The g factor, or general factor, of intelligence is a psychometric construct that summarizes observed correlations between an individual’s scores on various measures of cognitive abilities. First described in humans, a g factor has since been identified in a number of non-human species.
Non-human models of g have been used in genetic and neurological 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 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, spatial reasoning, 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,<ref>Berg, C. A., & Sternberg, R. J. (1985). "Response to novelty: Continuity versus discontinuity in the developmental course of intelligence." Advances in Child Development and Behavior, 19, 1–47.</ref> 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 reversal and inhibition 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.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 and neurochemistry. Social learning and culture may have played a large role in the evolution of intelligence 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 proximity to humans, primates (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.