The issue of what causes individual differences in intelligence goes beyond psychology, and involves moral, political, ethical, educational, social, physiological and statistical issues to name just a few. The issue of how differences in intelligence come about between individuals and groups is a topic of much fascination and controversy - it can arouse strong reactions and elicit personal beliefs and biases.
This page outlines some of the main psychological concepts and evidence that relates to explaining individual differences in intelligence.
As a student, it is your responsibility to develop a familiarity with the basic arguments, strengths, and weaknesses for and against the causal influences and correlates of intelligence. Nature vs Nurture - What do you think?
In looking for the causes of individual differences in intelligence, a major issue is the relative contribution of genetics and environment.
The zeitgeist (the intellectual and culture "flavor" of a time and place) has swung back and forth over time with regard to the amount of influence that nature vs. nature has on human intelligence.
For example, in the late 1800's in the UK, as Darwinism took off, the role of genetically determined capability was considered very important.
This was in constrast, for example, to the 1960's in the USA, when views were more in favor a "tabula rasa" (blank state) view of human intelligence - in other words, all people are capable of much more, if given conducive environmental conditions in which to reach their potential
Currently the Zeitgeist is the Western psychological world is somewhere inbetween - both genetics and environment are seen as playing important roles. To be more precise, the modern view about nature vs nurture in intelligence is "interactionist". This view is well expressed by Ridley (1999, p.77):
"Mother Nature has plainly not entrusted the determination of our intellectual capacities to the blind fate of a gene or genes; she gave us parents, learning, language, culture and education to program ourselves with."
Historical trends in the nature-nurture debate
Late 19th century - early 20th century (Nature)
From the mid to late 1800's through to the early 1900's opinions rested in the nature camp. This was consistent with the scientific discoveries of the role of inheritance and natural selection by Mendel and Darwin.
The major contributor to the psychological argument was Francis Galton in his book "Hereditary Genius: Its Laws and Consequences� (1869).
Galton had observed that the gifted individuals tended to come from families which had other gifted individuals. He went on to analyze biographical dictionaries and encyclopedias, and became convinced that talent in science, the professions, and the arts, ran in families.
Galton took this observation one step further, to argue that it would be "quite practicable to produce a high gifted race of men by judicious marriages during several consecutive generations".
This suggestion became know as eugenics, "the study of the agencies under social control that may improve or repair the racial qualities of future generations, either physically or mentally." Galton wanted to speed up the process of natural selection, stating that: "What Nature does blindly, slowly, and ruthlessly, man may do providently, quickly, and kindly�.
Galton was convinced that "intelligence must be bred, not trained". Such arguments have had massive social consequences and have been used to support apartheid policies, sterilization programs, and other acts of withholding basic human rights from minority groups.
Post WWI: 1920�s-1930�s
After World War I, careful reanalysis of the mass of intelligence test data took place. This began to challenge the commonly held view that intelligence was directly, genetically linked to racial differences:
e.g. blacks from Illinois had higher IQ scores than...