What's intelligence?

not just capability for such and such..

Descartes (1596-1650) responding to Montaigne's "Essays" on abilities of animals, argues that automatic ability in animals does not show reason; instead it shows none!

"nature makes them behave as they do according to the disposition of their organs; just as a clock, composed only of wheels and weights and springs can count the hours and measure the time more accurately than we can with all our intelligence. Descartes, R. (1641) Discourse on Methods, Fifth Part.

While Descartes' argument comes out of a cultural, scientific, linguistic, and religious environment quite remote from our own, it provides a high contrast background against which to evaluate human and animal abilities.

Intelligence is a general adaptive capacity enablling flexible responses of individuals to changing environments

This suggests that we cannot assess the "intelligence" of an organism by observing it in its natural environment for which we suppose it is already well-adapted. The question is whether or how much of this adaptation is due to the "intelligence" of the individual rather than inheritance from its ancestors (ontogeny vs phylogeny, nurture vs nature)

We can only evaluate this by evaluating individual organism's ability to adapt to novel environments, either experimentally, natural observation, or pure speculation!

Even this is not straightforward since a complex adaptive behavior may have components of different origins --even in members of the same species. (Human language may be an example of this, especially comparing early vs. later acquisition. See language notes.)

Finally, even this definition ignores the problems of specifying WHAT environments should be considered.

intelligence is related to LACK of specialization

This of course is consistent with the extreme neotenous condition of humans. Recall our discussion of the ontogeny of forelimbs-- also very unspecialized.

and a relatively large, multipurpose brain

intermediate views

Intelligence results from a set of abilities, including multipurpose flexibility but also specific language skills, spatial and other representational ability, memory capacities, motor skills, social skills, etc. that indeed are inherited to some extent.

Can we do without a concept of intelligence?

Apparently some behaviorist psychologists thought so in that they believed the general principles of behavior could be discovered using almost any species and that the only differences were in sensory-motor processes and perhaps size of memory. Although much of what they had to say about behavior in general seems now misguided, there is the strong possibility that we shall find that the idea of "intelligence" is an intuitive concept better understood in terms of differential component processes including sensori-motor and memory processes, processing rates, motivation, and the self-organizing characteristics of the brain as it develops in particular environments.

For now, it seems reasonable to take "intelligence" as characterized above.

Why big brains?

or first--why brains at all?

I suppose we should evaluate the role of the brain itself in intelligent behavior. Passingham (1980) reviews the role of naturally occurring lesions and experimentally lesioned animals in understanding the role of various brain regions in behavior. Intact mammal brains are required for intelligent behavior (However Karl Lashley (1929?) demonstrated animal brains could sustain a surprising amount of damage and maintain performance and there are a few amazing clinical cases of humans with serious brain tissue deficit maintaining near normal intellectual functioning.)

lesion studies (see HP for details)

One implication of these findings is that motivation, interest and planning play a large role in adaptive behavior. Clinically, the famous case of Phineas Gage (MacLean, 1990) who had an iron bar pass through his left frontal cortex from below his eye and exiting through his skull demonstrated how planning and interests in the future depend on forebrain structure. Gage was a conscientious railway construction foreman until the accident; afterward he became an "indulgent, profane, capricious, vacillating" person who drifted from job to job until he died. It appeared that the frontal lobes damaged in Gage play a major role in control of temperament, social interactions, and planning. In the words of his physician, "Gage was no longer Gage." (MacLean (1990).

This was experimentally demonstrated in chimpanzees, research which led to the use of pre-frontal lobotomy in the 1940-1960s as a psychiatric treatment for serious anxiety or other? disorders.

Is there evidence for greater intelligence in big brains?

There remains much controversy about this issue--see Gould, 1981, Mismeasure of Man). However, even Darwin believed it was important, noting for example that more intelligent insects had larger ganglia and that domestic animals had smaller brains than their wild counterparts. Taken together, this suggests that intelligence may in part depend on brain size but that size itself needs analysis and can reflect environmental circumstances.

between species?

Harry Harlow (190x-198x) pioneered methods of evaluating "learning set" ability across species using his Wisconsin General Testing Apparatus (WGTA).

Passingham (1982) summarizes much of the research in the figure below, showing performance of various species on a two-choice visual discrimination task in which the organism picks one of two objects with a hidden reward under it. Essentially the subject must learn a rule --that the food is under a certain type of object despite other changes in position or features of the objects--and follow that rule in choosing.

Sketched from Fig. 5.8 in Passingham (1980).

Passingham concludes from these data that when mammals are ranked in terms of their improvement over a series of these problems, their rank is predicted by Jerison's (1973) measure of surplus brain cells.

within species

One can safely assume that except for the most fundamental aspects of individuals--number of limbs, etc., there will be variation on every characteristic including "intelligence." Of course the details will depend on how it is assessed. Moreover if it is a complex of other factors working synergistically, then measurement will even be more problematical and variation likely to be greater.

Passingham is very cautious in assessing the data available to him and concludes the relationship between brain size and intelligence is very slight at best. Nevertheless, only a slight advantage (correlation) may have considerable evolutionary significance in explaining the rapid increase in hominid brains over the past 2-3 million years.

Greater intelligence would be particular important in this period of considerable climatic variation --variation that would place a premium on intelligence. (See Calvin's paper on intelligence.)

"When we say intelligent rather than clever we are often implying a substantial amount of looking ahead. " Calvin p.23

recent data on brain size & intelligence

A recent review by Wickett, et al. (1995?) reports that most correlations based on head size range between r = .10 to r = .30, with an n-weighted mean of r = .194.

Using new methods, four recent studies of this relationship for the first time obtained estimates of brain size from high quality magnetic resonance imaging (MRI), instead of using external cranial dimensions. All four studies show about twice the correlation with intelligence than does head size. Willerman et al. (1991) report an estimated correlation of r = .35 (N = 40); Andreasen et al. (1993) found a correlation of r= .38 (N = 67); Raz et al (in press) found a correlation of r = .43 (N = 29); and Wickett et al. (in press) report a correlation of r = .395 (N = 40, all females). These are all statistically significant.

It appears that there is a small but reliable relationship between intelligence and brain size. This small difference has no importance in assessing individual intelligence --considering all the other factors involved. It does have evolutionary significance since a very small fitness advantage of a characteristic can, over generations, can have a dramatic effect --like the tripling of the hominid brain over the last 2 million years.

Hamilton (1935) reported that rats selected for 12 generations to be either "maze-bright" or "maze-dull" differed by about 2.5 standard deviations in brain weight. Within unselected control rats there was a correlation of r = .25 between maze ability and brain weight. Recently Anderson (1993) reported data on rats in which several cognitive tasks were given and a general factor extracted, and brain weights were obtained. The correlation between this general factor and brain weights in these rats was r = .48.

These animals studies only support the general idea that brain size is related to certain abilities. However keep in mind what Darwin observed, that the early experiences themselves can influence brain size. Indeed, it is conceivable that some increments in brain size occur from the extra post-natal experience and nutrition that the "premature" human brain gets as an indirect consequence of its neotenous condition.

big bodies more efficient in flush environments?

lower "overhead" costs for surplus neurons in big brains?

other advantages of big brains

larger less densely packed neurons

This allows greater interconnectivity among individual neurons.

greater blood supply and support cells

glial cell numbers increase as brains get large

These cells essentially take up the space among neurons, having served to guide the placement of neurons during early development. here is an increasing glial/neuron ratio as brain weight increases.
Einstein's brain!
Post mortem analysis of Einstein's brain by Schiebel (19xx, video) reportedly indicates an usually large number of glial cells!

other aspects of brain function and intelligent behavior

motivation, interests, curiosity

effects of prefrontal lesions on motivation

Passingham notes that relative brain size predicts well the responsiveness ("curiosity") of zoo animals to novel objects over time. Suppose animals just get bored after exhausting their repertoire of responses to the object. Perhaps brain size indirectly reflects the variety of responses available to various species. Primates have the obvious handling advantage over carnivores, for example. And humans have a linguistic repertoire far exceeding that of any other primate.

Responsive of zoo animals to novel objects

Sketched after Fig. 5.10, Passingham (1980)

social skills

Humphries (1976) suggested human intelligence may have come from the large brain needed to engage in complex social relationships. Support for this comes from a study by Dunbar (199x) showing that typical group size is perhaps the best predictor of brain size in primates.

foraging and nutrition

Obtaining food plays a double role.

In phylogeny of a species, it drives evolution of the necessary mental capacities for obtaining food as well as in ontogeny of an individual, nutrition plays a complex role in maximizing the intelligence of the organism. (See diagram below adapted from Brown and Pollitt (1996) on the complex effects of malnutrition.)

Adequate nutrition is also fundamental to fertility thus linking foraging to the spread of "intelligence" in the population.

imitation skills

The important point here is that there are a number of reasons to suppose social animals would be more intelligent. However not all of these involve imitation which seems to be quite rare in animals and even large primates. Other social factors, e.g stimulus or response enhancement, rather than imitation are much more common. Imitation requires complex sensorimotor and cognitive processes along with the social dimension. (See Bryne notes and book and Tomasello, 1990, for details)

language and culture

Like imitation, these play a role in accumulated wisdom --the acquisition of acquired traits and knowledge without going through heredity.

domain-specific intelligence

Organisms may be very skillful in dealing with specific objects or situations but not be able to generalize those skills to other situations. This raises questions about the very nature of intelligence. Many humans, for example, can solve a certain logical problem with some variables but not others--even though the logic of the problem is identical. (cf. Rumbaugh, 1988, Cheney-Seyfarth, 1990: Cosmides, 1989)

Heredity, genes. and intelligence

Much of the political and social concern about intelligence in humans revolves around concerns of differences among various ethnic or racial groups of humans. Reading statements from the 19th century by Galton and especially Spencer and then seeing how these ideas were transformed into the political horrors of Nazi Germany explains much of the disfavor the idea of hereditary intelligence engenders. (The Soviet Union banned the use of such tests along with most of the field of genetics from about 1920 until the 1950s.)

In the United States, testing was connected with the rise of eugenics ("good genes") movement that advocated sterilization for mentally retarded and convicted criminals.

a brief outline of the measurement of intelligence

Some early efforts involved measuring brain size; Francis Galton unsuccessfully tried to use sensorimotor measures (e.g. reaction times) to predict success in life --presumably reflecting increased adaptive capabilities. The general idea is to establish a metric for assessing an organism's adaptibility (i. e. intelligence) and show that it predicts some real-life "adaptability."

Binet in the early 1900s in France developed a test to evaluate children's potential for schooling. It assessed the basic skills of children that schoolteachers believed necessary for further learning. Basic number skills, language abilities, and logical assessment were prominent. From this developed the idea of group tests, norms, and mental age. Piaget, trained as a biologist, worked in Binet's lab and began to apply his ideas on biological epistemology (growth of knowledge) to humans.

Many in England, e.g. Spearman, Fisher, worked on the mathematical development of testing that we have today. Spearman was responsible for the idea of general intelligence as a "common factor--g--" to all performance--not seen directly but revealed in all adaptive behavior. The technique of "factor analysis" was devised to extract the common "factor" in a range of tests. Some speculated "g" reflected some general brain capacity such as size or speed.

In the USA, Binet's test was translated and revised for use here by psychologists at Stanford--resulting in the widely used Stanford-Binet test by L. Terman. R. M. Yerkes and other also devised a version of the Binet, "A Point Scale for Measuring Mental Ability, 1916" These tests were used in mobilzation for WWI--with minimal success. Nevertheless, they became important factors in clinical, school, and industrial settings.

While scores on these tests may predict success in schools, many critics point out that language skills and cultural biases make inferences about heredity on the basis of these tests very risky.

famous figures.

Francis Galton (18xx-1911)

Galton was a cousin of Charles Darwin and was one of the first to attempt measurement of intelligence; he was also a founder of the widespread eugenics movement to improve the human race. By 1931, thirty states in the US had passed sterilization laws.

"I propose to show in this book that a man's natural abilities are derived by inheritance, under exactly the same limitations as are the form and physical features of the whole organic world. Consequently, as it is is easy, notwithstanding those limitations, to obtain by careful selection a permanent breed of dogs or horses gifted with peculiar powers of running, or doing anything else, so it would be quite practicable to produce a highly gifted race of men by judicious marriages during several consecutive marriages."

Galton, F. (1869). Hereditary genius, an inquiry into its laws and consequences .

James Mark Baldwin (1861-1934)

(See Chevalier-Skolnikoff, S. (1977). A Piagetian model for describing and comparing socialization in monkey, ape, and human infants. [136-166] )

Terman (developed the Stanford-Binet)

the complex relationship between genes and behavior

We saw how complex and indirect the relationship between nutrition and intelligence can be. The relationship between genes and intelligence must be more so. Genes determine enzymes that regulate and structure biological development; at every stage, one's environment plays an important, necessary role. See the table below outlining these processes.
PROCESSES                  PRODUCTS                   ENVIRONMENTAL              
form genotype at           regulatory genes           amino acids, etc.          
conception                 structural genes                                      
enzyme production          enyzmes                    nutrients (proteins,       
                                                      carbohydrates, fats...)    

regulated biochemical      cell development and       nutrients including        
reactions                  metabolism                 oxygen etc prenatally      
                                                      via the placenta (etc      
                                                      here can have negative     
                                                      effects, e.g. viruses,     
                                                      inadequate oxygen,         
                                                      hormone-like chemicals)    

organized development of   physiological structures   nutrients and              
body incl. c.n.s.,         including neural           sensory-motor feedback     
endocrine systems, etc.    circuits and sense         effects on neural          
                           receptors                  development esp. late      
                                                      fetal and early neonatal   

c.n.s commands, sensory    Behavior                   sensory input nutrients    

some tentative conclusions

Most IQ tests evaluate a narrow range of abilities that are influenced by a complex of biological and environmental factors. Even if there are small differences attributable specifically to gene differences, these are not large relative to environmental factors and never are independent of them. They seem irrelevant to comparisons among primate species and add little to our understanding human nature beyond the assumption that variablity must have existed in order for natural selection to function.

What are characteristics of "intelligent" creatures?

Data from Gould (1977), Passingham (1980) and reflection suggest a complex of interrelated characteristics are observed in intelligent creatures. Many of these derive from the neotenous condition of primates but can be expected to reflect "intelligence" in other species who happen to have similar characteristics.

large brain and "surplus" neurons
long life
high manipulative ability

dexterity in hand, paw, claw, bill, trunk, tentacle, and vocal tract

The puppetmeister metaphor is useful here; how may strings and how often must you pull them gives a rough indication of the sophistication of the system. Generally speaking, more degrees of freedom require greater information flow per unit time.

The most complex example is probably speech, where Darley, F. L., Aronson, A. E., & Brown, J. R. (1975). Motor speech disorders . Philadelphia: Saunders estimate 14,000 muscles must be controlled and at a very rapid rate!

small numberof offspring (reproductive strategy)
long period of immaturity and degree of immaturity at birth
complex vocal communication
complex social organization
high parental investment
high visual acuity

Vision requires a sophisticated nervous system that can be used for "intelligent" actions--vision thus is perhaps a useful preadaption for intelligence. It may be particularly important enabling the use of visual imagery in problem solving. See Piaget's "figurative intelligence" and Kohler's "insight", etc.

Tentative final comments

The outline of primate intelligence that Passingham (1980) sketched remains reasonably accurate today, although Bryne (1995) points out some limitations. There is additional evidence on the small relationship between brain size and intelligence; there is also much more evidence on social factors in intelligence. Finally, while there is much more information about the role of genes in behavior, none of these relationships appears at all direct nor independent of many aspects of an individual's environment.

Thus brain size may be a function of specific regulatory genes, it is also a function of nutrition and experience -especially early experiences. Natural selection can operate directly only on the regulatory gene component of the phenotype brain, though other genes relating to parenting and accelerated gestation--relevant to nutrition and neonatal experiences-- may also be enhanced.

(Recall the sketch on multiple effects of genes on the phenotype in my evolution notes. Plug the above variables into that sketch. You also might want to read Calvin's recent Scientific American article (Oct., 1994) on "The emergence of intelligence.")