The ''g'' factor, or general factor, of

intelligence Intelligence has been defined in many ways: the capacity for abstraction, logic, understanding, self-awareness, learning, emotional knowledge, reasoning, planning, creativity, critical thinking, and problem-solving. More generally, it can b ...

is a psychometric construct that summarizes observed correlations between an individual’s scores on various measures of

cognitive abilities Cognitive skills, also called cognitive functions, cognitive abilities or cognitive capacities, are brain-based skills which are needed in acquisition of knowledge, manipulation of information and reasoning. They have more to do with the mechanisms ...

. First described in

humans Humans (''Homo sapiens'') are the most abundant and widespread species of primate, characterized by bipedalism and exceptional cognitive skills due to a large and complex brain. This has enabled the development of advanced tools, culture, ...

, a ''g'' factor has since been identified in a number of non-human species.Reader, S. M., Hager, Y., & Laland, K. N. (2011). The evolution of primate general and cultural intelligence. Philosophical Transactions of the Royal Society B: Biological Sciences, 366(1567), 1017-1027. Non-human

models A model is an informative representation of an object, person or system. The term originally denoted the plans of a building in late 16th-century English, and derived via French and Italian ultimately from Latin ''modulus'', a measure. Models c ...

of ''g'' have been used in geneticPlomin, R. (2001). The genetics of ''g'' in human and mouse. Nature Reviews Neuroscience, 2(2), 136-141. and

neurological Neurology (from el, νεῦρον (neûron), "string, nerve" and the suffix -logia, "study of") is the branch of medicine dealing with the diagnosis and treatment of all categories of conditions and disease involving the brain, the spinal ...

Anderson, B. (2000). The ''g'' factor in non-human animals. The nature of intelligence, (285), 79. research on intelligence to help understand the mechanisms behind variation in ''g''.

Methods

Most measures of ''g'' in humans, including most IQ tests, rely heavily on

language Language is a structured system of communication. The structure of a language is its grammar and the free components are its vocabulary. Languages are the primary means by which humans communicate, and may be conveyed through a variety of met ...

and verbal ability, and so they cannot be directly applied to non-human animals. Several alternative measures have been developed to study intelligence in animals, relying on the observation of animals in natural situations or on behavioral tasks in experimental settings. The tasks focus on such things as innovation and problem solving, response to novelty, habit reversal and inhibition, and social learning and culture. A comprehensive assessment often includes a battery of tests involving several sorts of behavior.

Innovation & problem solving

Innovation and problem solving tasks are the most widely used experimental measures of non-human intelligence. The same assessment often uses several tasks, which may involve

memory Memory is the faculty of the mind by which data or information is encoded, stored, and retrieved when needed. It is the retention of information over time for the purpose of influencing future action. If past events could not be remembered, ...

spatial reasoning Spatial may refer to: *Dimension *Space *Three-dimensional space Three-dimensional space (also: 3D space, 3-space or, rarely, tri-dimensional space) is a geometric setting in which three values (called ''parameters'') are required to determ ...

, visual and auditory discrimination, and object manipulation. Innovation has often been observed in animals, typically involving novel solutions to everyday problems or the use of tools to achieve a goal. Instances include termite fishing in chimpanzees or nut cracking in robust capuchins. Such observations provide ecologically valid measures without the need for experimentation.

Response to novelty

Response to novelty is often used in intelligence measures in human infants, for the amount of interest in novel objects and the time spent exploring a novel environment correlate with intelligence later in life. Responses to novelty in non-humans are thought to correlate similarly, though it can often be difficult to quantify this measure appropriately.

Habit reversal & inhibition

Habit A habit (or wont as a humorous and formal term) is a routine of behavior that is repeated regularly and tends to occur subconsciously.

reversal and

inhibition Inhibitor or inhibition may refer to: In biology * Enzyme inhibitor, a substance that binds to an enzyme and decreases the enzyme's activity * Reuptake inhibitor, a substance that increases neurotransmission by blocking the reuptake of a neurotra ...

are commonly used to test primate intelligence. These tasks require the animal to suppress a learned response or instinctive action in order to receive a reward. For example, in the detour problem, a food reward behind an obstacle must be retrieved by following an indirect route. To do this, the subject must inhibit its tendency to move straight towards the goal.

Social learning

A number of intelligence tests for animals include social learning. The more an individual participates in and gains from social learning, the higher its intelligence is judged to be. Such data are most widely available for primates in social situations, often in wild populations, rather than experimental set-ups Such observations are more ecologically valid than some other measures. One basis for their inclusion in IQ studies centers around the theory of

cultural intelligence Cultural intelligence or cultural quotient (CQ) is the ability to relate and work effectively across cultures, bearing similarity to the term cultural agility. The term has been used in business, education, government, and academic research conte ...

.van Schaik, C. P., & Burkart, J. M. (2011). Social learning and evolution: the cultural intelligence hypothesis. Philosophical Transactions of the Royal Society of London B: Biological Sciences, 366(1567), 1008-1016.Herrmann, E., Call, J., Hernández-Lloreda, M. V., Hare, B., & Tomasello, M. (2007). Humans have evolved specialized skills of social cognition: the cultural intelligence hypothesis. science, 317(5843), 1360-1366.

''g'' in non-human mammals

A large portion of the research into non-human ''g'' factors has focused on mammals. Being mammals themselves, humans have a great deal in common with other mammals, sharing similarities in aspects such as

physiology Physiology (; ) is the scientific study of functions and mechanisms in a living system. As a sub-discipline of biology, physiology focuses on how organisms, organ systems, individual organs, cells, and biomolecules carry out the chemical ...

and

neurochemistry Neurochemistry is the study of chemicals, including neurotransmitters and other molecules such as psychopharmaceuticals and neuropeptides, that control and influence the physiology of the nervous system. This particular field within neuroscience e ...

. Social learning and

culture Culture () is an umbrella term which encompasses the social behavior, institutions, and norms found in human societies, as well as the knowledge, beliefs, arts, laws, customs, capabilities, and habits of the individuals in these groups.Tyl ...

may have played a large role in the

evolution of intelligence The evolution of human intelligence is closely tied to the evolution of the human brain and to the origin of language. The timeline of human evolution spans approximately seven million years, from the separation of the genus '' Pan'' until the eme ...

in humans (including its factor structure) and as such it follows that other animals may have similar single-factor models of intelligence.

Primates

Due to their close

taxonomic Taxonomy is the practice and science of categorization or classification. A taxonomy (or taxonomical classification) is a scheme of classification, especially a hierarchical classification, in which things are organized into groups or types. ...

proximity to humans,

primates Primates are a diverse order of mammals. They are divided into the strepsirrhines, which include the lemurs, galagos, and lorisids, and the haplorhines, which include the tarsiers and the simians (monkeys and apes, the latter including huma ...

( great apes in particular) have been the focus of a large part of the research into the prevalence of a ''g'' factor in non-human animals. A

meta-analysis A meta-analysis is a statistical analysis that combines the results of multiple scientific studies. Meta-analyses can be performed when there are multiple scientific studies addressing the same question, with each individual study reporting me ...

of 4,000 primate behaviour academic papers searching for instances of

innovation Innovation is the practical implementation of ideas that result in the introduction of new goods or services or improvement in offering goods or services. ISO TC 279 in the standard ISO 56000:2020 defines innovation as "a new or changed entity ...

, social learning,

tool use Tool use by animals is a phenomenon in which an animal uses any kind of tool in order to achieve a goal such as acquiring food and water, grooming, defence, communication, recreation or construction. Originally thought to be a skill possessed o ...

, and extractive foraging was conducted to investigate the components of these behaviours in 62 species of primates. A

principal component analysis Principal component analysis (PCA) is a popular technique for analyzing large datasets containing a high number of dimensions/features per observation, increasing the interpretability of data while preserving the maximum amount of information, and ...

of these cognitive measures (as well as three socio-ecological variables, (diet breadth, percentage fruit in diet, and group size) revealed a single factor explaining 47% of the variance onto which the cognitive measures and diet breadth (somewhat) loaded. This would suggest that non-human primates, as a whole, have a ''g'' factor similar to that observed in humans.

Rodents

Mice A mouse ( : mice) is a small rodent. Characteristically, mice are known to have a pointed snout, small rounded ears, a body-length scaly tail, and a high breeding rate. The best known mouse species is the common house mouse (''Mus musculus' ...

and

rats Rats are various medium-sized, long-tailed rodents. Species of rats are found throughout the order Rodentia, but stereotypical rats are found in the genus ''Rattus''. Other rat genera include ''Neotoma'' (pack rats), ''Bandicota'' (bandicoot ...

have been used as

model organisms A model organism (often shortened to model) is a non-human species that is extensively studied to understand particular biological phenomena, with the expectation that discoveries made in the model organism will provide insight into the working ...

in research for hundreds of years and have been a staple of

experimental psychology Experimental psychology refers to work done by those who apply experimental methods to psychological study and the underlying processes. Experimental psychologists employ human participants and animal subjects to study a great many topics, in ...

for decades. Both have been proposed as easily accessible models for studying ''g''. The ''g'' factor loadings in

Long-Evans A laboratory rat or lab rat is a brown rat of the subspecies '' Rattus norvegicus domestica'' which is bred and kept for scientific research. While less commonly used for research than mice (see laboratory mouse), rats have served as an impor ...

rats has been shown to range from .43 to as high as .70 in cognitive ability tasks. In mice, about 55–60% of the individual variance in tests of cognitive ability can be explained by ''g''.

Applications

Genetic research

Non-human

of intelligence can be used in individual differences research for study designs that are difficult or unethical to perform using human subjects. Examples of this include experimental drug testing and multi-generational studies that would take a very long time in humans. One such aspect of intelligence well suited for a non-human model is the experimental study of genetic aspects of ''g''.

are currently being considered as a potential model due to their widespread availability, detailed knowledge of their

genome In the fields of molecular biology and genetics, a genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding ge ...

, and the ease with which strains can be bred to exhibit individual differences in

cognitive ability Cognitive skills, also called cognitive functions, cognitive abilities or cognitive capacities, are brain-based skills which are needed in acquisition of knowledge, manipulation of information and reasoning. They have more to do with the mechanisms ...

Neuroscience

Non-human models can also be used in

neuroscience Neuroscience is the scientific study of the nervous system (the brain, spinal cord, and peripheral nervous system), its functions and disorders. It is a multidisciplinary science that combines physiology, anatomy, molecular biology, development ...

for

neuroanatomical Neuroanatomy is the study of the structure and organization of the nervous system. In contrast to animals with radial symmetry, whose nervous system consists of a distributed network of cells, animals with bilateral symmetry have segregated, defi ...

studies investigating intelligence and the influence of ''g'' on the neurological level. Rats have been used in experimental manipulations of intelligence using chemicals administered prenatally. These effects are partially reversed by stimulation of neurological development and suggest that neuronal and synaptic numbers have an effect on ''g''.

Criticism

A 2012 study identifying individual chimpanzees that consistently performed highly on cognitive tasks found clusters of abilities instead of a general factor of intelligence. This study used individual-based data and claim that their results are not directly comparable to previous studies using group data that have found evidence for ''g''. The authors propose a future research should test multiple individuals of multiple species on a variety of tasks to investigate this discrepancy. A 2020 review and meta-analysis of ''g'' in non-humans found that the average correlation between cognitive tasks was 0.18, suggesting weak support for general intelligence. This study also highlighted limitations of factor-analytic procedures used to extract a single 'general' factor of intelligence and found that previous studies often failed to test critical assumptions of their methods. The authors suggest that future research should focus on patterns of (co)variance among cognitive abilities''.''

References

{{Reflist, 2 Animal intelligence Psychometrics