Evidences on the Genetic Influence on Intelligence

Research on heritability of IQ implies, from the similarity of IQ in closely related persons, the proportion of variance of IQ among individuals in a population that is associated with genetic variation within that population. This provides an estimate of genetic versus environmental influence for phenotypic variation in IQ in that population as environmental factors may be correlated with genetic factors. "Heritability", in this sense, "refers to the genetic contribution to variance within a population and in a specific environment".

Intelligence in the normal range is a polygenic trait... [influenced by] over 500 genes.[3,4,5] Twin studies of adult individuals have found a heritability of IQ between 57% and 73%[6] with the most recent studies showing heritability for IQ as high as 80%[7] and 86%.[8]

***-Wikipedia (Heritability of IQ)***

### Expert Opinion

#### Friedrichs (1973)

* This study surveyed 526 members of the American Psychological Association on whether differences in intelligence are based on genetic influence

#### **Survey of Expert Opinion on Intelligence and Aptitude Testing**- Snyderman and Rothman (1987)

* The 1987 “Survey of Expert Opinion on Intelligence and Aptitude Testing” was published in American Psychologist (the official journal of the American Psychological Association). 661 experts completed the questionnaire. The study found that psychologists were in agreement about the heritability of intelligence in that almost all (94%) felt that it substantial role.
	+ -
* There was disagreement regarding accuracy as half of those that felt qualified to reply in this section agreed that there was not enough evidence to estimate heritability accurately. The 214 who thought there was enough evidence gave an average estimate of .596 for the US white population and .57 for the US black population. The study also revealed that the majority (55%) of surveyed experts believed that genetic factors also help to explain socioeconomic differences in IQ.
	+ Expert answers say that the heritability of intelligence is around 60 percent for both blacks and whites, this is replicated by experts in behavioral genetic
* One question was “Which of the following best characterizes your opinion of the heritability of between group differences in IQ?
	+ 14% declined to answer the question.
	+ 24% voted that there was insufficient evidence to give an answer.
	+ 1% voted that the gap was “due entirely to genetic variation”.
	+ 15% voted that it “due entirely to environmental variation”.
	+ 45% voted that it was a “product of genetic and environmental variation”

#### **Mainstream Science on Intelligence**- Gottfredson (1994, 1997 reprinted)

* Mainstream Science on Intelligence gives 25 statements on intelligence- some of these include
	+ "Heritability estimates range from 0.4 to 0.8 ... indicating genetics plays a bigger role than environment in creating IQ differences"
	+ "That IQ may be highly heritable does not mean that it is not affected by the environment ... IQs do gradually stabilize during childhood, however, and generally change little thereafter"
	+ "Although the environment is important in creating IQ differences, we do not know yet how to manipulate it"
	+ "Genetically caused differences are not necessarily irremediable
	+ "The research findings neither dictate nor preclude any particular social policy, because they can never determine our goals. They can, however, help us estimate the likely success and side-effects of pursuing those goals via different means."

* A total of 131 invitations were issued, but only 100 responses were obtained by the deadline. While 52 of these academic researchers agreed with the statements, only 11 out of the 131 asked responded with a disagreement with one or more statements in this article.

* Heritability estimates range from 0.4 to 0.8 (on a scale from 0 to l), most thereby indicating that genetics plays a bigger role than does environment in creating IQ differences among individuals. Questions were sent to 131 researchers, and signed by 52 university professors described as "experts in intelligence and allied fields", including around one third of the editorial board of the journal Intelligence, in which it was subsequently reprinted in 1997.

#### **Intelligence: Knowns and Unknowns**- Neisser (1996)

* Intelligence: Knowns and Unknowns is a report issued by the American Psychological Association. It was subsequently published in an issue of the peer-reviewed journal American Psychologist. This task force consisted of 11 members. (One member was a woman of color if that is relevant to the reader). All members are psychologists with PhDs.
* **"[Heritability] of IQ changes with age:** [heritability] goes up ... from infancy to adulthood... In childhood heritability are of the order of .45 and .35; by late adolescence, [heritability] is around .75... These adult parameter estimates are based on a number of independent studies. The correlation between MZ twins reared apart, which directly estimates [heritability], ranged from .68 to .78 in five studies involving adult samples from Europe and the United States.

#### **Survey of Expert Opinion on Intelligence-** Rindermann et al (2020)

This study surveyed over a hundred intelligence experts on questions that include whether population differences in intelligence are based on genetic influence