ABSTRACT
Differences in the biological intelligence can be measured by means of Intelligence quotient (IQ) tests, but only indirectly, and with an admixture of inputs from many environmental sources—socioeconomic status, education, family upbringing, cultural factors, and so on. Although Francis Galton suggested reaction time and similar tests as biological measures of brain functioning, they are obviously just a halfway house in that direction. What he had in mind did not then exist, namely electronic ways and means of investigating directly what was going on in the brain, such as the electroencephalograph, the positron emission tomography scan, or the magnetic resonance imaging technique. Clearly, the social or practical intelligence is too complex a concept to be of any scientific value; science relies on the reduction of complex concepts to simpler, more elementary ones. There are some biological correlates of IQ that are fairly obvious, although they have given rise to a great deal of controversy.
