Social intelligence, innovation, and enhanced brain size in primates

A natural history of the human mind: tracing evolutionary changes in brain and cognition

Since the last common ancestor shared by modern humans, chimpanzees and bonobos, the lineage leading to Homo sapiens has undergone a substantial change in brain size and organization. As a result, modern humans display striking differences from the living apes in the realm of cognition and linguistic expression. In this article, we review the evolutionary changes that occurred in the descent of Homo sapiens by reconstructing the neural and cognitive traits that would have characterized the last common ancestor and comparing these with the modern human condition. The last common ancestor can be reconstructed to have had a brain of approximately 300-400 g that displayed several unique phylogenetic specializations of development, anatomical organization, and biochemical function. These neuroanatomical substrates contributed to the enhancement of behavioral flexibility and social cognition. With this evolutionary history as precursor, the modern human mind may be conceived as a mosaic of traits inherited from a common ancestry with our close relatives, along with the addition of evolutionary specializations within particular domains. These modern human-specific cognitive and linguistic adaptations appear to be correlated with enlargement of the neocortex and related structures. Accompanying this general neocortical expansion, certain higher-order unimodal and multimodal cortical areas have grown disproportionately relative to primary cortical areas. Anatomical and molecular changes have also been identified that might relate to the greater metabolic demand and enhanced synaptic plasticity of modern human brain's. Finally, the unique brain growth trajectory of modern humans has made a significant contribution to our species' cognitive and linguistic abilities.

Tool-use training in a species of rodent: the emergence of an optimal motor strategy and functional understanding

Background

Tool use is defined as the manipulation of an inanimate object to change the position or form of a separate object. The expansion of cognitive niches and tool-use capabilities probably stimulated each other in hominid evolution. To understand the causes of cognitive expansion in humans, we need to know the behavioral and neural basis of tool use. Although a wide range of animals exhibit tool use in nature, most studies have focused on primates and birds on behavioral or psychological levels and did not directly address questions of which neural modifications contributed to the emergence of tool use. To investigate such questions, an animal model suitable for cellular and molecular manipulations is needed.

Methodology/Principal Findings

We demonstrated for the first time that rodents can be trained to use tools. Through a step-by-step training procedure, we trained degus (Octodon degus) to use a rake-like tool with their forelimbs to retrieve otherwise out-of-reach rewards. Eventually, they mastered effective use of the tool, moving it in an elegant trajectory. After the degus were well trained, probe tests that examined whether they showed functional understanding of the tool were performed. Degus did not hesitate to use tools of different size, colors, and shapes, but were reluctant to use the tool with a raised nonfunctional blade. Thus, degus understood the functional and physical properties of the tool after extensive training.

Conclusions/Significance

Our findings suggest that tool use is not a specific faculty resulting from higher intelligence, but is a specific combination of more general cognitive faculties. Studying the brains and behaviors of trained rodents can provide insights into how higher cognitive functions might be broken down into more general faculties, and also what cellular and molecular mechanisms are involved in the emergence of such cognitive functions.

Animal innovation defined and operationalized

Innovation is a key component of most definitions of culture and intelligence. Additionally, innovations may affect a species' ecology and evolution. Nonetheless, conceptual and empirical work on innovation has only recently begun. In particular, largely because the existing operational definition (first occurrence in a population) requires long-term studies of populations, there has been no systematic study of innovation in wild animals. To facilitate such study, we have produced a new definition of innovation: Innovation is the process that generates in an individual a novel learned behavior that is not simply a consequence of social learning or environmental induction. Using this definition, we propose a new operational approach for distinguishing innovations in the field. The operational criteria employ information from the following sources: (1) the behavior's geographic and local prevalence and individual frequency; (2) properties of the behavior, such as the social role of the behavior, the context in which the behavior is exhibited, and its similarity to other behaviors; (3) changes in the occurrence of the behavior over time; and (4) knowledge of spontaneous or experimentally induced behavior in captivity. These criteria do not require long-term studies at a single site, but information from multiple populations of a species will generally be needed. These criteria are systematized into a dichotomous key that can be used to assess whether a behavior observed in the field is likely to be an innovation.

Sex-linked neuroanatomical basis of human altruistic cooperativeness

Human altruistic cooperativeness, one of the most important components of our highly organized society, is along with a greatly enlarged brain relative to body size a spectacular outlier in the animal world. The "social-brain hypothesis" suggests that human brain expansion reflects an increased necessity for information processing to create social reciprocity and cooperation in our complex society. The present study showed that the young adult females (n = 66) showed greater Cooperativeness as well as larger relative global and regional gray matter volumes (GMVs) than the matched males (n = 89), particularly in the social-brain regions including bilateral posterior inferior frontal and left anterior medial prefrontal cortices. Moreover, in females, higher cooperativeness was tightly coupled with the larger relative total GMV and more specifically with the regional GMV in most of the regions revealing larger in female sex-dimorphism. The global and most of regional correlations between GMV and Cooperativeness were significantly specific to female. These results suggest that sexually dimorphic factors may affect the neurodevelopment of these "social-brain" regions, leading to higher cooperativeness in females. The present findings may also have an implication for the pathophysiology of autism; characterized by severe dysfunction in social reciprocity, abnormalities in social-brain, and disproportionately low probability in females.

Evolutionary biology of insect learning

Learning and memory, defined as the acquisition and retention of neuronal representations of new information, are ubiquitous among insects. Recent research indicates that a variety of insects rely extensively on learning for all major life activities including feeding, predator avoidance, aggression, social interactions, and sexual behavior. There is good evidence that individuals within an insect species exhibit genetically based variation in learning abilities and indirect evidence linking insect learning to fitness. Although insects rely on innate behavior to successfully manage many types of variation and unpredictability, learning may be superior to innate behavior when dealing with features unique to time, place, or individuals. Among insects, social learning , which can promote the rapid spread of novel behaviors, is currently known only from a few well-studied examples in social Hymenoptera. The prevalence and importance of social learning in insects are still unknown. Similarly, we know little about ecological factors that may have promoted enhanced learning abilities in insects, and whether learning has significantly contributed to speciation in insects.

The human dimension: how the prefrontal cortex modulates the subcortical fear response

Numerous studies suggest that the amygdala is critical for the acquisition and expression of fear. Conditioned fear in animals has been considered a good model for human anxiety disorders, but animal models of anxiety have several limitations. Conditioned fear in animals can be directed to a specific stressor and is easily extinguished. Furthermore, animals do not seem to be able to develop the capacity to worry excessively about the future. While animal models are useful and can demonstrate psychiatric illnesses, they do not completely mimic the complex cognitive processes that occur in anxious humans. Thus, we hypothesize that human anxiety disorders are caused at least in part by differential activity in the prefrontal cortex, the brain region that most separates us from our nearest genetic neighbors. The human prefrontal cortex has not only been shown to be more developed than that of other mammals, but it also has unique morphology and gene expression. Neuroimaging studies repeatedly show abnormalities in the prefrontal cortex in anxious individuals. Thus, we suggest that the very same cortical complexity that allows us to produce a vibrant culture is also the seat of anxiety disorders. Interestingly, preclinical studies have shown that the prefrontal cortex inhibits the amygdala. There appears to be a distinction between two classes of anxiety disorders. Those disorders involving intense fear and panic--panic disorder, post-traumatic stress disorder, and phobias--seem to be characterized by an underactivity of the prefrontal cortex, thus disinhibiting the amygdala. Disorders such as generalized anxiety disorder and obsessive-compulsive disorder, which involve worry and rumination, on the other hand, seem to be characterized by an overactivity of the prefrontal cortex. Studies of prefrontal cortical function in psychiatric illness should be a fruitful method for identifying effective treatment approaches.

Life history costs and benefits of encephalization: a comparative test using data from long-term studies of primates in the wild

The correlation between brain size and life history has been investigated in many previous studies, and several viable explanations have been proposed. However, the results of these studies are often at odds, causing uncertainties about whether these two character complexes underwent correlated evolution. These disparities could arise from the mixture of wild and captive values in the datasets, potentially obscuring real relationships, and from differences in the methods of controlling for phylogenetic non independence of species values. This paper seeks to resolve these difficulties by (1) proposing an overarching hypothesis that encompasses many of the previously proposed hypotheses, and (2) testing the predictions of this hypothesis using rigorously compiled data and utilizing multiple methods of analysis. We hypothesize that the adaptive benefit of increased encephalization is an increase in reproductive lifespan or efficiency, which must be sufficient to outweigh the costs due to growing and maturing the larger brain. These costs and benefits are directly reflected in the length of life history stages. We tested this hypothesis on a wide range of primate species. Our results demonstrate that encephalization is significantly correlated with prolongation of all stages of developmental life history except the lactational period, and is significantly correlated with an extension of the reproductive lifespan. These results support the contention that the link between brain size and life history is caused by a balance between the costs of growing a brain and the survival benefits the brain provides. Thus, our results suggest that the evolution of prolonged life history during human evolution is caused by increased encephalization.

On the concept of animal innovation and the challenge of studying innovation in the wild

The commentaries have both drawn out the implications of, and challenged, our definition and operationalization of innovation. In this response, we reply to these concerns, discuss the differences between our operationalization and the preexisting operationalization if innovation, and make suggestions for the advancement of the challenging and exciting field of animal innovation.

Genetic assimilation of behaviour does not eliminate learning and innovation

Ramsey et al. attempt to clarify methodological issues for identifying innovative behaviour. Their effort is seriously weakened by an underlying presumption that the behavior of primates is generally learned and that of non-primates is generally “innate.” This presumption is based on a poor grasp of the non-primate literature and a flawed understanding of how learned behaviour is genetically assimilated.

Environmentally invoked innovation and cognition

Behavioral innovations induced by the social or physical environment are likely to be of great functional and evolutionary importance, and thus warrant serious attention. Innovation provides a process by which animals can adjust to changed environments. Despite this apparent adaptive advantage, it is not known whether innovative propensities are adaptive specializations. Furthermore, the varied psychological processes underlying innovation remain poorly understood.

Cetaceans have complex brains for complex cognition

A group of eminent cetacean researchers respond to headlines charging that dolphins might be "flippin' idiots". They examine behavioural, anatomical and evolutionary data to conclude that the large brain of cetaceans evolved to support complex cognitive abilities.

The evolution of the social brain: anthropoid primates contrast with other vertebrates

The social brain hypothesis argues that large brains have arisen over evolutionary time as a response to the social and ecological conflicts inherent in group living. We test predictions arising from the hypothesis using comparative data from birds and four mammalian orders (Carnivora, Artiodactyla, Chiroptera and Primates) and show that, across all non-primate taxa, relative brain size is principally related to pairbonding, but with enduring stable relationships in primates. We argue that this reflects the cognitive demands of the behavioural coordination and synchrony that is necessary to maintain stable pairbonded relationships. However, primates differ from the other taxa in that they also exhibit a strong effect of group size on brain size. We use data from two behavioural indices of social intensity (enduring bonds between group members and time devoted to social activities) to show that primate relationships differ significantly from those of other taxa. We suggest that, among vertebrates in general, pairbonding represents a qualitative shift from loose aggregations of individuals to complex negotiated relationships, and that these bonded relationships have been generalized to all social partners in only a few taxa (such as anthropoid primates).

Understanding primate brain evolution

We present a detailed reanalysis of the comparative brain data for primates, and develop a model using path analysis that seeks to present the coevolution of primate brain (neocortex) and sociality within a broader ecological and life-history framework. We show that body size, basal metabolic rate and life history act as constraints on brain evolution and through this influence the coevolution of neocortex size and group size. However, they do not determine either of these variables, which appear to be locked in a tight coevolutionary system. We show that, within primates, this relationship is specific to the neocortex. Nonetheless, there are important constraints on brain evolution; we use path analysis to show that, in order to evolve a large neocortex, a species must first evolve a large brain to support that neocortex and this in turn requires adjustments in diet (to provide the energy needed) and life history (to allow sufficient time both for brain growth and for 'software' programming). We review a wider literature demonstrating a tight coevolutionary relationship between brain size and sociality in a range of mammalian taxa, but emphasize that the social brain hypothesis is not about the relationship between brain/neocortex size and group size per se; rather, it is about social complexity and we adduce evidence to support this. Finally, we consider the wider issue of how mammalian (and primate) brains evolve in order to localize the social effects.

Dolphin social intelligence: complex alliance relationships in bottlenose dolphins and a consideration of selective environments for extreme brain size evolution in mammals

Bottlenose dolphins in Shark Bay, Australia, live in a large, unbounded society with a fission-fusion grouping pattern. Potential cognitive demands include the need to develop social strategies involving the recognition of a large number of individuals and their relationships with others. Patterns of alliance affiliation among males may be more complex than are currently known for any non-human, with individuals participating in 2-3 levels of shifting alliances. Males mediate alliance relationships with gentle contact behaviours such as petting, but synchrony also plays an important role in affiliative interactions. In general, selection for social intelligence in the context of shifting alliances will depend on the extent to which there are strategic options and risk. Extreme brain size evolution may have occurred more than once in the toothed whales, reaching peaks in the dolphin family and the sperm whale. All three 'peaks' of large brain size evolution in mammals (odontocetes, humans and elephants) shared a common selective environment: extreme mutual dependence based on external threats from predators or conspecific groups. In this context, social competition, and consequently selection for greater cognitive abilities and large brain size, was intense.

Evolution in the Social Brain

The evolution of unusually large brains in some groups of animals, notably primates, has long been a puzzle. Although early explanations tended to emphasize the brain's role in sensory or technical competence (foraging skills, innovations, and way-finding), the balance of evidence now clearly favors the suggestion that it was the computational demands of living in large, complex societies that selected for large brains. However, recent analyses suggest that it may have been the particular demands of the more intense forms of pairbonding that was the critical factor that triggered this evolutionary development. This may explain why primate sociality seems to be so different from that found in most other birds and mammals: Primate sociality is based on bonded relationships of a kind that are found only in pairbonds in other taxa.

Sociality, Evolution and Cognition

Variations in brain size and proportions can be linked to the cognitive capacities of different animal species, and correlations with ecology may give clues to the evolutionary origins of these specializations. Much recent evidence has implicated the social domain as a major challenge driving increases in problem-solving abilities of mammals. However, the methods of measurement available to researchers are often indirect and sometimes appear to give conflicting answers, and other intellectual challenges may also have been influential in cognitive evolution. While the cause of an evolutionary increase in intelligence may be domain-specific (sociality, for example), and the brain specialization that results may largely implicate a single perceptual system, such as vision, the intelligence shown in consequence can be very 'general-purpose' (as in primates and some avian taxa). Future research needs to get beyond vague ascription of 'greater intelligence' or 'faster learning' towards a precise account of the cognitive mechanisms that underlie particular mental skills in different species; that will allow theory-testing against data from complex, natural situations as well as from the laboratory, on a common metric.

Defining and detecting innovation: Are cognitive and developmental mechanisms important?

Although the authors' ingenuity in identifying criteria for innovation for field studies is appealing, most field studies will lack adequate data. Additionally, their definition does not clearly distinguish innovation from individual learning and is vague about cognitive mechanisms involved. We suggest that developmental data are essential to identifying the causes and consequences of learning new behaviors.

Objectivism should not be a casualty of innovation's operationalization

We agree with Ramsey et al. regarding the need for new methods and concepts in the study of innovation, and welcome their initiative, but are concerned that their operationalization is over-reliant on subjective judgements.

Do bowerbirds exhibit cultures?

Definitions of what features constitute cultural behaviour, and hence define cultures are numerous. Many seem designed to describe those aspects of human behaviour which set us apart from other animals. A broad definition prescribing that the behaviour is: learned; learned socially; normative and collective is considered to apply to several species of great ape. In this paper, I review observations and experiments covering a suite of different behavioural characteristics displayed in members of the bowerbird family (Ptilonorhynchidae) and ask whether they fulfil these criteria. These include vocalisations, bower design, decoration use, bower orientation and display movements. Such a range of behaviours refutes the suggestion that these species are "one-trick ponies"--a criticism that is often levelled at claims for culture in non-primate species. I suggest that, despite a paucity of data in comparison with primate studies, it could be argued that bowerbirds may be considered to fulfil the same criteria on which we base our use of the term culture when applied to our close relatives, the great apes. If bowerbirds do have cultures, then their unusual natural history makes them a highly tractable system in which questions of social learning and culture can be tackled.

Overall Brain Size, and Not Encephalization Quotient, Best Predicts Cognitive Ability across Non-Human Primates

For over a century, various neuroanatomical measures have been employed as assays of cognitive ability in comparative studies. Nevertheless, it is still unclear whether these measures actually correspond to cognitive ability. A recent meta-analysis of cognitive performance of a broad set of primate species has made it possible to provide a quantitative estimate of general cognitive ability across primates. We find that this estimate is not strongly correlated with neuroanatomical measures that statistically control for a possible effect of body size, such as encephalization quotient or brain size residuals. Instead, absolute brain size measures were the best predictors of primate cognitive ability. Moreover, there was no indication that neocortex-based measures were superior to measures based on the whole brain. The results of previous comparative studies on the evolution of intelligence must be reviewed with this conclusion in mind.

Quality of life and the evolution of the brain

The dual problem of explaining brain evolution and the way in which it has led to wide species differences in behaviour and physiology has often appeared intractable to scientists. The main limiting factor is that we do not understand enough about how brains work to appreciate why gross or fine morphological differences can lead to the considerable across- as well as within-species differences in behaviour. Even at a molecular level, while two-thirds of our genes are involved in regulating brain function, there is a high degree of homology within different phyla. In the context of quality of life (QoL), arguably the most important consideration is that the brain you have evolved is adapted to the environment you are living in and is capable of generating ‘conscious’ experience. When that environment is radically altered, issues arise regarding whether there is sufficient adaptability to cope and the extent to which mental as well as physical suffering might be experienced as a consequence. At the other end of the spectrum there is the question of how enriched social and physical environments might enhance QoL through promoting positive affect. Here I will discuss potential functional contributions of differences in brain size and organisation and the impact of experience. I will mainly focus on mental functioning and show particularly that capacities for consciousness, emotional experience, social interaction and cognition and behavioural flexibility are likely to be widespread in other animal species, even if less developed than in humans.

Social intelligence, human intelligence and niche construction

This paper is about the evolution of hominin intelligence. I agree with defenders of the social intelligence hypothesis in thinking that externalist models of hominin intelligence are not plausible: such models cannot explain the unique cognition and cooperation explosion in our lineage, for changes in the external environment (e.g. increasing environmental unpredictability) affect many lineages. Both the social intelligence hypothesis and the social intelligence-ecological complexity hybrid I outline here are niche construction models. Hominin evolution is hominin response to selective environments that earlier hominins have made. In contrast to social intelligence models, I argue that hominins have both created and responded to a unique foraging mode; a mode that is both social in itself and which has further effects on hominin social environments. In contrast to some social intelligence models, on this view, hominin encounters with their ecological environments continue to have profound selective effects. However, though the ecological environment selects, it does not select on its own. Accidents and their consequences, differential success and failure, result from the combination of the ecological environment an agent faces and the social features that enhance some opportunities and suppress others and that exacerbate some dangers and lessen others. Individuals do not face the ecological filters on their environment alone, but with others, and with the technology, information and misinformation that their social world provides.

The evolution of animal 'cultures' and social intelligence

Decades-long field research has flowered into integrative studies that, together with experimental evidence for the requisite social learning capacities, have indicated a reliance on multiple traditions ('cultures') in a small number of species. It is increasingly evident that there is great variation in manifestations of social learning, tradition and culture among species, offering much scope for evolutionary analysis. Social learning has been identified in a range of vertebrate and invertebrate species, yet sustained traditions appear rarer, and the multiple traditions we call cultures are rarer still. Here, we examine relationships between this variation and both social intelligence--sophisticated information processing adapted to the social domain--and encephalization. First, we consider whether culture offers one particular confirmation of the social ('Machiavellian') intelligence hypothesis that certain kinds of social life (here, culture) select for intelligence: 'you need to be smart to sustain culture'. Phylogenetic comparisons, particularly focusing on our own study animals, the great apes, support this, but we also highlight some paradoxes in a broader taxonomic survey. Second, we use intraspecific variation to address the converse hypothesis that 'culture makes you smart', concluding that recent evidence for both chimpanzees and orangutans support this proposition.

Socially intelligent robots: dimensions of human-robot interaction

Social intelligence in robots has a quite recent history in artificial intelligence and robotics. However, it has become increasingly apparent that social and interactive skills are necessary requirements in many application areas and contexts where robots need to interact and collaborate with other robots or humans. Research on human-robot interaction (HRI) poses many challenges regarding the nature of interactivity and 'social behaviour' in robot and humans. The first part of this paper addresses dimensions of HRI, discussing requirements on social skills for robots and introducing the conceptual space of HRI studies. In order to illustrate these concepts, two examples of HRI research are presented. First, research is surveyed which investigates the development of a cognitive robot companion. The aim of this work is to develop social rules for robot behaviour (a 'robotiquette') that is comfortable and acceptable to humans. Second, robots are discussed as possible educational or therapeutic toys for children with autism. The concept of interactive emergence in human-child interactions is highlighted. Different types of play among children are discussed in the light of their potential investigation in human-robot experiments. The paper concludes by examining different paradigms regarding 'social relationships' of robots and people interacting with them.

Response toward novel stimuli in a group of tufted capuchins (Cebus libidinosus) in Brasília National Park, Brazil

We investigated responses toward novel foods and novel objects by wild capuchins that routinely exploit visitors' foods in Brasília National Park. Given the capuchins' daily exposure to human foods and objects, we expected them to be more explorative toward novel foods and objects compared to capuchins that are not habituated to visitors. However, since the safety and palatability of potential foods have to be learned, we also expected the capuchins to be cautious about eating novel foods, as has been reported for wild and captive capuchins. Stimuli were presented on a platform in four experimental conditions: familiar food (FF), novel food (NF), familiar food plus novel object (FF+O), and novel food plus novel object (NF+O). Latencies to approach and contact the platform, and to approach and to ingest food did not differ across conditions. Nevertheless, the capuchins were significantly more responsive (measured in terms of interest, manipulation, etc.) toward familiar foods than novel foods, and ate significantly more of the former. In other words, their explorative response toward novel foods led to little consumption. Our results do not support the "readiness to eat" hypothesis, according to which a lower readiness to eat and food neophobia are the consequences of the presence of a distracting novel object. The finding that capuchins explore novel stimuli but remain cautious about eating novel foods supports the view that neophilia and neophobia are motivationally independent responses.

Big-brained birds survive better in nature

Big brains are hypothesized to enhance survival of animals by facilitating flexible cognitive responses that buffer individuals against environmental stresses. Although this theory receives partial support from the finding that brain size limits the capacity of animals to behaviourally respond to environmental challenges, the hypothesis that large brains are associated with reduced mortality has never been empirically tested. Using extensive information on avian adult mortality from natural populations, we show here that species with larger brains, relative to their body size, experience lower mortality than species with smaller brains, supporting the general importance of the cognitive buffer hypothesis in the evolution of large brains.

Developmental environment, cultural transmission, and mate choice copying

Using female mate choice copying as a rudimentary form of cultural transmission, this study provides evidence that social environment during development has a significant effect on the tendency to use culturally acquired information. Groups of newborn guppies (Poecilia reticulata) were raised for 35 days in 1 of 5 "developmental environments". Groups of 15 newborns were raised in pools with no adults (treatment 1), both adult male and female guppies (treatments 2 and 3), only adult females (treatment 4) or only adult males (treatment 5). Mature females raised in treatments 1 and 2, but not treatments 3, 4, and 5, copied the mate choice of others. Treatments 1 and 2 correspond to social structures that guppies experience during their development in the wild. Newborn guppies swim together in shoals (analogous to treatment 1). As they mature, juveniles join schools of adult males and females (analogous to treatments 2). At no time during the normal developmental process are juveniles found with males, but only unreceptive females (as was the case for long periods in treatment 3) or in the presence of adults of only one sex (analogous to treatments 4 and 5). As such, normal developmental environments prime guppies for cultural transmission, while unnatural environments fail to do so.

A critique of comparative studies of brain size

In recent years, there have been over 50 comparative analyses carried out in which social or ecological variables have been used to explain variation in whole brain size, or a part thereof, in a range of vertebrate species. Here, we review this body of work, pointing out that there are a number of substantial problems with some of the assumptions that underpin the hypotheses (e.g. what brain size means), with the data collection and with the ways in which the data are combined in the analyses. These problems are particularly apparent in those analyses in which attempts are made to correlate complex behaviour with parts of the brain that carry out multiple functions. We conclude that now is the time to substantiate these results with data from experimental manipulations.

Social learning and innovation are positively correlated in pigeons (Columba livia)

When animals show both frequent innovation and fast social learning, new behaviours can spread more rapidly through populations and potentially increase rates of natural selection and speciation, as proposed by A.C. Wilson in his behavioural drive hypothesis. Comparative work on primates suggests that more innovative species also show more social learning. In this study, we look at intra-specific variation in innovation and social learning in captive wild-caught pigeons. Performances on an innovative problem-solving task and a social learning task are positively correlated in 42 individuals. The correlation remains significant when the effects of neophobia on the two abilities are removed. Neither sex nor dominance rank are associated with performance on the two tasks. Free-flying flocks of urban pigeons are able to solve the innovative food-finding problem used on captive birds, demonstrating it is within the range of their natural capacities. Taken together with the comparative literature, the positive correlation between innovation and social learning suggests that the two abilities are not traded-off.

Where Evolutionary Psychology Meets Cognitive Neuroscience: A Précis to Evolutionary Cognitive Neuroscience

Cognitive neuroscience, the study of brain-behavior relationships, has long attempted to map the brain. The discipline is flourishing, with an increasing number of functional neuroimaging studies appearing in the scientific literature daily. Unlike biology and even psychology, the cognitive neurosciences have only recently begun to apply evolutionary meta-theory and methodological guidance. Approaching cognitive neuroscience from an evolutionary perspective allows scientists to apply biologically based theoretical guidance to their investigations and can be conducted in both humans and nonhuman animals. In fact, several investigations of this sort are underway in laboratories around the world. This paper and two new volumes ( Platek, Keenan, and Shackelford [Eds.], 2007 ; Platek and Shackelford [Eds.], under contract) represent the first formal attempts to document the burgeoning field of evolutionary cognitive neuroscience. Here, we briefly review the current state of the science of evolutionary cognitive neuroscience, the methods available to the evolutionary cognitive neuroscientist, and what we foresee as the future directions of the discipline.

Environmental Complexity and Social Organization Sculpt the Brain in Lake Tanganyikan Cichlid Fish

Complex brains and behaviors have occurred repeatedly within vertebrate classes throughout evolution. What adaptive pressures drive such changes? Both environmental and social features have been implicated in the expansion of select brain structures, particularly the telencephalon. East African cichlid fishes provide a superb opportunity to analyze the social and ecological correlates of neural phenotypes and their evolution. As a result of rapid, recent, and repeated radiations, there are hundreds of closely-related species available for study, with an astonishing diversity in habitat preferences and social behaviors. In this study, we present quantitative ecological, social, and neuroanatomical data for closely-related species from the (monophyletic) Ectodini clade of Lake Tanganyikan cichlid fish. The species differed either in habitat preference or social organization. After accounting for phylogeny with independent contrasts, we find that environmental and social factors differentially affect the brain, with environmental factors showing a broader effect on a range of brain structures compared to social factors. Five out of seven of the brain measures show a relationship with habitat measures. Brain size and cerebellar size are positively correlated with species number (which is correlated with habitat complexity); the medulla and olfactory bulb are negatively correlated with habitat measures. The telencephalon shows a trend toward a positive correlation with rock size. In contrast, only two brain structures, the telencephalon and hypothalamus, are correlated with social factors. Telencephalic size is larger in monogamous species compared to polygamous species, as well as with increased numbers of individuals; monogamy is also associated with smaller hypothalamic size. Our results suggest that selection or drift can act independently on different brain regions as the species diverge into different habitats and social systems.

What do bonobos (Pan paniscus) understand about physical contact?

The present study aimed to test what bonobos (Pan paniscus) understand about contact. The task consisted of a clear horizontal tube containing a piece of food and a stick with a disk attached. The bonobos chose which side to push or pull the stick for the disk to contact the food and make it accessible. There were 9 variations in tube design, which differed in the positions of the stick, disk, and food. All 5 bonobos passed at least 1 configuration. A recent study (A. E. Helme, N. S. Clayton, & N. J. Emery, 2006) found that rooks could learn only tube configurations that provided an asymmetrical stick cue, whereas bonobos did not demonstrate an understanding of contact but showed more individual variation, attending to the positions of the food, disk, and stick.

Questioning the social intelligence hypothesis

The social intelligence hypothesis posits that complex cognition and enlarged "executive brains" evolved in response to challenges that are associated with social complexity. This hypothesis has been well supported, but some recent data are inconsistent with its predictions. It is becoming increasingly clear that multiple selective agents, and non-selective constraints, must have acted to shape cognitive abilities in humans and other animals. The task now is to develop a larger theoretical framework that takes into account both inter-specific differences and similarities in cognition. This new framework should facilitate consideration of how selection pressures that are associated with sociality interact with those that are imposed by non-social forms of environmental complexity, and how both types of functional demands interact with phylogenetic and developmental constraints.

How long does it take to become a proficient hunter? Implications for the evolution of extended development and long life span

Human hunting is arguably one of the most difficult activities common to foraging peoples now and in the past. Children and teenagers have usually been described as incompetent hunters in ethnographies of hunter-gatherers. This paper explores the extent to which adult-level competence is limited more by the constraints of physical capital, or body size, and brain-based capital, or skills and learning. The grandmother hypothesis requires that production is an increasing function of size alone, while the embodied capital model stipulates that production is a function of both size and delayed learning. Tests based on observational, interview, and experimental data collected among Tsimane Amerindians of the Bolivian Amazon suggest that size alone cannot explain the long delay until peak hunting productivity. Indirect encounters (e.g., smells, sounds, tracks, and scat) and shooting of stationary targets are two components of hunting ability limited primarily by physical size alone, but the more difficult components of hunting--direct encounters with important prey items and successful capture--require substantial skill. Those skills can take an additional ten to twenty years to develop after achieving adult body size.

Evolution of brain size and juvenile periods in primates

This paper assesses selective pressures that shaped primate life histories, with particular attention to the evolution of longer juvenile periods and increased brain sizes. We evaluate the effects of social complexity (as indexed by group size) and foraging complexity (as indexed by percent fruit and seeds in the diet) on the length of the juvenile period, brain size, and brain ratios (neocortex and executive brain ratios) while controlling for positive covariance among body size, life span, and home range. Results support strong components of diet, life span, and population density acting on juvenile periods and of home range acting on relative brain sizes. Social-complexity arguments for the evolution of primate intelligence are compelling given strong positive correlations between brain ratios and group size while controlling for potential confounding variables. We conclude that both social and ecological components acting at variable intensities in different primate clades are important for understanding variation in primate life histories.