Race and intelligence
Complicating the issue, modern science has concluded that race is a socially constructed phenomenon rather than a biological reality, and there exist various conflicting definitions of intelligence.
However, other studies soon appeared, contesting these conclusions and arguing that the Army tests had not adequately controlled for environmental factors, such as socioeconomic and educational inequality between the groups.
Later observations of phenomena such as the Flynn effect and disparities in access to prenatal care highlighted ways in which environmental factors affect group IQ differences.
In recent decades, as understanding of human genetics has advanced, claims of inherent differences in intelligence between races have been broadly rejected by scientists on both theoretical and empirical grounds.
[8] The results were widely publicized by a lobby of anti-immigration activists, including the conservationist and theorist of scientific racism Madison Grant, who considered the so-called Nordic race to be superior, but under threat because of immigration by "inferior breeds."
[11] Discussions of the issue in the United States, especially in the writings of Madison Grant, influenced German Nazi claims that the "Nordics" were a "master race.
[19][20] Another revival of public debate followed the appearance of The Bell Curve (1994), a book by Richard Herrnstein and Charles Murray that supported the general viewpoint of Jensen.
[15][22][24][25][26] Arthur Jensen, who jointly with Rushton published a 2005 review article arguing that the difference in average IQs between blacks and whites is partly due to genetics, received $1.1 million in grants from the Pioneer Fund.
[27][28] According to Ashley Montagu, "The University of California's Arthur Jensen, cited twenty-three times in The Bell Curve's bibliography, is the book's principal authority on the intellectual inferiority of blacks.
[35] Correlations between scores on various types of IQ tests led English psychologist Charles Spearman to propose in 1904 the existence of an underlying factor, which he referred to as "g" or "general intelligence", a trait which is supposed to be innate.
This means that comparisons of test scores between persons with widely different life experiences and cognitive habits do not reveal their relative innate potentials.
Sternberg, Grigorenko & Kidd (2005) argue that the social construction of race derives not from any valid scientific basis but rather "from people's desire to classify.
[57] Hunt and Carlson disagreed, writing that "Nevertheless, self-identification is a surprisingly reliable guide to genetic composition," citing a study by Tang et al.
Claims that there are innate differences in intelligence between racial and ethnic groups—which go back at least to the 19th century—have been criticized for relying on specious assumptions and research methods and for serving as an ideological framework for discrimination and racism.
[65] In response to the controversial 1994 book The Bell Curve, the American Psychological Association (APA) formed a task-force of eleven experts, which issued a report "Intelligence: Knowns and Unknowns" in 1996.
[69] The 'Flynn effect' — a term coined after researcher James R. Flynn — refers to the substantial rise in raw IQ test scores observed in many parts of the world during the 20th century.
"[71] Flynn himself argued that the dramatic changes having taken place between one just generation and the next pointed strongly at an environmental explanation, and that it is highly unlikely that genetic factors could have accounted for the increasing scores.
They suggest that "much of the beneficial long-term effects typically attributed to breastfeeding, per se, may primarily be due to selection pressures into infant feeding practices along key demographic characteristics such as race and socioeconomic status.
[102][103] A 2003 study found that two variables—stereotype threat and the degree of educational attainment of children's fathers—partially explained the black–white gap in cognitive ability test scores, undermining the hereditarian view that they stemmed from immutable genetic factors.
[60] The view that tests accurately predict future educational attainment is reinforced by Nicholas Mackintosh in his 1998 book IQ and Human Intelligence,[121] and by a 1999 literature review by Brown, Reynolds & Whitaker (1999).
James R. Flynn, surveying studies on the topic, notes that the weight and presence of many test questions depends on what sorts of information and modes of thinking are culturally valued.
[150] Templeton pointed out that racial groups neither represent sub-species nor distinct evolutionary lineages, and that therefore there is no basis for making claims about the general intelligence of races.
A 2012 review by Nisbett et al. (2012a) concluded that the entire IQ gap can be explained by known environmental factors, and Mackintosh found this view to be plausible.
[151] Analysis of polygenic scores sampled from the 1000 Genomes Project has likewise found no evidence that intelligence was under diversifying selection in Africans and Europeans, suggesting that genetic differences make up a negligible component of the observed Black-White gap in IQ.
[162] In a 2014 suite of meta-analyses, along with co-authors Jan te Nijenhuis and Daniel Metzen, he showed that the same negative correlation between IQ gains and g-loading obtains for cognitive deficits of known environmental cause: iodine deficiency, prenatal cocaine exposure, fetal alcohol syndrome, and traumatic brain injury.
[165] Acknowledging the existence of confounding factors, Scarr and Weinberg, the authors of the original study, did not consider that it provided support for either the hereditarian or environmentalist view.
Loehlin (2000) surveys the literature and argues that the blood groups studies may be seen as providing some support to the genetic hypothesis, even though the correlation between ancestry and IQ was quite low.
Mackintosh (2011, p. 338) quotes a statement by Nisbett (2009) to the effect that admixture studies have not provided a shred of evidence in favor of a genetic basis for the IQ gap.
[182] The ethics of research on race and intelligence has long been a subject of debate: in a 1996 report of the American Psychological Association;[60] in guidelines proposed by Gray and Thompson and by Hunt and Carlson;[58][183] and in two editorials in Nature in 2009 by Steven Rose and by Stephen J. Ceci and Wendy M.
Possible preventable causes include malnutrition, infectious diseases such as meningitis, parasites, cerebral malaria, in utero drug and alcohol exposure, newborn asphyxia, low birth weight, head injuries, lead poisoning and endocrine disorders.
