The evolution of intelligence in mammalian carnivores

Adult play and the evolution of tolerant and cooperative societies

Play is generally considered an immature affair. However, adult play is present in several mammal species living in complex social systems. Here, I hypothesize that adult social play is favored by natural selection in those species characterized by high level of social tolerance and/or by the need of others' cooperation to reach a goal (i.e., leverage). The integration and comparison of bio-behavioral data on non-human primates and wild social carnivores allows drawing a comprehensive picture on the importance of adult play in facing unpredictable, novel social situations and in overcoming stressful experiences. The ability to cope with potentially competitive interactions through play can favor the emergence of egalitarian societies. A further interesting and beneficial aspect of adult play is its role in synchronizing group activities and favoring collective decision making by renovating the motivation to cooperate in groupmates. As a last step, some considerations about the presence of adult play in the most egalitarian and cooperative human groups (e.g., hunter-gatherer societies) allows discussing the apparent dichotomy between cultural and biological evolution of certain behavioral traits, including social play in adulthood.

The current state of carnivore cognition

The field of animal cognition has advanced rapidly in the last 25 years. Through careful and creative studies of animals in captivity and in the wild, we have gained critical insights into the evolution of intelligence, the cognitive capacities of a diverse array of taxa, and the importance of ecological and social environments, as well as individual variation, in the expression of cognitive abilities. The field of animal cognition, however, is still being influenced by some historical tendencies. For example, primates and birds are still the majority of study species in the field of animal cognition. Studies of diverse taxa improve the generalizability of our results, are critical for testing evolutionary hypotheses, and open new paths for understanding cognition in species with vastly different morphologies. In this paper, we review the current state of knowledge of cognition in mammalian carnivores. We discuss the advantages of studying cognition in Carnivorans and the immense progress that has been made across many cognitive domains in both lab and field studies of carnivores. We also discuss the current constraints that are associated with studying carnivores. Finally, we explore new directions for future research in studies of carnivore cognition.

The value of individual identification in studies of free-living hyenas and aardwolves

From population estimates to social evolution, much of our understanding of the family Hyaenidae is drawn from studies of known individuals. The extant species in this family (spotted hyenas, Crocuta crocuta, brown hyenas, Parahyaena brunnea, striped hyenas, Hyaena hyaena, and aardwolves, Proteles cristata) are behaviorally diverse, presenting an equally diverse set of logistical constraints on capturing and marking individuals. All these species are individually identifiable by their coat patterns, providing a useful alternative to man-made markings. Many studies have demonstrated the utility of this method in answering a wide range of research questions across all four species, with some employing a creative fusion of techniques. Despite its pervasiveness in basic research on hyenas and aardwolves, individual identification has rarely been applied to the conservation and management of these species. We argue that individual identification using naturally occurring markings in applied research could prove immensely helpful, as this could further improve accuracy of density estimates, reveal characteristics of suitable habitat, identify threats to population persistence, and help to identify individual problem animals.

Learning with lacertids: Studying the link between ecology and cognition within a comparative framework

Cognition is an essential tool for animals to deal with environmental challenges. Nonetheless, the ecological forces driving the evolution of cognition throughout the animal kingdom remain enigmatic. Large-scale comparative studies on multiple species and cognitive traits have been advanced as the best way to facilitate our understanding of cognitive evolution, but such studies are rare. Here, we tested 13 species of lacertid lizards (Reptilia: Lacertidae) using a battery of cognitive tests measuring inhibitory control, problem-solving, and spatial and reversal learning. Next, we tested the relationship between species' performance and (a) resource availability (temperature and precipitation), habitat complexity (Normalized Difference Vegetation Index), and habitat variability (seasonality) in their natural habitat and (b) their life history (size at hatching and maturity, clutch size, and frequency). Although species differed markedly in their cognitive abilities, such variation was mostly unrelated to their ecology and life history. Yet, species living in more variable environments exhibited lower behavioral flexibility, likely due to energetic constrains in such habitats. Our standardized protocols provide opportunities for collaborative research, allowing increased sample sizes and replication, essential for moving forward in the field of comparative cognition. Follow-up studies could include more detailed measures of habitat structure and look at other potential selective drivers such as predation.

The impact of environmental factors on the evolution of brain size in carnivorans

The reasons why some animals have developed larger brains has long been a subject of debate. Yet, it remains unclear which selective pressures may favour the encephalization and how it may act during evolution at different taxonomic scales. Here we studied the patterns and tempo of brain evolution within the order Carnivora and present large-scale comparative analysis of the effect of ecological, environmental, social, and physiological variables on relative brain size in a sample of 174 extant carnivoran species. We found a complex pattern of brain size change between carnivoran families with differences in both the rate and diversity of encephalization. Our findings suggest that during carnivorans’ evolution, a trade-off have occurred between the cognitive advantages of acquiring a relatively large brain allowing to adapt to specific environments, and the metabolic costs of the brain which may constitute a disadvantage when facing the need to colonize new environments.

The brain size of carnivores has evolved to balance a trade-off between increased cognitive function and increased metabolic cost.

The impact of environmental factors on the evolution of brain size in carnivorans

The reasons why some animals have developed larger brains has long been a subject of debate. Yet, it remains unclear which selective pressures may favour the encephalization and how it may act during evolution at different taxonomic scales. Here we studied the patterns and tempo of brain evolution within the order Carnivora and present large-scale comparative analysis of the effect of ecological, environmental, social, and physiological variables on relative brain size in a sample of 174 extant carnivoran species. We found a complex pattern of brain size change between carnivoran families with differences in both the rate and diversity of encephalization. Our findings suggest that during carnivorans' evolution, a trade-off have occurred between the cognitive advantages of acquiring a relatively large brain allowing to adapt to specific environments, and the metabolic costs of the brain which may constitute a disadvantage when facing the need to colonize new environments.

Down a Rabbit Hole: Burrowing Behaviour and Larger Home Ranges are Related to Larger Brains in Leporids

Studies on the evolution of brain size variation usually focus on large clades encompassing broad phylogenetic groups. This risks introducing ‘noise’ in the results, often obscuring effects that might be detected in less inclusive clades. Here, we focus on a sample of endocranial volumes (endocasts) of 18 species of rabbits and hares (Lagomorpha: Leporidae), which are a discrete radiation of mammals with a suitably large range of body sizes. Using 60 individuals, we test five popular hypotheses on brain size and olfactory bulb evolution in mammals. We also address the pervasive issue of missing data, using multiple phylogenetic imputations as to conserve the full sample size for all analyses. Our analyses show that home range and burrowing behaviour are the only predictors of leporid brain size variation. Litter size, which is one of the most widely reported constraints on brain size, was unexpectedly not associated with brain size. However, a constraining effect may be masked by a strong association of litter size with temperature seasonality, warranting further study. Lastly, we show that unreasonable estimations of phylogenetic signal (Pagel’s lamba) warrant additional caution when using small sample sizes, such as ours, in comparative studies.

Relative Brain Volume of Carnivorans Has Evolved in Correlation with Environmental and Dietary Variables Differentially among Clades

Carnivorans possess relatively large brains compared to most other mammalian clades. Factors like environmental complexity (Cognitive Buffer Hypothesis) and diet quality (Expensive-Tissue Hypothesis) have been proposed as mechanisms for encephalization in other large-brained clades. We examine whether the Cognitive Buffer and Expensive-Tissue Hypotheses account for brain size variation within Carnivora. Under these hypotheses, we predict a positive correlation between brain size and environmental complexity or protein consumption. Relative endocranial volume (phylogenetic generalized least-squares residual from species' mean body mass) and 9 environmental and dietary variables were collected from the literature for 148 species of terrestrial and marine carnivorans. We found that the correlation between relative brain volume and environment and diet differed among clades, a trend consistent with other larger brained vertebrates (i.e., Primates, Aves). Mustelidae and Procyonidae demonstrate larger brains in species with higher-quality diets, consistent with the Expensive-Tissue Hypothesis, while in Herpestidae, correlations between relative brain size and environment are consistent with the Cognitive Buffer Hypothesis. Our results indicate that carnivorans may have evolved relatively larger brains under similar selective pressures as primates despite the considerable differences in life history and behavior between these two clades.

Large and expensive brain comes with a short lifespan: The relationship between brain size and longevity among fish taxa

Vertebrates show substantial interspecific variation in brain size in relation to body mass. It has long been recognized that the evolution of large brains is associated with both costs and benefits, and it is their net benefit which should be favoured by natural selection. On one hand, the substantial energetic cost imposed by the maintenance of neural tissue is expected to compromise the energetic budget of organisms with large brains and their investment in other critical organs (expensive brain framework, EBF) or important physiological process, such as somatic maintenance and repair, thus accelerating ageing that shortens lifespan, as predicted by the disposable soma theory (DST). However, selection towards larger brain size can provide cognitive benefits (e.g., high behavioural flexibility) that may mitigate extrinsic mortality pressures, and thus may indirectly select for slower ageing that prolongs lifespan, as predicted by the cognitive buffer hypothesis (CBH). The relationship between longevity and brain size has been investigated to date only among terrestrial vertebrates, although the same selective forces acting on those species may also affect vertebrates living in aquatic habitats, such as fish. Thus, whether this evolutionary trade-off for brain size and longevity exists on a large scale among fish clades remains to be addressed. In this study, using a global dataset of 407 fish species, I undertook the first phylogenetic test of the brain size/longevity relationship in aquatic vertebrate species. The study revealed a negative relationship between brain size and longevity among cartilaginous fish confirming EBF and DST. However, no pattern emerged among bony fish species. Among sharks and rays, the high metabolic cost of producing neural tissue transcends the cognitive benefits of evolving a larger brain. Consequently, my findings suggest that the cost of maintaining brain tissue is relatively higher in ectothermic species than in endothermic ones.

Why big brains? A comparison of models for both primate and carnivore brain size evolution

Despite decades of research, much uncertainty remains regarding the selection pressures responsible for brain size variation. Whilst the influential social brain hypothesis once garnered extensive support, more recent studies have failed to find support for a link between brain size and sociality. Instead, it appears there is now substantial evidence suggesting ecology better predicts brain size in both primates and carnivores. Here, different models of brain evolution were tested, and the relative importance of social, ecological, and life-history traits were assessed on both overall encephalisation and specific brain regions. In primates, evidence is found for consistent associations between brain size and ecological factors, particularly diet; however, evidence was also found advocating sociality as a selection pressure driving brain size. In carnivores, evidence suggests ecological variables, most notably home range size, are influencing brain size; whereas, no support is found for the social brain hypothesis, perhaps reflecting the fact sociality appears to be limited to a select few taxa. Life-history associations reveal complex selection mechanisms to be counterbalancing the costs associated with expensive brain tissue through extended developmental periods, reduced fertility, and extended maximum lifespan. Future studies should give careful consideration of the methods chosen for measuring brain size, investigate both whole brain and specific brain regions where possible, and look to integrate multiple variables, thus fully capturing all of the potential factors influencing brain size.

Mate Choice, Sex Roles and Sexual Cognition: Neuronal Prerequisites Supporting Cognitive Mate Choice

Across taxa, mate choice is a highly selective process involving both intra- and intersexual selection processes aiming to pass on one’s genes, making mate choice a pivotal tool of sexual selection. Individuals adapt mate choice behavior dynamically in response to environmental and social changes. These changes are perceived sensorily and integrated on a neuronal level, which ultimately leads to an adequate behavioral response. Along with perception and prior to an appropriate behavioral response, the choosing sex has (1) to recognize and discriminate between the prospective mates and (2) to be able to assess and compare their performance in order to make an informed decision. To do so, cognitive processes allow for the simultaneous processing of multiple information from the (in-) animate environment as well as from a variety of both sexual and social (but non-sexual) conspecific cues. Although many behavioral aspects of cognition on one side and of mate choice displays on the other are well understood, the interplay of neuronal mechanisms governing both determinants, i.e., governing cognitive mate choice have been described only vaguely. This review aimed to throw a spotlight on neuronal prerequisites, networks and processes supporting the interaction between mate choice, sex roles and sexual cognition, hence, supporting cognitive mate choice. How does neuronal activity differ between males and females regarding social cognition? Does sex or the respective sex role within the prevailing mating system mirror at a neuronal level? How does cognitive competence affect mate choice? Conversely, how does mate choice affect the cognitive abilities of both sexes? Benefitting from studies using different neuroanatomical techniques such as neuronal activity markers, differential coexpression or candidate gene analyses, modulatory effects of neurotransmitters and hormones, or imaging techniques such as fMRI, there is ample evidence pointing to a reflection of sex and the respective sex role at the neuronal level, at least in individual brain regions. Moreover, this review aims to summarize evidence for cognitive abilities influencing mate choice and vice versa. At the same time, new questions arise centering the complex relationship between neurobiology, cognition and mate choice, which we will perhaps be able to answer with new experimental techniques.

Testing hypotheses of marsupial brain size variation using phylogenetic multiple imputations and a Bayesian comparative framework

Considerable controversy exists about which hypotheses and variables best explain mammalian brain size variation. We use a new, high-coverage dataset of marsupial brain and body sizes, and the first phylogenetically imputed full datasets of 16 predictor variables, to model the prevalent hypotheses explaining brain size evolution using phylogenetically corrected Bayesian generalized linear mixed-effects modelling. Despite this comprehensive analysis, litter size emerges as the only significant predictor. Marsupials differ from the more frequently studied placentals in displaying a much lower diversity of reproductive traits, which are known to interact extensively with many behavioural and ecological predictors of brain size. Our results therefore suggest that studies of relative brain size evolution in placental mammals may require targeted co-analysis or adjustment of reproductive parameters like litter size, weaning age or gestation length. This supports suggestions that significant associations between behavioural or ecological variables with relative brain size may be due to a confounding influence of the extensive reproductive diversity of placental mammals.

Animal Creativity as a Function of Behavioral Innovation and Behavior Flexibility in Problem-solving Situations

A natural approach of animal creativity through insightful problem-solving may offer a panel of how physiological, contextual, cultural and developmental variables related to each other to produce new behaviors. The spontaneous interconnection of acquire behaviors is an Insightful Problem-Solving model based on the new combination and/or chaining of behaviors that were previously and independently trained. This model seems to offer an integrative alternative for the studies of Innovation and Behavioral Flexibility because it allows the research on innovation in a scenario in which the response that solves the problem situation is not available by trial-and-error. Measuring task-appropriateness by behavior flexibility and novelty by behavior innovation under insightful problem-solving paradigm can contribute for the integration of decades of evidence in Cognitive Psychology, Neuro-ethology, Behavior Analysis and Behavioral Neurosciences. The Insightful Problem-Solving allows the independent test of behavioral innovation and behavioral flexibility as it measures the behavioral innovation inside insightful test and tests if the BF depends on variables arranged in the problem-situation and/or on the previous training (e.g. familiarity with access to appetitive stimulus in the pre-test, the number of distinct behaviors trained, and contingency changes in the post-test).

Variation in reversal learning by three generalist mesocarnivores

Urbanization imposes novel challenges for wildlife, but also provides new opportunities for exploitation. Generalist species are commonly found in urban habitats, but the cognitive mechanisms facilitating their successful behavioral adaptations and exploitations are largely under-investigated. Cognitive flexibility is thought to enable generalists to be more plastic in their behavior, thereby increasing their adaptability to a variety of environments, including urban habitats. Yet direct measures of cognitive flexibility across urban wildlife are lacking. We used a classic reversal-learning paradigm to investigate the cognitive flexibility of three generalist mesocarnivores commonly found in urban habitats: striped skunks (Mephitis mephitis), raccoons (Procyon lotor), and coyotes (Canis latrans). We developed an automated device and testing protocol that allowed us to administer tests of reversal learning in captivity without extensive training or experimenter involvement. Although most subjects were able to rapidly form and reverse learned associations, we found moderate variation in performance and behavior during trials. Most notably, we observed heightened neophobia and a lack of habituation expressed by coyotes. We discuss the implications of such differences among generalists with regard to urban adaptation and we identify goals for future research. This study is an important step in investigating the relationships between cognition, generalism, and urban adaptation.

Validity of Cognitive Tests for Non-human Animals: Pitfalls and Prospects

Comparative psychology assesses cognitive abilities and capacities of non-human animals and humans. Based on performance differences and similarities in various species in cognitive tests, it is inferred how their minds work and reconstructed how cognition might have evolved. Critically, such species comparisons are only valid and meaningful if the tasks truly capture individual and inter-specific variation in cognitive abilities rather than contextual variables that might affect task performance. Unlike in human test psychology, however, cognitive tasks for non-human primates (and most other animals) have been rarely evaluated regarding their measurement validity. We review recent studies that address how non-cognitive factors affect performance in a set of commonly used cognitive tasks, and if cognitive tests truly measure individual variation in cognitive abilities. We find that individual differences in emotional and motivational factors primarily affect performance via attention. Hence, it is crucial to systematically control for attention during cognitive tasks to obtain valid and reliable results. Aspects of test design, however, can also have a substantial effect on cognitive performance. We conclude that non-cognitive factors are a minor source of measurement error if acknowledged and properly controlled for. It is essential, however, to validate and eventually re-design several primate cognition tasks in order to ascertain that they capture the cognitive abilities they were designed to measure. This will provide a more solid base for future cognitive comparisons within primates but also across a wider range of non-human animal species.

The face of animal cognition

As an increasing number of researchers investigate the cognitive abilities of an ever-wider range of animals, animal cognition is currently among the most exciting fields within animal behavior. Tinbergen would be proud: all four of his approaches are being pursued and we are learning much about how animals collect information and how they use that information to make decisions for their current and future states as well as what animals do not perceive or choose to ignore. Here I provide an overview of this productivity, alighting only briefly on any single example, to showcase the diversity of species, of approaches and the sheer mass of research effort currently under way. We are getting closer to understanding the minds of other animals and the evolution of cognition at an increasingly rapid rate.

An evolutionary perspective on paranoia

Paranoia is the most common symptom of psychosis but paranoid concerns occur throughout the general population. Here, we argue for an evolutionary approach to paranoia across the spectrum of severity that accounts for its complex social phenomenology - including the perception of conspiracy and selective identification of perceived persecutors - and considers how it can be understood in light of our evolved social cognition. We argue that the presence of coalitions and coordination between groups in competitive situations could favour psychological mechanisms that detect, anticipate and avoid social threats. Our hypothesis makes testable predictions about the environments in which paranoia should be most common as well as the developmental trajectory of paranoia across the lifespan. We suggest that paranoia should not solely be viewed as a pathological symptom of a mental disorder but also as a part of a normally-functioning human psychology.

The Cultural Brain Hypothesis: How culture drives brain expansion, sociality, and life history

In the last few million years, the hominin brain more than tripled in size. Comparisons across evolutionary lineages suggest that this expansion may be part of a broader trend toward larger, more complex brains in many taxa. Efforts to understand the evolutionary forces driving brain expansion have focused on climatic, ecological, and social factors. Here, building on existing research on learning, we analytically and computationally model the predictions of two closely related hypotheses: The Cultural Brain Hypothesis and the Cumulative Cultural Brain Hypothesis. The Cultural Brain Hypothesis posits that brains have been selected for their ability to store and manage information, acquired through asocial or social learning. The model of the Cultural Brain Hypothesis reveals relationships between brain size, group size, innovation, social learning, mating structures, and the length of the juvenile period that are supported by the existing empirical literature. From this model, we derive a set of predictions-the Cumulative Cultural Brain Hypothesis-for the conditions that favor an autocatalytic take-off characteristic of human evolution. This narrow evolutionary pathway, created by cumulative cultural evolution, may help explain the rapid expansion of human brains and other aspects of our species' life history and psychology.

Individual differences: Case studies of rodent and primate intelligence

Early in the 20th century, individual differences were a central focus of psychologists. By the end of that century, studies of individual differences had become far less common, and attention to these differences played little role in the development of contemporary theory. To illustrate the important role of individual differences, here we consider variations in intelligence as a compelling example. General intelligence (g) has now been demonstrated in at least 2 distinct genera: primates (including humans, chimpanzees, bonobos, and tamarins) and rodents (mice and rats). The expression of general intelligence varies widely across individuals within a species; these variations have tremendous functional consequence, and are attributable to interactions of genes and environment. Here we provide evidence for these assertions, describe the processes that contribute to variations in general intelligence, as well as the methods that underlie the analysis of individual differences. We conclude by describing why consideration of individual differences is critical to our understanding of learning, cognition, and behavior, and illustrate how attention to individual differences can contribute to more effective administration of therapeutic strategies for psychological disorders. (PsycINFO Database Record