Problems with comparative analyses of avian brain size

There are multiple hypotheses for the evolution of cognition. The most prominent hypotheses are the Social Intelligence Hypothesis (SIH) and the Ecological Intelligence Hypothesis (EIH), which are often pitted against one another. These hypotheses tend to be tested using broad-scale comparative studies of brain size, where brain size is used as a proxy of cognitive ability, and various social and/or ecological variables are included as predictors. Here, we test how methodologically robust such analyses are. First, we investigate variation in brain and body size measurements across >1000 species of bird. We demonstrate that there is substantial variation in brain and body size estimates across datasets, indicating that conclusions drawn from comparative brain size models are likely to differ depending on the source of the data. Following this, we subset our data to the Corvides infraorder and interrogate how modelling decisions impact results. We show that model results change substantially depending on variable inclusion, source and classification. Indeed, we could have drawn multiple contradictory conclusions about the principal drivers of brain size evolution. These results reflect recent concerns that current methods in comparative brain size studies are not robust. We add our voices to a growing community of researchers suggesting that we move on from using such methods to investigate cognitive evolution. We suggest that a more fruitful way forward is to instead use direct measures of cognitive performance to interrogate why variation in cognition arises within species and between closely related taxa.

A tehetség eredete

Tanulmányunkban a tehetség két aspektusát elemezzük. Az egyik szinten arra a kérdésre keresünk választ, hogy milyen örökletes tényezők tehetők felelőssé a lángész kialakulásáért. Megállapítjuk, hogy a jelenlegi kutatások szerint a tehetség mögött nem fedezhetők fel specifikus gének, de lehetségesek olyan genetikai hatások, amelyek egyfajta emergens szerveződése teremti meg az alapját a lángész kialakulásának – természetesen a különböző környezeti hatásokkal kölcsönhatásban. A másik szintű elemzésben a tehetség evolúciós eredetére kérdezünk rá, és négy olyan humánspecifikus kognitív képesség kialakulását elemezzük, amelyek fontos szerepet játszhatnak a szellemi kiválóság megjelenésében. Nevezetesen arra teszünk kísérletet, hogy megértsük az elmeolvasás, rugalmas gondolkodás, nyelv és kreativitás evolúciós létrejöttét. Ehhez olyan magyarázó model-leket veszünk igénybe, mint a Szociális Intelligencia, Machiavelli Intelligencia, Szexuális Szelekció és Fluid Intelligencia hipotézisek. E magyarázatok megerősítése további kutatásokat igényel.In this paper, two aspects of talent are analyzed. On the one level, I am looking for an answer to what hereditary factors would be responsible for the development of talent. In the light of the current studies, no specific genes have been found to prescribe talent. However, possible genetic effects with an emergent property of their mutual relationships may create the basis of formation of genius – obviously interacting with the environmental effects. On the other level of analysis I am focusing on the evolutionary background of talent. Four human specific cognitive abilities are analyzed that play important roles in the formation of intellectual excellence: mind reading, flexible thought, language, and creativity. The explanations to the evolution of these abilities include Social Intelligence Hypothesis, Machiavellian Intelligence Hypothesis, Sexual Selection Theory, and Fluid Intelligence Hypothesis. The confirmation of these explanations requires further studies.

The Social Brain

The first discussion of a relationship between sociality and intelligence came in the middle of the twentieth century, especially by Humphrey who suggested that living socially demanded intellectual abilities above and beyond those required by an animal’s ecology. This led to the Social Intelligence Hypothesis, and then the Machiavellian Intelligence Hypothesis, both proposing that sociality was the main driver of the superior intellect of primates, especially humans. Two key challenges for this hypothesis are that sociality is difficult to quantify and cognition is not well tested by problem solving. More importantly, as data from more species have been examined, the analyses increasingly fail to show that sociality explains variation in brain size, even in primates. I conclude that appealing as this hypothesis is, it does not do a very compelling job of explaining variation in brain size.

Interactions with conspecific outsiders as drivers of cognitive evolution

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.

Social Intelligence and Altruism

According to the social intelligence hypothesis, the unusual enlargement of primate brains, including the human brain, was driven by the complexity of social decision-making primates face in their societies. Social decision-making is fundamentally more complex due to the recursive nature of social reasoning. This chapter begins with the review of game theory and illustrates how game theory has transformed neuroscience research on social decision-making. Some of the topics covered include the supposed death of game theory, altruism and its dark side, cooperation, the theory of the mind, the prisoner’s dilemma, the recursive mind, and the social brain.

An intraspecific appraisal of the social intelligence hypothesis

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’.

Wild acorn woodpeckers recognize associations between individuals in other groups

According to the social intelligence hypothesis, understanding the cognitive demands of the social environment is key to understanding the evolution of intelligence. Many important socio-cognitive abilities, however, have primarily been studied in a narrow subset of the social environment—within-group social interactions—despite the fact that between-group social interactions often have a substantial effect on fitness. In particular, triadic awareness (knowledge about the relationships and associations between others) is critical for navigating many types of complex social interactions, yet no existing study has investigated whether wild animals can track associations between members of other social groups. We investigated inter-group triadic awareness in wild acorn woodpeckers ( Melanerpes formicivorus ), a socially complex group-living bird. We presented woodpeckers with socially incongruous playbacks that simulated two outsiders from different groups calling together, and socially congruous playbacks that simulated two outsiders from the same group calling together. Subjects responded more quickly to the incongruous playbacks, suggesting that they were aware that the callers belonged to two different groups. This study provides the first demonstration that animals can recognize associations between members of other groups under natural circumstances, and highlights the importance of considering how inter-group social selection pressures may influence the evolution of cognition.

The evolution of intelligence in mammalian carnivores

Although intelligence should theoretically evolve to help animals solve specific types of problems posed by the environment, it is unclear which environmental challenges favour enhanced cognition, or how general intelligence evolves along with domain-specific cognitive abilities. The social intelligence hypothesis posits that big brains and great intelligence have evolved to cope with the labile behaviour of group mates. We have exploited the remarkable convergence in social complexity between cercopithecine primates and spotted hyaenas to test predictions of the social intelligence hypothesis in regard to both cognition and brain size. Behavioural data indicate that there has been considerable convergence between primates and hyaenas with respect to their social cognitive abilities. Moreover, compared with other hyaena species, spotted hyaenas have larger brains and expanded frontal cortex, as predicted by the social intelligence hypothesis. However, broader comparative study suggests that domain-general intelligence in carnivores probably did not evolve in response to selection pressures imposed specifically in the social domain. The cognitive buffer hypothesis, which suggests that general intelligence evolves to help animals cope with novel or changing environments, appears to offer a more robust explanation for general intelligence in carnivores than any hypothesis invoking selection pressures imposed strictly by sociality or foraging demands.