Cognition presents evolutionary research with one of its greatest challenges. Cognitive evolution has been explained at the proximate level by shifts in absolute and relative brain volume and at the ultimate level by differences in social and dietary complexity. However, no study has integrated the experimental and phylogenetic approach at the scale required to rigorously test these explanations. Instead, previous research has largely relied on various measures of brain size as proxies for cognitive abilities. We experimentally evaluated these major evolutionary explanations by quantitatively comparing the cognitive performance of 567 individuals representing 36 species on two problem-solving tasks measuring self-control. Phylogenetic analysis revealed that absolute brain volume best predicted performance across species and accounted for considerably more variance than brain volume controlling for body mass. This result corroborates recent advances in evolutionary neurobiology and illustrates the cognitive consequences of cortical reorganization through increases in brain volume. Within primates, dietary breadth but not social group size was a strong predictor of species differences in self-control. Our results implicate robust evolutionary relationships between dietary breadth, absolute brain volume, and self-control. These findings provide a significant first step toward quantifying the primate cognitive phenome and explaining the process of cognitive evolution.psychology | behavior | comparative methods | inhibitory control | executive function S ince Darwin, understanding the evolution of cognition has been widely regarded as one of the greatest challenges for evolutionary research (1). Although researchers have identified surprising cognitive flexibility in a range of species (2-40) and potentially derived features of human psychology (41-61), we know much less about the major forces shaping cognitive evolution (62-71). With the notable exception of Bitterman's landmark studies conducted several decades ago (63, 72-74), most research comparing cognition across species has been limited to small taxonomic samples (70, 75). With limited comparable experimental data on how cognition varies across species, previous research has largely relied on proxies for cognition (e.g., brain size) or metaanalyses when testing hypotheses about cognitive evolution (76-92). The lack of cognitive data collected with similar methods across large samples of species precludes meaningful species comparisons that can reveal the major forces shaping cognitive evolution across species, including humans (48,70,89,(93)(94)(95)(96)(97)(98). SignificanceAlthough scientists have identified surprising cognitive flexibility in animals and potentially unique features of human psychology, we know less about the selective forces that favor cognitive evolution, or the proximate biological mechanisms underlying this process. We tested 36 species in two problemsolving tasks measuring self-control and evaluated the leading hypotheses regarding how ...

Keywords: cognitive test battery g general intelligence factor individual variation Petroica longipesIn human psychometric testing, individuals' scores in tests of diverse cognitive processes are positively correlated, with a 'general intelligence' factor (g) typically accounting for at least 40% of total variance. Individual differences in cognitive ability have been extensively studied in humans, yet they have received far less attention in nonhuman animals. In particular, the development of a test battery suitable for quantifying individual cognitive performance in birds remains in its infancy. Additionally, implementing this approach in the wild, where the ecological significance of cognition can also be explored, presents considerable logistical challenges for most species. We developed a cognitive test battery for wild New Zealand North Island robins. Our battery comprised six tasks based on established measures of avian cognitive performance: a motor task, colour and shape discrimination, reversal learning, spatial memory and inhibitory control. Robins varied greatly in their ability to solve these tasks and we found weakly positive, nonsignificant correlations between most tasks. A principal components analysis of task performances yielded two factors with eigenvalues >1. The first component extracted explained over 34% of the variance in cognitive performance and all six tasks loaded positively on this first component. We show, using randomization tests, that these results are robust. Our results thus suggest that a general cognitive factor, analogous to human g, underpins cognitive performance in wild North Island robins tested in their natural habitat.

State-attribution is the ability to ascribe to others an internal life like one's own and to understand that internal, psychological states such as desire, hope, belief, and knowledge underlie others' actions. Despite extensive research, comparative studies struggle to adequately integrate key factors of state-attribution that have been identified by evolutionary and developmental psychology as well as research on empathy. Here, we develop a behavioral paradigm to address these issues and investigate whether male Eurasian jays respond to the changing desire-state of their female partners when sharing food. We demonstrate that males feed their mates flexibly according to the female's current food preference. Critically, we show that the males need to see what the female has previously eaten to know what food she will currently want. Consequently, the males' sharing pattern was not simply a response to their mate's behavior indicating her preference as to what he should share, nor was it a response to the males' own desire-state. Our results raise the possibility that these birds may be capable of ascribing desire to their mates.corvid | Theory of Mind | cooperation | specific satiety I n human development, the earliest manifestation of state-attribution is the ability to explain and predict others' behavior in terms of desire-states (e.g., wants, wishes, hopes), a capacity that does not require a concept of others' mental representations (1, 2). At around the age of four, the more complex desire-belief system is formed by incorporating the attribution of epistemic mental states (e.g., belief, knowledge, doubt, expectation) (3, 4), an ability known as Theory of Mind. It is very possible that the attribution of desire-states may represent not only the developmental, but also the evolutionary, precursor of Theory of Mind. Thus, the first logical step in the investigation of state-attribution in nonhuman animals should be to search for this simpler manifestation (5). Despite this, most comparative studies focus solely on the attribution of epistemic mental states (6-13).A notable exception claims that apes can retrospectively infer humans' desires toward food items from the emotions expressed (14). However, given that the apes were explicitly trained about the relationship between human expressions and the availability of food, we cannot conclude that the apes inferred an underlying desire. In another study, the authors claimed that capuchin monkeys (Cebus apella) attribute a need or desire to another individual and thus might exhibit empathetic perspective-taking because the number of tolerated thefts by another individual was lower after subjects had seen the other individual eat than when they had not (15). Unfortunately, this study failed to account for a much simpler competitive account, namely that the sight of another monkey eating triggered the monkeys to protect their food. A second issue is that this experimental paradigm could only investigate the understanding of another individual's physiological process...

For the past two decades, behavioural ecologists have documented consistent individual differences in behavioural traits within species and found evidence for animal "personality". It is only relatively recently, however, that increasing numbers of researchers have begun to investigate individual differences in cognitive ability within species. It has been suggested that cognitive test batteries may provide an ideal tool for this growing research endeavour. In fact, cognitive test batteries have now been used to examine the causes, consequences and underlying structure of cognitive performance within and between many species. In this review, we document the existing attempts to develop cognitive test batteries for non-human animals and review the claims that these studies have made in terms of the structure and evolution of cognition. We argue that our current test battery methods could be improved on multiple fronts, from the design of tasks, to the domains targeted and the species tested. Refining and optimising test battery design will provide many benefits. In future, we envisage that well-designed cognitive test batteries may provide answers to a range of exciting questions, including giving us greater insight into the evolution and structure of cognition.

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Humans' predictions of another person's behaviour are regularly influenced by what they themselves might know or want. In a previous study, we found that male Eurasian jays (Garrulus glandarius) could cater for their female partner's current desire when sharing food with her. Here, we tested the extent to which the males' decisions are influenced by their own current desire. When the males' and female's desires matched, males correctly shared the food that was desired by both. When the female's desire differed from their own, the males' decisions were not entirely driven by their own desires, suggesting that males also took the female's desire into account. Thus, the male jays' decisions about their mates' desires are partially biased by their own desire and might be based upon similar processes as those found in humans.

Highlights d The link between reproduction and spatial memory is unexplored in caching species d Memory performance influenced male robin (Petroica longipes) reproductive success d Superior male memory performance was associated with efficient offspring provisioning d Sex differences in these links may act to maintain cognitive variation in the wild