1. Those I have referred to as IQ-ists believe that IQ, representing an individual's overall score on a battery of verbal reasoning tests, number puzzles, and pattern matching tasks, measures a unitary property of the central nervous system, which is identified as intelligence.
2. To the IQ-ist, the unitary nature of intelligence is established by the correlations between scores on the various puzzles comprising the IQ test. A mathematical construct named g, the exact nature of which probably very few people understand, represents the degree of correlation among tests, and effectively conceals the rather limited degree of correlation that is actually observed, i.e., r-squared values less than 0.5.
Note that the mean correlation coefficient, r, is quite low, around 0.3, which means that, on average, variation in any one factor explains less than 10% (r2) of the variation in another factor, meaning that mental abilities are largely independent of one another. Or put another way, it is possible, and in fact quite normal, to be smart at one thing and dumb at another. Image source. Click image to enlarge.
3. A biologist will generally understand the term intelligence more broadly than the IQ-ist, and in a Darwinian sense. Thus they will usually include within the meaning of the term all cognitive activity that promotes the survival and reproductive success of the organism.
In this respect, the Darwinian view is much closer to the commonsense understanding of intelligence, which the Merriam-Webster dictionary defines as:
the ability to learn or understand or to deal with new or trying situations ... the ability to apply knowledge to manipulate one's environment or to think abstractly ...4. To the Darwinian, the skills required to perform well on an IQ test are extremely limited in range. They demonstrate the capacity to read with comprehension, write with clarity and add up, which are certainly adaptive for those who seek to ensure that there is food in the refrigerator by working at the Post Office or in some other clerical, bureaucratic, or middle-management job.
In the jungle-dweller or the hunter-gatherer, however, the Darwinist would recognise intelligence in very different skills, including the ability to interpret the sights, and sounds, and smells of both predators and prey; to distinguish the poisonous mushroom among a thousand that are edible; to step from boulder to boulder across a creek in spate when one misstep could mean instant death; to cast a spear or shoot an arrow that saps the strength of an enraged bear, or a charging buffalo.
5. In addition, the Darwinist will recognize as manifestations of intelligence a multitude of skills that the IQ-ist ignores but which are essential to the survival of mankind both primitive and modern: the ability to charm a maid or beguile a swain; the power to lead in battle, or sway the election crowd; the Machiavellian gift of manipulation; the ability to entertain; the power of technical innovation.
6. Defined as the Darwinist sees it, the notion of intelligence as a unitary property of the central nervous system is untenable. The nerd who designs the combat aircraft is unlikely to have the coordination to fly it; the charismatic politician may be devoid of understanding in matters of economics, education, or military strategy; the pop singer who can fill a stadium, may be a political imbecile.
7. The neurologist, examining the substrate of the cognitive activity underlying intelligent behavior sees the visual, olfactory, auditory, computational and other aspects of information processing occurring in separate specialized parts of the brain. To the neurologist, therefore, it is evident that aptitudes may vary according to the size, structure, and physiological properties of the various neural components of the brain that are involved. Thus the Australian aboriginal's path-finding skill appears related to exceptional development of the visual cortex. Carl Gauss's extraordinary mathematical gifts may have been due to the exceptional convolutions of his cerebral cortex, as observed at autopsy.
8. In summary, the IQ-ists view of intelligence is valid only on the IQ-ist's peculiar and tautological definitions of IQ and intelligence, viz: IQ = intelligence, and intelligence = IQ.
And even then the definition of intelligence is weak, since it ignores the fact that scores on the components of the IQ test are not tightly correlated, which means that the math geek may have poor linguistic skills, with the result that their IQ reflects neither their mathematical competence nor their linguistic incompetence. Likewise, a literary genius with poor pattern-matching ability would have an IQ reflecting neither their gift nor their weakness.
9. My conclusion is that if psychology is to advance in the field of intelligence assessment, it must greatly broaden the definition of intelligence and recognize the modularity of both the brain and its properties as manifest in intelligent behavior.
10. In addition, there is the question of environmental effects — education, culture, nutrition, disease — on intelligence, which is critical to the assessment of the intellectual potential of particular racial or social groups. The Flynn effect, that for a hundred years has added 3 to 5 IQ points every decade to average IQ scores of Western nations makes clear that IQ test results are heavily influenced by environmental factors, though what the key factors are, whether cultural, dietary, or disease-related remains to be determined.