Burkart et al.'s review of studies involving g and G in animals is illuminating. However, the authors seem to assume that a century of studies settled the question of g in humans. In this commentary, we challenge this assumption. We suggest that the definition of intelligence (Gottfredson Reference Gottfredson1997) cited by the authors seems to be overly anthropocentric: It emphasizes skills characteristic of Homo sapiens. This very definition appears to constrain g in humans and, in our opinion, limits its generalizability in a biological context. Furthermore, the old debate about the cultural fairness of intelligence testing is testimony to the vicissitudes of defining and measuring g in humans.
As an alternative, we propose a description of intelligence in a biological context, inspired by the work of Piaget, who suggested that “Intelligence is an adaptation … The organism adapts itself by materially constructing new forms to fit them into those of the universe, whereas intelligence extends this creation by constructing mental structures which can be applied to those of the environment” (Piaget Reference Piaget1952, pp. 3–4). Thus, intelligence is the ability of a species to adapt flexibly to many environmental challenges in the service of survival. Note that this definition is species relative: It follows naturally that the larger the range of environmental conditions to which an organism can potentially adapt, the more intelligent it might be relative to other organisms with more limited repertoire of adaptations (Piaget Reference Piaget1971).
Furthermore, we propose that intelligence is not a trait. Rather, it is the inference by the human observer in the face of increasing the potential and scope of domain-specific skills developed by species in adapting to a variety of environmental pressures. These domain-specific skills allow for increasing the range of environments to which the organism is able to respond efficiently. Of course, the converse is also the case: Environmental changes will result in adaptation by the emergence of new domain-specific skills. Such increase is the consequence of evolving ever-larger brains, especially frontal lobes, which enables the development of an ever-greater repertoire of skills (Parker & Gibson Reference Parker and Gibson1977). Moreover, a procedure or skill developed specifically within a specific domain might become accessible to systems or brain structures that serve other domains (Anderson Reference Anderson2010). Such change in accessibility creates domain-general skills or procedures, thus improving intelligence (or adaptability) (Rozin Reference Rozin, Sprague and Epstein1976). The result appears to be g to the human observer. Lest we revert again to an overly anthropocentric view, we emphasize that increasing brain size is just one means of increasing survivability.
Instead of the mysterious g factor, we propose that G is reflected in a capacity: object manipulation in various species, with its evolution into a mental manipulation (MM) in humans – the hallmark of human activity. MM can be investigated by various tests using verbal, mathematical, or spatial manipulation of contents. These tests tend to correlate positively not because they reflect g, but because they reflect MM. We suggest that MM is the ability to perform transformations on concrete and abstract objects (e.g., mental rotation) and imagine the results, without needing the actual objects. This ability clearly improves adaptability to a wide range of environments. One example of MM is when a child learns to consider a situation from the perspective of another person. We claim that linguistic construction, as well as other cognitive processes, involves MM, so that it may be considered as an overarching principle of human operations and as the basis of human culture.
To illustrate the biological continuity and the development of domain-specific skill, we consider the ontogeny of mathematical skills in humans (described originally by Piaget Reference Piaget1971). Initially, babies develop the concept of one, few, and many, requiring direct perception of objects. Animals exhibit number concept at this level (Pahl et al. Reference Pahl, Si and Zhang2013). Later, children learn that abstract symbols represent quantities, and they learn how to manipulate them. Next, algebra supplants numbers at ever higher levels of abstraction, with ever more abstract manipulations (i.e., operations). An analogous analysis was offered by Greenfield (Reference Greenfield1991) regarding the development of linguistic structures from motor schemata in children. The essence of these developmental achievements is that they reflect the ability to perform transformations, translations, recombinations, projection, predictions, and so on, in infinite ways. What is crucial for adaptation is the ability to entertain the results of these MMs, and then select only the best one for action.
One challenge to which MM could offer a positive contribution is in measuring the nebulous g. Many, if not all, IQ testing instruments may be viewed as assessing domain-specific abilities. To what extent do they reveal an underlying, domain-general or universal ability? For example, the Raven Progressive Matrices is commonly used as a measure of the g factor (Deary et al. Reference Deary, Penke and Johnson2010). However, in a wider cultural context, this test may measure no more than a domain-specific, culturally acquired skill (Owen Reference Owen1992). We suggest that MM is such an overarching set of operations. It is possible that MM started as an ability to manipulate or view actual objects designed for the visual-spatial domain. These visual-spatial specific abilities evolved to serve other domains (e.g., language) and have become accessible to other systems that serve other commitments.
In sum, we propose that the alternative conception of intelligence as offered here, compels rethinking g in humans. It is suggested that animal behavior, specifically, object manipulations, and perspective taking (a variant of MM) with increasing cortex, provide specific precursors to human abilities, as reviewed by Burkart et al. A good example of a transitional stage to MM demonstrating biological continuity is deception in apes (Byrne & Corp Reference Byrne and Corp2004).We further submit that MM may better serve as a biologically based concept for studying individual differences in humans, while providing for continuity across species.
Burkart et al.'s review of studies involving g and G in animals is illuminating. However, the authors seem to assume that a century of studies settled the question of g in humans. In this commentary, we challenge this assumption. We suggest that the definition of intelligence (Gottfredson Reference Gottfredson1997) cited by the authors seems to be overly anthropocentric: It emphasizes skills characteristic of Homo sapiens. This very definition appears to constrain g in humans and, in our opinion, limits its generalizability in a biological context. Furthermore, the old debate about the cultural fairness of intelligence testing is testimony to the vicissitudes of defining and measuring g in humans.
As an alternative, we propose a description of intelligence in a biological context, inspired by the work of Piaget, who suggested that “Intelligence is an adaptation … The organism adapts itself by materially constructing new forms to fit them into those of the universe, whereas intelligence extends this creation by constructing mental structures which can be applied to those of the environment” (Piaget Reference Piaget1952, pp. 3–4). Thus, intelligence is the ability of a species to adapt flexibly to many environmental challenges in the service of survival. Note that this definition is species relative: It follows naturally that the larger the range of environmental conditions to which an organism can potentially adapt, the more intelligent it might be relative to other organisms with more limited repertoire of adaptations (Piaget Reference Piaget1971).
Furthermore, we propose that intelligence is not a trait. Rather, it is the inference by the human observer in the face of increasing the potential and scope of domain-specific skills developed by species in adapting to a variety of environmental pressures. These domain-specific skills allow for increasing the range of environments to which the organism is able to respond efficiently. Of course, the converse is also the case: Environmental changes will result in adaptation by the emergence of new domain-specific skills. Such increase is the consequence of evolving ever-larger brains, especially frontal lobes, which enables the development of an ever-greater repertoire of skills (Parker & Gibson Reference Parker and Gibson1977). Moreover, a procedure or skill developed specifically within a specific domain might become accessible to systems or brain structures that serve other domains (Anderson Reference Anderson2010). Such change in accessibility creates domain-general skills or procedures, thus improving intelligence (or adaptability) (Rozin Reference Rozin, Sprague and Epstein1976). The result appears to be g to the human observer. Lest we revert again to an overly anthropocentric view, we emphasize that increasing brain size is just one means of increasing survivability.
Instead of the mysterious g factor, we propose that G is reflected in a capacity: object manipulation in various species, with its evolution into a mental manipulation (MM) in humans – the hallmark of human activity. MM can be investigated by various tests using verbal, mathematical, or spatial manipulation of contents. These tests tend to correlate positively not because they reflect g, but because they reflect MM. We suggest that MM is the ability to perform transformations on concrete and abstract objects (e.g., mental rotation) and imagine the results, without needing the actual objects. This ability clearly improves adaptability to a wide range of environments. One example of MM is when a child learns to consider a situation from the perspective of another person. We claim that linguistic construction, as well as other cognitive processes, involves MM, so that it may be considered as an overarching principle of human operations and as the basis of human culture.
To illustrate the biological continuity and the development of domain-specific skill, we consider the ontogeny of mathematical skills in humans (described originally by Piaget Reference Piaget1971). Initially, babies develop the concept of one, few, and many, requiring direct perception of objects. Animals exhibit number concept at this level (Pahl et al. Reference Pahl, Si and Zhang2013). Later, children learn that abstract symbols represent quantities, and they learn how to manipulate them. Next, algebra supplants numbers at ever higher levels of abstraction, with ever more abstract manipulations (i.e., operations). An analogous analysis was offered by Greenfield (Reference Greenfield1991) regarding the development of linguistic structures from motor schemata in children. The essence of these developmental achievements is that they reflect the ability to perform transformations, translations, recombinations, projection, predictions, and so on, in infinite ways. What is crucial for adaptation is the ability to entertain the results of these MMs, and then select only the best one for action.
One challenge to which MM could offer a positive contribution is in measuring the nebulous g. Many, if not all, IQ testing instruments may be viewed as assessing domain-specific abilities. To what extent do they reveal an underlying, domain-general or universal ability? For example, the Raven Progressive Matrices is commonly used as a measure of the g factor (Deary et al. Reference Deary, Penke and Johnson2010). However, in a wider cultural context, this test may measure no more than a domain-specific, culturally acquired skill (Owen Reference Owen1992). We suggest that MM is such an overarching set of operations. It is possible that MM started as an ability to manipulate or view actual objects designed for the visual-spatial domain. These visual-spatial specific abilities evolved to serve other domains (e.g., language) and have become accessible to other systems that serve other commitments.
In sum, we propose that the alternative conception of intelligence as offered here, compels rethinking g in humans. It is suggested that animal behavior, specifically, object manipulations, and perspective taking (a variant of MM) with increasing cortex, provide specific precursors to human abilities, as reviewed by Burkart et al. A good example of a transitional stage to MM demonstrating biological continuity is deception in apes (Byrne & Corp Reference Byrne and Corp2004).We further submit that MM may better serve as a biologically based concept for studying individual differences in humans, while providing for continuity across species.