To understand the evolution of general intelligence, Burkart et al. endorse a “cultural intelligence approach,” which emphasizes the critical importance of social interaction. We argue that theory of mind provides an essential foundation and shared perspective for the efficient ontogenetic transmission of crucial knowledge and skills during human development and, together with language, can account for superior human general intelligence.

Burkart et al. consider that the relationship between general intelligence and socio-cognitive abilities is poorly understood in animals and humans. We examine this conclusion in the perspective of an already substantial evidence base on the relationship among general intelligence, theory of mind, and emotional intelligence. We propose a link between general intelligence and socio-cognitive abilities within humans.

The theory of multiple intelligences (MI) seeks to describe and encompass the range of human cognitive capacities. In challenging the concept of general intelligence, we can apply an MI perspective that may provide a more useful approach to cognitive differences within and across species.

Burkart et al.'s proposal is based on three false premises: (1) theories of the mind are either domain-specific/modular (DSM) or domain-general (DG); (2) DSM systems are considered inflexible, built by nature; and (3) animal minds are deemed as purely DSM. Clearing up these conceptual confusions is a necessary first step in understanding how general intelligence evolved.

We strongly agree that general intelligence occurs in many animals but find the cultural intelligence hypothesis of limited usefulness. Any viable hypothesis explaining the evolution of general intelligence should be able to account for it in all species where it is known to occur, and should also predict the conditions under which we can develop machines with general intelligence as well.

This commentary contrasts evolutionary plausibility with empirical evidence and cognitive continuity with radiation and convergent evolution. So far, neither within-species nor between-species comparisons on the basis of rigorous experimental and species-appropriate tests substantiate the claims made in the target article. Caution is advisable on meta-analytical comparisons that primarily rely on publication frequencies and overgeneralizations (from murids and primates to other nonhuman animals).

The qualitative division between domain-general and domain-specific cognition is unsubstantiated. The distinction is instead better viewed as opposites on a gradual scale, which has more explanatory power and fits current empirical evidence better. We also argue that causal cognition may be more general than social learning, which it often involves.

The argument by Burkart et al. in the target article relates to fluid (not general) intelligence: a domain-general ability involved in complex, novel problem solving, and strongly related to working memory and executive functions. A formative framework, under which the general factor of intelligence is the common consequence, not the common cause of the covariance among tests is more in line with an evolutionary approach.

Does general intelligence exist across species, and has it been a target of natural selection? These questions can be addressed with genomic data, which can rule out artifacts by demonstrating that distinct cognitive abilities are genetically correlated and thus share a biological substrate. This work has begun with data from humans and can be extended to other species; it should focus not only on general intelligence but also specific capacities like language and spatial ability.

Burkart et al.'s impressive synthesis will serve as a valuable resource for intelligence research. Despite its strengths, the target article falls short of offering compelling explanations for the evolution of intelligence. Here, we outline its shortcomings, illustrate how these can lead to misguided conclusions about the evolution of intelligence, and suggest ways to address the article's key questions.

The search for general processes that underlie intelligence in nonhumans has followed two strategies: one that concerns observing differences between nonhuman species (G), the second that concerns observing individual differences within a nonhuman species (g). This commentary takes issue with both attempts to mark a general factor: Differential responding to contextual variables compromises the search for G, and the lack of predictive validity compromises g.

In this commentary, we support a complex, mosaic, and multimodal approach to the evolution of intelligence. Using the arcuate fasciculus as an example of discontinuity in the evolution of neurobiological architectures, we argue that the strict dichotomy of modules versus G, adopted by Burkart et al. in the target article, is insufficient to interpret the available statistical and experimental evidence.

Across taxonomic subfamilies, variations in intelligence (G) are sometimes related to brain size. However, within species, brain size plays a smaller role in explaining variations in general intelligence (g), and the cause-and-effect relationship may be opposite to what appears intuitive. Instead, individual differences in intelligence may reflect variations in domain-general processes that are only superficially related to brain size.

We discuss the evolutionary implications of connections drawn between the authors' learned “secondary modules” and the habit-formation system that appears to be ubiquitous among vertebrates. Prior to any subsequent coevolution with social learning, we suggest that aspects of general intelligence likely arose in tandem with mechanisms of adaptive motor control that rely on basal ganglia circuitry.

We argue that the truly unique aspect of human intelligence is not the variety of cognitive skills that are ontogenetically constructed, but rather the capacity to decide when to develop and apply said skills. Even if there is good evidence for g in nonhuman animals, we are left with major questions about how the disposition to think analytically can evolve.

The authors evaluate evidence for general intelligence (g) in nonhumans but lean heavily toward mammalian data. They mention, but do not discuss in detail, evidence for g in nonmammalian species, for which substantive material exists. I refer to a number of avian studies, particularly in corvids and parrots, which would add breadth to the material presented in the target article.

Burkart et al. contend that general intelligence poses a major evolutionary puzzle. This assertion presupposes a reification of general intelligence – that is, assuming that it is one “thing” that must have been selected as such. However, viewing general intelligence as an emerging property of multiple cognitive abilities (each with their own selective advantage) requires no additional evolutionary explanation.

Burkart et al. conflate the domain-specificity of cognitive processes with the statistical pattern of variance in behavioural measures that partly reflect those processes. General intelligence is a statistical abstraction, not a cognitive trait, and we argue that the former does not warrant inferences about the nature or evolution of the latter.

The target article provides an anthropocentric model of understanding intelligence in nonhuman animals. Such an idea dates back to Plato and, more recently, Lovejoy: On Earth, humans are at the top and other animals at successively lower levels. We then evaluate these other animals by our anthropocentric folk theories of their intelligence rather than by their own adaptive requirements.

Are the mechanisms underlying variations in the performance of animals on cognitive test batteries analogous to those of humans? Differences might result from procedural inconsistencies in test battery design, but also from differences in how animals and humans solve cognitive problems. We suggest differentiating associative-based (learning) from rule-based (knowing) tasks to further our understanding of cognitive evolution across species.