail, primary, and secondary feathers from nestlings at Caballo Reservoir compared to Elephant Butte Reservoir. Although there were no differences in concentrations of total mercury in fishes between the two reservoirs, bioaccumulation and biomagnification was evident in planktivorous and piscivorous fishes. The data demonstrate that feather analysis may not be a good predictor of tissue burden in nestlings from regions of low contamination.

Reliability of physical examination items used for classification of patients with low back pain

BACKGROUND AND PURPOSE

The purpose of this study was to examine the interrater reliability of measurements obtained by examiners administering tests proposed to be important for classifying low back pain (LBP) problems.

SUBJECTS

Ninety-five subjects with LBP (41 men, 54 women) and 43 subjects without LBP (17 men, 26 women) were examined by 5 therapists trained in the techniques used.

METHODS

A manual was developed by the first author that described the clinical examination procedures. The therapists were trained by the first author in the test procedures and definitions. The training included instruction through videotapes, practice and a written examination. Each examination was conducted by a pair of therapists. Within a pair, a therapist was the primary examiner for half of the subjects and an observer was the primary examiner for half of the subjects. Examination findings were recorded independently, without discussion.

RESULTS

Percentage of agreement and generalized kappa coefficients were used to analyzed the data. Kappa values were > or = .75 for all 28 items related to the symptoms elicited and > or = .40 for 72% of the 25 items related to alignment and movement.

CONCLUSION AND DISCUSSION

The results suggest that experienced therapist who had trained together were able to agree on the results of examinations and obtain an acceptable level of reliability. Future work should focus on testing of reliability when more than one therapist performs the examination and when therapist not trained by the test developer to administer the examination perform the tests. [Van Dillen LR, Sahrmann SA, Norton BJ, et al. Reliability of physical examination items used for classification of patients with low back pain.

Effects of lead on the growth and delta-aminolevulinic acid dehydratase activity of juvenile rainbow trout, Oncorhynchus mykiss

Activity of delta-aminolevulinic acid dehydratase (ALA-D) in blood and organs is a biomarker of lead (Pb) contamination in fish. Because current methods cannot measure the bioavailability of Pb, this biomarker may predict exposure more accurately than analysis of Pb concentrations in water. Juvenile fish are generally more sensitive to Pb than adult fish, but due to their small size, analysis of ALA-D in blood and individual organs is difficult. By modifying the erythrocyte ALA-D procedure, we developed a method to measure ALA-D activity on the supernatant from the tissue homogenate of whole fish (juvenile rainbow trout, Oncorhynchus mykiss). Significant decreases in the activity of ALA-D in rainbow trout were observed after a 29-day exposure to 121 and 201 microg Pb liter(-1), but not after exposure to 29 or 48 microg Pb liter(-1). Pb also significantly reduced growth in fish exposed to 201 microg Pb liter(-1).

Esophageal dysphagia as the sole symptom in type I Chiari malformation

Chiari malformation, also called Arnold-Chiari deformities, are rare hindbrain herniations that may present in children or adults. The most common symptoms include headache, syncope, disordered eye movement, sensory loss, weakness, and cerebellar features such as ataxia. Dysphagia occurs in 5-15% of patients, although only a few reports describe dysphagia as the only presenting symptom. We report a case of a 27-year-old woman who presented with a three-year history of dysphagia, chest pain, and weight loss. Esophageal manometrics revealed markedly disordered esophageal motility and gastroesophageal reflux. Her symptoms failed to respond to high doses of omeprazole, prokinetics, and eventually surgical fundoplication. The subsequent onset of neurological symptoms led to the diagnosis of Chiari type I malformation. Following posterior craniotomy with decompression, her dysphagia and chest discomfort completely resolved. Repeat esophageal manometrics revealed complete resolution of prior abnormalities.

Muto ergo sum. Hepatitis B and the forces of evolution

The hepatitis B virus (HBV) polymerase has no editing function and thus frequently transcribes its template incorrectly to result in viral variants that go under the name of "mutants." These mutants may be viewed as part of a continuing Darwinian evolution of HBV with some survival benefit. They also result in unusual extrahepatic manifestations of HBV infection, which will doubtless continue to divert the hepatologist.

Distribution of cortisol among its free and protein-bound fractions in rainbow trout (Oncorhynchus mykiss): evidence of control by sexual maturation

1. Total cortisol concentrations did not differ in sexually matured female, male, and immature rainbow trout. 2. The per cent cortisol bound to a corticosteroid binding protein was greater in mature female fish (48.2%) than in mature male (16.0%) and immature fish (19.5%). 3. The mature female fish exhibited a lower percentage of free cortisol (21.8%) compared to mature males (44.8%) and immature fish (43.2%). 4. Parallel aspects of the teleostean cortisol binding-protein and the mammalian counterpart are compared and commented upon.