The Social Intelligence Hypothesis argues that the demands of social life drive cognitive evolution1–3. This idea receives support from comparative studies linking variation in group size or mating systems with cognitive and neuroanatomical differences across species3–7, but findings are contradictory and contentious8–10. To understand the cognitive consequences of sociality it is also important to investigate social variation within species. Here we show that in wild, cooperatively breeding Australian magpies, individuals living in larger groups show elevated cognitive performance, which in turn is linked to increased reproductive success. Individual performance was highly correlated across four cognitive tasks, hinting towards a “general intelligence factor” underlying cognitive performance. Repeated cognitive testing of juveniles at different ages showed that the group size – cognition correlation emerged in early life, suggesting that living in larger groups promotes cognitive development. Furthermore, we found a positive association between female task performance and three indicators of reproductive success, thus identifying a selective benefit of greater cognitive performance. Together, these results provide critical intraspecific evidence that sociality can shape cognitive development and evolution.

The prevailing hypotheses for the evolution of cognition focus on either the demands associated with group living (the social intelligence hypothesis (SIH)) or ecological challenges such as finding food. Comparative studies testing these hypotheses have generated highly conflicting results; consequently, our understanding of the drivers of cognitive evolution remains limited. To understand how selection shapes cognition, research must incorporate an intraspecific approach, focusing on the causes and consequences of individual variation in cognition. Here, we review the findings of recent intraspecific cognitive research to investigate the predictions of the SIH. Extensive evidence from our own research on Australian magpies (Cracticus tibicen dorsalis), and a number of other taxa, suggests that individuals in larger social groups exhibit elevated cognitive performance and, in some cases, elevated reproductive fitness. Not only do these findings demonstrate how the social environment has the potential to shape cognitive evolution, but crucially, they demonstrate the importance of considering both genetic and developmental factors when attempting to explain the causes of cognitive variation.This article is part of the theme issue ‘Causes and consequences of individual differences in cognitive abilities’.

The social intelligence hypothesis (SIH) posits that within-group interactions drive cognitive evolution, but it has received equivocal support. We argue the SIH overlooks a major component of social life: interactions with conspecific outsiders. Competition for vital resources means conspecific outsiders present myriad threats and opportunities in all animal taxa across the social spectrum (from individuals to groups). We detail cognitive challenges generated by conspecific outsiders, arguing these select for ‘Napoleonic’ intelligence; explain potential influences on the SIH; and highlight important considerations when empirically testing these ideas. Including interactions with conspecific outsiders may substantially improve our understanding of cognitive evolution.

In cooperatively breeding species, the level of investment in young can vary substantially. Despite receiving considerable research attention, how and why investment in young varies with cooperatively breeding group members remains unclear. To investigate the causes of variation in care of young, we assessed patterns of both helper and parental behavior in the cooperatively breeding Western Australian magpie (Cracticus tibicen dorsalis). Observations of 19 helpers and 31 parents provisioning 33 broods raised in 11 different groups over two consecutive breeding seasons revealed substantial variation in offspring care behavior. Our results suggest that the level of investment in young by helpers is strongly influenced by group size, chick age, and individual helper traits (including foraging efficiency, age and sex). Helping behavior was facultative, and individuals from smaller groups were more likely to invest in helping behavior. Overall, the number of broods receiving help was lowest during the nestling phase and highest during the fledgling phase. Female helpers provided more care than both male and juvenile helpers. We found that mothers invest more time in offspring care than do fathers, however fathers increase their effort in the presence of helpers while mothers do not. Overall, helper care was additive to parental care and therefore helping behavior may be beneficial to the brood. Our research reveals that variation in offspring care in magpies is influenced by both social and individual traits.

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The benefits of group living have traditionally been attributed to risk dilution or the efficient exploitation of resources; individuals in social groups may therefore benefit from access to valuable information. If sociality facilitates access to information, then individuals in larger groups may be predicted to solve novel problems faster than individuals in smaller groups. Additionally, larger group sizes may facilitate the subsequent spread of innovations within animal groups, as has been proposed for human societies. We presented a novel foraging task (where a food reward could be accessed by pushing a self-shutting sliding door) to 16 groups of wild, cooperatively breeding Australian magpies, Cracticus tibicen dorsalis, ranging in size from two to 11 individuals. We found a nonlinear decline in the time taken for the innovative behaviour to emerge with increasing group size, and social information use facilitated the transmission of novel behaviour, with it spreading more quickly in larger than smaller groups. This study provides important evidence for a nonlinear relationship between group size and the emergence of innovation (and its subsequent transmission) in a wild population of animals. Further work investigating the scope and strength of group size–innovation relationships, and the mechanisms underpinning them, will help us understand the potential advantages of living in larger social groups.

With global surface air temperature rising rapidly, extensive research effort has been dedicated to assessing the consequences of this change for wildlife. While impacts on the phenology, distribution, and demography of wild animal populations are well documented, the impact of increasing temperature on cognition in these populations has received relatively little attention. Cognition encompasses the mental mechanisms that allow individuals to process information from the surrounding environment, respond accordingly, and flexibly adjust behavior. Hence, it is likely to be a key factor in allowing animals to adjust adaptively to climate change. Captive studies show that heat stress can negatively affect cognitive performance not only in the short‐term but also in the long‐term, by altering cognitive development at early life stages. Field studies indicate that cognitive performance may affect survival and reproductive success. However, the link between heat stress, cognition, and fitness in wild animals has yet to be formally established. We propose a comprehensive research framework for the collection of robust empirical datasets on heat stress and cognitive performance in the wild. We then suggest how knowledge of heat stress impacts on cognitive performance could be applied to population viability models and wildlife management actions. We believe that a joint research effort encompassing the fields of thermal physiology, behavioral ecology, comparative cognition, and conservation science, is essential to provide timely mitigation measures against the potential impacts of climate change on wildlife. This article is categorized under: Climate, Ecology, and Conservation > Observed Ecological Changes

Identifying the causes and fitness consequences of intraspecific variation in cognitive performance is fundamental to understand how cognition evolves. Selection may act on different cognitive traits separately or jointly as part of the general cognitive performance (GCP) of the individual. To date, few studies have examined simultaneously whether individual cognitive performance covaries across different cognitive tasks, the relative importance of individual and social attributes in determining cognitive variation, and its fitness consequences in the wild. Here, we tested 38 wild southern pied babblers ( Turdoides bicolor ) on a cognitive test battery targeting associative learning, reversal learning and inhibitory control. We found that a single factor explained 59.5% of the variation in individual cognitive performance across tasks, suggestive of a general cognitive factor. GCP varied by age and sex; declining with age in females but not males. Older females also tended to produce a higher average number of fledglings per year compared to younger females. Analysing over 10 years of breeding data, we found that individuals with lower general cognitive performance produced more fledglings per year. Collectively, our findings support the existence of a trade-off between cognitive performance and reproductive success in a wild bird.