An intelligence quotient (IQ) is a total score derived from a set of standardised tests or subtests designed to assess human intelligence. The abbreviation "IQ" was coined by the psychologist William Stern for the German term Intelligenzquotient,his term for a scoring method for intelligence tests at University of Breslau he advocated in a 1912 book.
Discussions of race and intelligence –specifically,claims of differences in intelligence along racial lines –have appeared in both popular science and academic research since the modern concept of race was first introduced. With the inception of IQ testing in the early 20th century,differences in average test performance between racial groups were observed,though these differences have fluctuated and in many cases steadily decreased over time. Complicating the issue,modern science has shown race to be a socially constructed phenomenon rather than a biological reality,and there are various conflicting definitions of intelligence. In particular,the validity of IQ testing as a metric for human intelligence is disputed. Today,the scientific consensus is that genetics does not explain differences in IQ test performance between groups,and that observed differences are environmental in origin.
The Bell Curve:Intelligence and Class Structure in American Life is a 1994 book by psychologist Richard J. Herrnstein and political scientist Charles Murray,in which the authors argue that human intelligence is substantially influenced by both inherited and environmental factors and that it is a better predictor of many personal outcomes,including financial income,job performance,birth out of wedlock,and involvement in crime than are an individual's parental socioeconomic status. They also argue that those with high intelligence,the "cognitive elite",are becoming separated from those of average and below-average intelligence,and that this separation is a source of social division within the United States.
Nature versus nurture is a long-standing debate in biology and society about the relative influence on human beings of their genetic inheritance (nature) and the environmental conditions of their development (nurture). The alliterative expression "nature and nurture" in English has been in use since at least the Elizabethan period and goes back to medieval French. The complementary combination of the two concepts is an ancient concept. Nature is what people think of as pre-wiring and is influenced by genetic inheritance and other biological factors. Nurture is generally taken as the influence of external factors after conception e.g. the product of exposure,experience and learning on an individual.
Heritability is a statistic used in the fields of breeding and genetics that estimates the degree of variation in a phenotypic trait in a population that is due to genetic variation between individuals in that population. The concept of heritability can be expressed in the form of the following question:"What is the proportion of the variation in a given trait within a population that is not explained by the environment or random chance?"
Twin studies are studies conducted on identical or fraternal twins. They aim to reveal the importance of environmental and genetic influences for traits,phenotypes,and disorders. Twin research is considered a key tool in behavioral genetics and in related fields,from biology to psychology. Twin studies are part of the broader methodology used in behavior genetics,which uses all data that are genetically informative –siblings studies,adoption studies,pedigree,etc. These studies have been used to track traits ranging from personal behavior to the presentation of severe mental illnesses such as schizophrenia.
The g factor is a construct developed in psychometric investigations of cognitive abilities and human intelligence. It is a variable that summarizes positive correlations among different cognitive tasks,reflecting the fact that an individual's performance on one type of cognitive task tends to be comparable to that person's performance on other kinds of cognitive tasks. The g factor typically accounts for 40 to 50 percent of the between-individual performance differences on a given cognitive test,and composite scores based on many tests are frequently regarded as estimates of individuals' standing on the g factor. The terms IQ,general intelligence,general cognitive ability,general mental ability,and simply intelligence are often used interchangeably to refer to this common core shared by cognitive tests. However,the g factor itself is a mathematical construct indicating the level of observed correlation between cognitive tasks. The measured value of this construct depends on the cognitive tasks that are used,and little is known about the underlying causes of the observed correlations.
Hereditarianism is the doctrine or school of thought that heredity plays a significant role in determining human nature and character traits,such as intelligence and personality. Hereditarians believe in the power of genetics to explain human character traits and solve human social and political problems. Hereditarians adopt the view that an understanding of human evolution can extend the understanding of human nature.
Research on the heritability of IQ inquires into the degree of variation in IQ within a population that is due to genetic variation between individuals in that population. There has been significant controversy in the academic community about the heritability of IQ since research on the issue began in the late nineteenth century. Intelligence in the normal range is a polygenic trait,meaning that it is influenced by more than one gene,and in the case of intelligence at least 500 genes. Further,explaining the similarity in IQ of closely related persons requires careful study because environmental factors may be correlated with genetic factors.
"Mainstream Science on Intelligence" was a public statement issued by a group of researchers led by psychologist Linda Gottfredson. It was published originally in The Wall Street Journal on December 13,1994,as a response to criticism of the book The Bell Curve by Richard Herrnstein and Charles Murray,which appeared earlier the same year. The statement defended Herrnstein and Murray's controversial claims about race and intelligence,including the claim that average intelligence quotient (IQ) differences between racial and ethnic groups may be at least partly genetic in origin. This view is now considered discredited by mainstream science.
Robert Joseph Plomin is an American/British psychologist and geneticist best known for his work in twin studies and behavior genetics. A Review of General Psychology survey,published in 2002,ranked Plomin as the 71st most cited psychologist of the 20th century. He is the author of several books on genetics and psychology.
The IQ Controversy,the Media and Public Policy is a book published by Smith College professor emeritus Stanley Rothman and Harvard researcher Mark Snyderman in 1988. Claiming to document liberal bias in media coverage of scientific findings regarding intelligence quotient (IQ),the book builds on a survey of the opinions of hundreds of North American psychologists,sociologists and educationalists conducted by the authors in 1984. The book also includes an analysis of the reporting on intelligence testing by the press and television in the US for the period 1969–1983,as well as an opinion poll of 207 journalists and 86 science editors about IQ testing.
James Jay Joseph is an American clinical psychologist and author. He practices psychology in the San Francisco Bay Area. He is known for his criticisms of behavior genetics and twin studies in psychology and psychiatry. His view,as he articulated in his 2003 book The Gene Illusion,is that such research is so flawed as to render all of its results completely meaningless.
Irving Isadore Gottesman was an American professor of psychology who devoted most of his career to the study of the genetics of schizophrenia. He wrote 17 books and more than 290 other publications,mostly on schizophrenia and behavioral genetics,and created the first academic program on behavioral genetics in the United States. He won awards such as the Hofheimer Prize for Research,the highest award from the American Psychiatric Association for psychiatric research. Lastly,Gottesman was a professor in the psychology department at the University of Minnesota,where he received his Ph.D.
Behavioural genetics,also referred to as behaviour genetics,is a field of scientific research that uses genetic methods to investigate the nature and origins of individual differences in behaviour. While the name "behavioural genetics" connotes a focus on genetic influences,the field broadly investigates the extent to which genetic and environmental factors influence individual differences,and the development of research designs that can remove the confounding of genes and environment. Behavioural genetics was founded as a scientific discipline by Francis Galton in the late 19th century,only to be discredited through association with eugenics movements before and during World War II. In the latter half of the 20th century,the field saw renewed prominence with research on inheritance of behaviour and mental illness in humans,as well as research on genetically informative model organisms through selective breeding and crosses. In the late 20th and early 21st centuries,technological advances in molecular genetics made it possible to measure and modify the genome directly. This led to major advances in model organism research and in human studies,leading to new scientific discoveries.
The following outline is provided as an overview of and topical guide to human intelligence:
Sex differences in human intelligence have long been a topic of debate among researchers and scholars. It is now recognized that there are no significant sex differences in general intelligence,though particular subtypes of intelligence vary somewhat between sexes.
Jensenism is a term coined by New York Times writer Lee Edson. Named after educational psychologist Arthur Jensen,it was originally defined as "the theory that IQ is largely determined by the genes". The term was coined after Jensen published the article "How Much Can We Boost IQ and Scholastic Achievement?" in the Harvard Educational Review in 1969. It has since been included in several dictionaries.
Kathryn Paige Harden is an American psychologist and behavior geneticist. She is Professor of Psychology at the University of Texas at Austin,where she is also the leader of the Developmental Behavior Genetics lab and the co-director of the Texas Twin Project. She is also a Faculty Research Associate at the University of Texas at Austin's Population Research Center and a Jacobs Foundation research fellow.
In behavioral genetics,the Scarr–Rowe effect,also known as the Scarr–Rowe hypothesis,refers to the proposed moderating effect of low socioeconomic status on the heritability of children's IQ. According to this hypothesis,lower socioeconomic status and greater exposure to social disadvantage during childhood leads to a decrease in the heritability of IQ,as compared to children raised in more advantaged environments. It is considered an example of gene–environment interaction. This hypothesized effect was first proposed by Sandra Scarr,who found support for it in a 1971 study of twins in Philadelphia,and these results were replicated by David C. Rowe in 1999. Since then,similar results have been replicated numerous times,though not all replication studies have yielded positive results. A 2015 meta-analysis found that the effect was predominant in the United States while less evident in societies with robust child welfare systems.
