The evolutionary puzzle of cognition: challenges and insights from individual-based studies

Abstract

Cognition is widely believed to confer adaptive benefits, yet empirically demonstrating these benefits and understanding their evolutionary origin remains a significant challenge. Individual-based studies in the wild are essential for demonstrating that a cognitive trait is an adaptation. However, such approaches have so far yielded only partial evidence for the adaptive significance of cognition. Building on previous research, we highlight key challenges of individual-based studies that remain underappreciated and warrant further attention. These include the need for precise characterization of functionally relevant cognitive traits, a deeper understanding of heritable variation, more robust assessments of key fitness components across large cohorts and extended timescales, and clearer identification of the fitness benefits and selective pressures involved. We discuss how the lack of such comprehensive information limits our ability to fully evaluate how cognitive traits affect fitness, and to explore their demographic and evolutionary consequences. To bridge the gap between micro- and macroevolutionary processes, we also emphasize the need to better integrate individual-based research with broader population and species comparative analyses. By refining and expanding the approach, individual-based studies can deepen our insight into the evolutionary forces that have given rise to the remarkable diversity of minds across the animal kingdom.This article is part of the Theo Murphy meeting issue 'Selection shapes diverse animal minds'.

Keywords: Bogert effect; fitness; natural selection; phylogenetic-based analyses; problem-solving; spatial memory.

Figure 1.

Cognition and decision-making in elephants. African elephants may consume up to 150 kg of food and drink 70−200 l of water daily. To meet these demands, they rely on mental maps of food patches and water sources across vast areas, and can recognize and consume around 90% of the plant species in their habitat [2,3]. In dry environments, some elephants have even learnt to dig for water using their trunks, and cover the holes with leaves to reduce evaporation. As elephants live in cohesive social groups, they can learn from experienced individuals to improve decision-making [4]. Given their long lifespans and the ecological impact of their foraging, regularly updating knowledge and refining skills is essential, as the conditions they currently face may differ significantly from those they will encounter in the future. Thus, flexible, experience-based decision-making is key for elephants to survive and reproduce in their harsh environments [3]. Photo: Daniel Sol.

Figure 2.

Framework for understanding the fitness consequences of cognition. Animal decision-making is primarily guided by cognitive processes in the brain, which are shaped by a variety of genes (g₁, g₂, …, g_n) and environmental factors (A). Decisions are further influenced by the acquired knowledge retained in the memory, and by non-cognitive traits such as motor abilities and emotional responses. When faced with environmental or social challenges (e.g. a food shortage), the decisions made by the animal can generate behavioural responses that mitigate these challenges (e.g. adopting a new foraging technique) (B). The new knowledge and skills can be stored in memory, enhancing future decisions and behavioural responses (C). Behavioural performance directly influences one or more fitness components (e.g. reducing adult mortality caused by food shortages) (D). The overall impact on fitness also depends on the effect of other phenotypic traits and life-history trade-offs. For instance, improving survival can come at the cost of reducing fecundity. Cognition is considered adaptive if it enhances overall fitness (E). Specifically, the trait must, on average, enable individuals to leave at least one offspring to replace themselves—this is the concept of absolute fitness (W), commonly used in population ecology and defined as the total number of offspring an individual contributes to the next generation. For cognition to evolve, it must also confer a fitness advantage to the individual relative to other individuals from the population, described as relative fitness (w), a concept central to evolutionary biology. Demographic and evolutionary consequences, in turn, influence the alignment of the population to its environment, either by improving the average performance of individuals or by modifying the environment. For example, improved fitness might lead to higher population density, intensifying competition for resources such as food (F). In the diagram, solid lines represent the primary pathways linking cognition to demographic and evolutionary outcomes, while dotted lines highlight factors that influence these pathways. Double arrows indicate trade-offs.

Figure 3.

Importance of relative and absolute fitness to understand the adaptive nature of a trait. Absolute and relative fitness are interconnected, as natural selection acts on genetic variation among individuals to optimize the alignment between an organism’s phenotype and its environment. By enhancing this match, selection increases the average absolute fitness of a population. However, understanding whether a trait is adaptive requires distinguishing the implications of absolute and relative fitness. From the perspective of absolute fitness, a population that is stable or growing (W ≥ 1) can be considered well adapted to current conditions, while a declining population (W < 1) suggests maladaptation. Therefore, both absolute and relative fitness can provide evidence of a trait’s adaptiveness, but only in scenarios where the population is stable or growing. A declining population cannot be considered well adapted to present conditions, even when the individuals with the trait exhibit higher relative fitness (variation in w > 0). This does not imply that the trait is inherently non-adaptive: a trait may have evolved as an adaptation even if its original function is no longer critical. However, in such cases, there is less direct evidence to support its adaptive nature.