Intelligence

 Humans, the most numerous large land animal on Earth, exercise an extensive but limited dominance over the surface of the planet’s crust. In the two million or so years in which their genus has existed, they have spread over the Earth’s continents, and have adapted to an astounding array of different environments. The evolution of Homo Sapiens some 250,000-300,000 ybp saw a vast expansion of human knowledge and skills, an expansion which has made humans—at least temporarily—the most advanced species in the biosphere. Through means of society and culture, humans have passed what they have learned (or think they have learned) to those born after them.

The human ability to learn is extraordinary, as we have just seen. Many factors, of course, affect this ability. Key among these is intelligence, one of the more complex subjects in human psychology. It is human intelligence that has given our species the ultimate advantage over the rest of Kingdom Animalia. But the definition of this trait, and the study of how individual humans come to possess it, are areas riven by disputes.

The Many Definitions of Intelligence

In its broadest definition, intelligence might be thought of as the ability to understand a situation, recognize challenges and problems that may be associated with that situation, and take appropriate action in a timely manner to deal with them. (That appropriate action can sometimes be to do nothing.) A team of brain researchers has given a more formal definition:

…‘intelligence’ can be understood as mental or behavioural flexibility or the ability of an organism to solve problems occurring in its natural and social environment, culminating in the appearance of novel solutions that are not part of the animal's normal repertoire. This includes forms of associative learning and memory formation, behavioural flexibility and innovation rate, as well as abilities requiring abstract thinking, concept formation and insight.¹

It should be noted immediately that there is no universally accepted definition of intelligence. (One indefatigable researcher has found no fewer than 71 different definitions.)² A prominent neuroscientist has noted that most definitions center around the concept of problem solving. As he puts it, “More complex problems require higher levels of intelligence. For example, it requires more intelligence to be able to solve differential equations than simply to be able to add two single-digit numbers.”³  It should also be noted that the definition of intelligence is not limited solely to the ability to master academic subjects. Intelligence has much broader applications.

In 1983 the American psychologist Howard Gardner published his theory of multiple intelligences. Gardner saw nine specialized forms of intelligence, or areas in which different sets of intellectual skills were required. They are as follows:

Verbal-linguistic intelligence

Logical-mathematical intelligence

Spatial-visual intelligence (the ability to think in pictures and visualize possibilities)

Bodily-kinesthetic intelligence (particular to athletics)

Musical intelligences

Interpersonal intelligence (the ability to relate effectively to others)

Intrapersonal (self-examination)

Naturalist intelligence (recognizing and categorizing elements of the natural world)

Existential intelligence (the ability to think about “big” issues)⁴

Gardner’s ideas have come under criticism from many sources. Some see Gardner’s categories as simply a list of different talents people have with the word “intelligence” tied to them. Others contend that Gardner’s ideas are not truly scientific but are rather a neuromyth. One critic defines the term neuromyth as “a commonly accepted but unscientific claim about brain function.”⁵ Gardner’s work, in her view, was based on an understanding of the brain’s physiology that has been superseded, and that his hypothesis is not supported by empirical data.

Gardner’s MI theory was not a neuromyth initially because it was based on theories of the 1980s of brain modularity for cognition, and few researchers then were concerned by the lack of validating brain studies. However, in the past 40 years neuroscience research has shown that the brain is not organized in separate modules dedicated to specific forms of cognition.⁶

I think it would therefore be fair to say that Gardner identified various ways that intelligence is manifested rather than distinct kinds of intelligence that arise from areas of the brain dedicated to these manifestations.

There is a distinction between crystallized intelligence and fluid intelligence. This idea was first formulated by the psychologist Raymond Cattell in 1943. To put it succinctly, crystallized intelligence is the sum of what one has learned and one’s ability to bring this knowledge to bear when required. Fluid intelligence is the ability to deal with novel problems and new situations, situations in which previously learned information cannot be applied. In Cattel’s view, crystallized intelligence can be increased throughout adult life (unless senescence ends this accumulation of knowledge) while fluid intelligence is most critical in childhood and adolescence and plateaus in young adulthood.⁷

Neural Correlates of Intelligence

A great deal of research has been done to determine which areas of the human brain are most closely associated with intelligence. Two brain researchers in the UK, referring to the contention “that the cognitive basis of intelligence is the ability to make fluid or creative analogical relationships between distantly related concepts or pieces of information”⁸, decided to use functional magnetic resonance imaging (fMRI) to examine subjects engaged in tasks requiring the ability to make analogies. Their findings:

An analysis using covariates determined per subject by analogical depth revealed significant bilateral neural activations in the superior, inferior, and middle frontal gyri and in the anterior cingulate/paracingulate cortex. These frontal areas have been previously associated with reasoning tasks involving inductive syllogisms, syntactic hierarchies, and linguistic creativity.⁹

In 2009, a team of neurologists from UCLA published an overview of the ways in which advanced scanning technologies can be used to ascertain intelligence levels in humans. Based on their wide-ranging, multi-sourced research, they attempted to identify those anatomical features of the brain that affect the level of an individual’s intelligence. These scientists stressed that what they were observing were correlations, and that conclusions about the relationship between the brain’s anatomy and human intelligence remain speculative. With these caveats in mind, what factors and brain regions may have an influence on intelligence? One of these is overall brain volume, with important reservations. It is the authors’ opinion that “increased global brain volumes observed in more intelligent individuals may be accounted for by selectively enlarged volumes in brain regions especially relevant for higher cognitive function”.¹⁰ Other regions and factors include the frontal, temporal, and parietal lobes, the hippocampus, the cerebellum, significant volumes of gray matter (particularly in the lateral and medial frontal cortex), cortical thickness, and the thickness of the corpus callosum.¹¹

General Indicators of Intelligence

The rapidity, accuracy, and/or scope of one’s situational awareness, comprehension, knowledge base, and logical abilities are measurable aspects of intelligence, although the methods used to measure them are sometimes controversial. (This discussion is not the place to examine the controversies over these measures.) As we saw, Gardner’s neuromyth gives us an overview of the ways in which humans exhibit intelligence. Looking more deeply, we can say that the ability of a human brain to deal with abstract ideas and the language needed to express them, the ability to command language in general and use it effectively, the ability to reasonably predict immediate outcomes of actions, the ability to apply reason and precedent to novel or unexpected situations, the ability to conceive of possible realities and assess the degree of their probability, the ability to focus on the most salient aspects of a situation or problem, and the ability to adapt quickly to a given set of circumstances are, I think, the foundations of our intellectual prowess.

Overall, the meta-talent of the human species is, as I have already said, its adaptability. Not all individuals will display this quality, but as a collectivity, our ability to change with changing circumstances has been our most vital survival asset. Human intelligence gives us a vast superiority over most living things. Humans, as a group, can often change in something very close to real time (when measured in geological terms). Most living things can only change in evolutionary time, meaning that the processes of natural selection and genetic drift must act with their characteristic slowness to allow them to adapt. Moreover, human intelligence can deal with an impressive variety of challenges. As we have seen, many animals exhibit intelligence. But it is the range and depth of human intelligence that has given us our limited power over the biosphere.

Intelligence, Both Heritable and Malleable

In Volume One (p. 433) we saw there is evidence that, to a degree, intelligence is heritable. The fact of intelligence’s heritability is not really in question, but rather the degree to which it is heritable and the role of environmental/cultural factors in the shaping of intellect. Two neuroscientists researching this issue have arrived at a conclusion that I think warrants attention. They contend that intelligence is the result of the interaction of genetic and environmental factors.

The high heritability of intelligence could have emerged from independent genetic effects, while its high malleability could have arisen from independent environmental effects. However, in isolation, these possibilities have little explanatory value. Accordingly, since intelligence is demonstrably malleable, independent genetic effects cannot possibly run the show. Likewise, since intelligence is demonstrably heritable, independent environmental effects cannot possibly run the show. This leads us to the conclusion that gene-environment interplay is the ring master. [My emphasis.]While seemingly straight-forward, this conclusion has been sublimated by methodological/conceptual biases (the first dibs to genetics) and its elusive nature (the hidden iceberg of interactions). Here, we have presented evidence that the GE solution is theoretically and empirically sound, even though at first glance it seems improbable. Paraphrasing Sherlock Holmes’ maxim: since we have eliminated the now implausible options, whatever remains, however well hidden, must be the truth (or at least a closer approximation).¹²

There has been extensive research done on the degree of genetic influence on intelligence, and although research methodologies have been improved, there is still no definitive answer to the (perhaps meaningless) question, “What is the exact percentage of intelligence accounted for by genetic influences?” A pair of scientists in the UK have looked deeply at this issue, and they report the following:

A.  The degree of heritability is not fixed, but rather increases in a linear fashion over time. It rises from about 20% in infancy to 60% in adulthood. What seems to account for this is something known as genetic amplification. This is to say that genetic propensities in children are amplified by the ways in which these children arrange and organize their environment. The implication, in my view, is that as people mature, and the ways in which they arrange their environments become more elaborate, the more indicative of their genetic inheritance these arrangements become.

B. Genetic differences in intelligence are largely attributable to those genes that influence cognitive abilities such as vocabulary, memory, and the brain’s executive functions. These genes display a high level of pleiotropy [when a single gene can have multiple effects].

C.  Assortative mating has a major impact on intelligence levels. Assortative mating is the tendency of people to marry and mate with people who are similar to them. On the scale in which 0.00 equals no correlation and 1.00 equals absolute correlation, assortative mating for intelligence is about 0.40 for intelligence generally and about 0.50 for verbal intelligence. (By way of comparison, the correlation for height and weight is about 0.20.) Interestingly, there is about a 0.60 correlation for years of education. Further, inbreeding has a negative effect on intelligence.¹³

If, indeed, environmental factors play a role in intelligence, what factors seem to be the most significant ones? A team of medical researchers in India, after studying a large sample of children, came to these conclusions:

In the present study, we found that various environmental factors such as place of residence, physical exercise, family income, parents' occupation and education influence the IQ of a child to a great extent. Hence, a child must be provided with an optimal environment to be able to develop to his/her full genetic potential.¹⁴

Research indicates that adequate early childhood nutrition is an important factor in good cognitive development.¹⁵ The educational level of parents is a factor in their children’s cognitive development.¹⁶ Family stability is also key. A Princeton University study indicates that stability is a major factor in cognitive development. Interestingly, an unstable two parent home is not as good in this regard as a stable single-parent home.¹⁷

It should also be noted that research finds no significant difference between the intelligence of women and that of men. Further, the assertion that one “race” (a specious term, in my view) is naturally intellectually superior to others, is an idea that finds no broad scientific support.¹⁸ And it bears repeating that the assertion that humans “only use 10% of their brain” is complete nonsense.

The Critical Junctures in the Rise of Human Intelligence

In tracing the evolution of the anatomically modern human, the evolution of the human brain, and the rise and manifestations of human consciousness, we have largely traced the rise of human intelligence. Those studying these phenomena have looked for certain critical junctures in the history of intellect’s development. We have already come across Merlin Donald’s hypothesis about the significance of self-triggered recall and rehearsal loop in the evolution of memory (pp. 617-618). As I have already noted, tool making gave a selective advantage to imaginative thinking. Human social life’s increasing complexity worked in a reciprocal way with the evolution of the brain, and the advent of gestural and vocal communication gave a strong selective advantage to those who mastered these skills. We can say that the transition from Homo erectus to Homo sapiens (taking into account the crucial offshoot from erectus of Homo heidelbergensis, the African variant of which might be the true precursor to sapiens) was the biggest juncture of all in the development of human intelligence. We face the world with, essentially, the same sensory and cognitive apparatus with which a Homo sapiens tribe in prehistoric Ethiopia or southern Africa faced it.

Human intelligence was also affected by the oral history and storyteller traditions, which put a premium on training the memory, and the rise of written symbols and the storage of information outside of the human body. Research indicates that reading and writing use existing brain structures, repurposing them. Stanislas Dehaene explains this:

…new cultural inventions such as writing are only possible inasmuch as they fit within our preexisting brain architecture. Each cultural object must find its neuronal niche—a set of circuits that are sufficiently close to the required function and sufficiently plastic to be partially “recycled.” The theory stipulates that cultural inventions always involve the recycling of older cerebral structures that originally were selected by evolution to address very different problems but manage, more or less successfully, to shift toward a novel cultural use.

How can this view explain why all readers possess a specialized and reproducibly located area for a recent cultural invention? The idea is that the act of reading is tightly constrained by the preexisting brain architectures for language and vision. The human brain is subject to strong anatomical and connectional constraints inherited from its evolution, and the crossing of these multiple constraints implies that reading acquisition is channeled to an essentially unique circuit.¹⁹

The evidence shows that even under the constraints imposed by the need to repurpose existing brain anatomy, reading can have a major impact on intelligence. Research on identical twins has revealed that reading improves both verbal and non-verbal cognitive abilities in children.²⁰

Consequences of Intelligence

Our intelligence, as noted, has allowed us to dominate the other animal species, with consequences that are, in the long run, unpredictable. As we will examine more closely in the next volume of this work, human intelligence has created amazingly complex societies and cultures. But these societies and cultures also, almost paradoxically, display the limits and fallibility of human intelligence. Humans have created social and cultural entities that are utterly beyond their ability to fully understand. Individual humans very often find themselves struggling to navigate life in such societies, often overwhelmed by the contradictions and randomness they encounter. We have unintentionally created situations that may be beyond our ability to stabilize or correct. It is the sense among some of us that we will require a non-human intelligence to pull us out of these difficult situations that has given rise to machine “intelligence”—a move which might be even more dangerous than the situations the machines have been devised to rectify.

Moreover, humans have often tended to overestimate their own intelligence. This has led many of them to have an unwarranted sense of certainty. Others have been held back by deficiencies in their intellect, and have often been unfairly dealt with by those taking advantage of these deficiencies. Both in evolution and in everyday human life, intelligence is a survival advantage.

But our intelligence is not absolute, and everywhere we turn, we run into its limits. One of the ways the human mind tries to find these limits and gain control of complex situations is through the processes of reasoning. It is to the operations of reasoning we now turn, mindful that even the most patiently reasoned chains of thought can lead us in unexpected directions—or even dead ends.

1.   https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4685590/

2.   https://calculemus.org/lect/08szt-intel/materialy/Definitions%20of%20Intelligence.html

3.  Lee, Daeyeol. Birth of Intelligence: From RNA to Artificial Intelligence (p. 4). Oxford University Press. Kindle Edition

4.    https://www.sciencedirect.com/science/article/abs/pii/S1053811905000819

5.    https://www.frontiersin.org/journals/psychology/articles/10.3389/fpsyg.2023.1217288/full

6.    https://www.frontiersin.org/journals/psychology/articles/10.3389/fpsyg.2023.1217288/full

7.    https://pmc.ncbi.nlm.nih.gov/articles/PMC11595727/

8.    https://www.sciencedirect.com/science/article/abs/pii/S1053811905000819

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10.  https://pmc.ncbi.nlm.nih.gov/articles/PMC2770698/

11.  https://pmc.ncbi.nlm.nih.gov/articles/PMC2770698/

12.  https://pmc.ncbi.nlm.nih.gov/articles/PMC5754247/

13.  https://pmc.ncbi.nlm.nih.gov/articles/PMC4270739/

14.  https://pmc.ncbi.nlm.nih.gov/articles/PMC5479093/

15.  https://pmc.ncbi.nlm.nih.gov/articles/PMC8839299/

16.  https://www.sciencedirect.com/science/article/abs/pii/S0160289621000817

17. “Family Structure and Stability Effects on Child Cognitive Performance”. Terry-Ann Craigie Center for Research on Child Wellbeing Office of Population Research Princeton University December 31, 2009

18. https://www.scientificamerican.com/article/silicon-valley-is-reviving-the-discredited-and-discriminatory-idea-of-race/

19.  https://pmc.ncbi.nlm.nih.gov/articles/PMC3704307/

20.  https://pmc.ncbi.nlm.nih.gov/articles/PMC4354297/#sec11