General intelligence: what is it and how has it evolved?

One of the most important debates in approaching the evolution of human intelligence is whether humans have developed a single general intelligence (og) or, conversely, an intelligence divided into a set of specializations.

Some of the literature attributes the first to humans and the second to non-human animals, but as always in science, not everything is so simple and there are studies that provide data against this idea.

On this debate, Judith M. Burkart and her colleagues at the University of Zurich conducted a review in 2017 in which they assessed the presence of g in non-human animals and explored its implications for theories of the evolution of cognition.

    How is the intelligence of humans and animals?

    In humans, we can understand intelligence through the ability to reason, plan, solve problems, or think in an abstract way, among other abilities. In animals, it has been defined instead by the ability to acquire knowledge about the physical or social environment and to use it to solve new problems.

    But What does it mean that a species has general intelligence? At the empirical level, we speak of general intelligence when the individuals of the species obtain similar scores on different types of cognitive tasks (such as causal reasoning or social learning tasks), giving rise to the famous g factor. Or, in other words, that there is a significant correlation between some scores and others.

    This is called a positive manifold, and this is the big argument for the presence of g in humans. Another is the correlation of g with brain size, gray matter volume, and cortical thickness, as well as academic and professional achievement, among others. In summary, the presence of a general intelligence in humans is represented by the factor and finds support both in neurobiology and in characteristics of the life of individuals.

    The alternative, or perhaps complementary, view of general intelligence is to speak of modular intelligence. Intelligence based on specialized modules for different cognitive skills. The evolutionary basis of this concept is to consider these modules as cognitive adaptations to problems that have been repeated over a long period during the evolution of a species.

    In this context, the solutions to these problems would have been channeled through natural selection. An example would be for a species to develop a great spatial memory when it has historically needed to find food in large, complex territories. Therefore, according to this point of view, human and animal spirits can be seen as a set of specializations that have arisen to respond to specific problems in the environment.

    In the past, a very strict modular mind concept was advocated, with modules or independent intelligences processing information with different “input channels”. This vision is totally incompatible with the presence of a general intelligence in the same individual. however, recently many authors propose the compatibility of these modules with a “central system” of information processing. and, in turn, with a general intelligence.

    But if this central system has only been demonstrated in humans, the key question regarding the evolution of general intelligence would be how it appeared, during human evolution, on a previously existing modular system. . To answer this question, we need to study the cognitive characteristics of non-human animals.

    General intelligence in non-human animals

    The vast majority of studies that have attempted to find g in non-human animals have been conducted primarily in rodents and primates, especially great apes. In rodents, the presence of g appears to be quite robust, with studies examining up to 8 different spots in mice and rats. As for non-human primates, the results are rather mixed:

    Some studies, mainly focused on chimpanzees, have found alternatives to the g factor to explain the intelligence of this species. An example is that of Esther Herrmann and her collaborators who, applying similar intelligence tests to chimpanzees and human children, find that it is organized differently according to the species. Children’s performance was best explained through three different modules, or intelligences (spatial, physical and social). On the other hand, “the intelligence of chimpanzees” was best explained by two factors: one spatial and a second grouping both physical and social tasks).

    Subsequent studies such as that by Herrmann and Call i Amici and colleagues find similar results (no presence of g) in chimpanzees and at the interspecific level, respectively.

    In contrast, other authors have advocated the presence of general intelligence in chimpanzees after finding characteristics shared with humans. William D. Hopkins and collaborators at Georgia State University discovered that intelligence is largely inherited in chimpanzees. Additionally, the g factor has been linked to larger brains and thicker cortex in this species, and Beran and Hopkins found a strong correlation between g and scores in self-monitoring tasks.

    Although the presence of g in great apes is still debated, these studies raise the possibility that general intelligence is not exclusive to the human species. In support of this idea, most studies that have investigated the presence of general intelligence at the interspecific (or G) level find evidence for it.

    So how has general intelligence evolved?

    The fact that a large part of the studies support the presence of general intelligence in rodents and primates leads us to suggest that it developed in certain lineages above or, perhaps at the same time, than specific adaptive capacities, theoretically easier to model by natural selection.

    Here comes into play a component directly correlated with general intelligence: the size of the brain. Just as specific abilities (however sophisticated they may become) did not require a great deal of brain expansion, it appears that species with more general intelligence did need a significant increase in brain tissue.

    But, What are the conditions that led these species to possess these abilities? One proposal that seeks to answer this question is the cognitive buffer hypothesis, which considers innovation and learning as two main drivers of the development of general intelligence. Based on this idea, species whose environment usually changes or becomes unpredictable would have required general intelligence to cope with unusual or changing ecological difficulties. Examples in favor of this theory would be the correlation between more innovative species with a greater presence of G in primates, or the fact that a higher proportion of “colonization success” was found in species with larger brains (including birds, mammals, amphibians, reptiles and fish).

    If we are to believe this hypothesis, the most logical would be to wonder why all species have not ended up developing this intelligence that would allow them to adapt to all kinds of environments. Well, the answer lies in the high costs involved. Brain expansion that requires this type of adaptation involves a huge energy cost (remember that in humans the brain can consume up to 20% of the energy needed by the whole body) which also requires a slowing of physical and cerebral development at the ontogenetic level. level.

    Under these conditions, only species capable of providing special and lasting care to young adults would have the capacity to allow such sacrifice. In this scenario would play an important role both the absence of constant predators that threaten the survival of adults and the care allomaternal (reproductive care by, in addition to the mother, other individuals of the group) which present many species, especially primates.

    This explanation coincides with the well-known hypothesis of Michael Tomasello that social intelligence gives importance to social learning and is responsible, to a large extent, for brain expansion and high cognitive abilities of the human race.

    In conclusion, this review leads us to accept (or at least to consider) the compatibility between specialized cognitive abilities and general intelligence. At this point, it might be more interesting and correct to ask which skills emerge by specialization and which are the result of further adaptation through the cognitive flexibility that accompanies general intelligence. In this sense, and as always in science, more comparative studies are needed to understand when and why ga evolved.

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