Psychologists agree that intelligence differs among populations but disagree as to why this phenomenon exists.
Review the state of research examining the causes of group differences in intelligence and the effect of stereotype threat on performance
Psychologists widely believe that human groups differ in their respective levels of general intelligence. While this highly controversial study has proven reliable and valid, it has not adequately answered the question of why these differences exist.
Scientists are certain that both genetics and the environment have a role in the discrepancies among human populations and their levels of intelligence. These two factors work together to influence group differences.
In general, in the United States, race is the most commonly studied, socially-constructed group division. Raw scores among races have both risen and converged over the last 40 years of study.
Socioeconomics (access to education), test bias (issues in constructing IQ tests), and stereotype threat (self-fulfilling prophecy of test scores) are all environmental influences on group differences in intelligence.
the experience of anxiety or concern in a situation where a person has the potential to confirm a negative stereotype about his social group
The variance of intelligence scores among individual human beings can be extrapolated to larger population differences in general intelligence and mental capacity. The study of group differences in intelligence is very controversial as it attempts to separate and rank human groups based on divisive social constructs such as race, ethnicity, and gender. Although psychologists generally agree that discrepancies among group intelligence levels do exist, many continue to debate the actual causes of these differences.
From the beginning of intellectual research, psychologists have attempted to rank individuals and populations on their respective intelligence scores. Claims of racial and sexual differences were used to justify practices such as slavery and misogyny. Before IQ testing was developed, scientists used to rely on crude data such as head or brain size or reaction times to estimate intelligence levels. Thus, women who are biologically smaller than men, or children who are categorically less adept than adults, were inaccurately thought to be less intelligent on average. It was not until Alfred Binet and the emergence of the IQ test that psychologists were able to collect data that could accurately and reliably compare human groups .
Since the advent of reliable and valid IQ testing methods, psychologists have demonstrated, and the APA has declared, that differences in group intelligence are undeniable. Intelligence researchers Hunt and Carlson outline four major points concerning the status of this field of study which succinctly summarize much of the controversy and question involved. First, it is clear that the current state of research reflects real differences in average group intelligence which is caused by a combination of genetics and the environment. Second, these differences in average cognitive ability between groups such as races are caused almost entirely by social and environmental factors. Third, while the data clearly shows differences in test scores, it remains possible that the test takers were the victims of inherent bias and thus no difference actually exists. Fourth, both ‘race' and ‘intelligence' are human-conceived social constructs which would render any scientific finding using them less meaningful.
The greatest amount of research involving group differences in intelligence has been focused on different racial groups. Gender differences have been of historical importance, but modern testing has been constructed such that there should be no discrepancies between the average score of a man or woman. In general, studies in the United States have ranked racial group score data from highest to lowest intelligence with Asian Americans at the top, White Americans in the middle, and African Americas at the bottom. These findings, while statistically significant and frequently repeated, do not account for causation into the discrepancies themselves. There is also the question as to whether every sample taken in the United States is representative of the whole variance of cultural norms within a given group.
During the early years of research, raw scores on IQ tests systematically rose throughout the world. This increase is now called the "Flynn effect," named after Jim Flynn who did much of the work to document and promote awareness of this phenomenon and its implications. Recent meta-analysis has concluded that the Flynn effect and the closing gap in group differences in intelligence have different origins. Scientists argue that the environmental factors which are thought to have caused the Flynn effect are unlikely to be the same factors at work in group discrepancies.
Potential environmental causes of differences in group intelligence levels vary greatly and are further complicated by the relationship that external factors have with internal genetics. These factors are not mutually exclusive and often work together to influence a group's intelligence. Potential causes include socioeconomics, test bias, and stereotype threat.
Socioeconomics is purely a term for prevalence, access, and availability of education and learning environments. Not everyone in the United States, or the world for that matter, is given the same opportunities when it comes to developing intelligence. Test bias refers to the construct of the test itself as it is applied to different populations. It is possible that the very composition of certain IQ tests can allow or inhibit certain levels of performance among different groups. Stereotype threat is the fear that a person's behavior will naturally and unconsciously conform to the stereotypes that define that person's group. Testing situations that highlight the fact that intelligence is being calculated have been shown to lower scores in groups of people that associate themselves with the stereotype of a lower IQ group. Once again, none of these factors determines intelligence alone. Instead, all of them work simultaneously to help determine a group's intelligence.