Genes, Heritability, ‘Race’, and Intelligence: Misapprehensions and Implications

A large body of experimental literature demonstrates causal connections between a variety of genetic variants of multiple types and intellectual disability.

“A large body of experimental literature demonstrates causal connections between a variety of genetic variants of multiple types and intellectual disability.”

• cites [19] Neri, 2018, X-linked intellectual disability update 2017, Am. J. Med. Genet. A sourceSupported

Mutations affecting the functioning of products produced by more than 100 genes on the X-chromosome alone have been associated with intellectual disability.

“Mutations affecting the functioning of products produced by more than 100 genes on the X-chromosome alone have been associated with intellectual disability [19].”

• cites [19] Neri, 2018, X-linked intellectual disability update 2017, Am. J. Med. Genet. A sourceSupported

Variation in the lengths and number of fingers on human hands results from genetic variation.

“The variation in the lengths and number of fingers on human hands that results from genetic variation, and there is such variation [14,15], has helped to identify the genes that are involved in constructing human hands in development through the stages from embryo to fetus to neonate.”

• cites [14] Umair, 2018, Clinical Genetics of Polydactyly: An Updated Review, Front. Genet. sourcePartly supported

  The Abstract (page unavailable) identifies extra fingers or toes as a hereditary anomaly and names genes associated with polydactyly, supporting genetic variation in finger number. The paper does not establish that variation in the lengths of human fingers results from genetic variation; a search for finger and digit length did not find that point. (LLM, conf=0.88)

  Experimental — accuracy not yet measured
• cites [15] Temtamy, S.A., and Aglan, M.S. (2008). Brachydactyly. Orphanet J. Rare Dis., Available online: http://www.ojrd.com/content/3/1/15. sourceSupported

Genetic variation at many genomic loci substantially influences variation in intelligence and other cognitive capacities or behaviors.

“The evidence is overwhelming that genetic variation at many genomic loci substantially influences variation in intelligence and other cognitive capacities or behaviors.”

• cites [19] Neri, 2018, X-linked intellectual disability update 2017, Am. J. Med. Genet. A sourcePartly supported

  The Abstract identifies 141 X-linked genes associated with intellectual disability, supporting the point that variation at many loci can affect intellectual functioning. The paper does not establish the broader claim about variation in intelligence across the population or in other cognitive capacities and behaviors; its focus is X-linked intellectual disability. (LLM, conf=0.86)

  Experimental — accuracy not yet measured

Genetic variation affects variation in brain development and neural and cognitive functioning.

“Another basic reality beyond dispute is that genetic variation affects variation in brain development and neural and cognitive functioning.”

• cites [19] Neri, 2018, X-linked intellectual disability update 2017, Am. J. Med. Genet. A sourceSupported

There is more genetic variation among the people of Africa than among the people living on all other continents.

“there is more genetic variation among the people of Africa than among the people living on all other continents [25].”

• cites [25] McGuire, 2020, The road ahead in genetics and genomics, Nat. Rev. Genet. sourceSupported

Violence in a neighborhood can depress measures of cognitive ability for school-aged (5-17 years old) children in that community.

“Patrick Sharkey has published several studies demonstrating that violence in a neighborhood can depress measures of cognitive ability for school-aged (5–17 years old) children in that community [22,23].”

• cites [22] Sharkey, 2010, The acute effect of local homicides on children’s cognitive performance, Proc. Natl. Acad. Sci. USA sourcePartly supported

  Materials and Methods identifies a sample aged 5–17, and the Discussion reports that recent local homicides reduced children’s cognitive-test performance. But the reported effect was acute and found among African-American children, not Hispanic children; the claim’s broader wording about neighborhood violence and children generally omits those limits. (LLM, conf=0.86)

  Experimental — accuracy not yet measured
• cites [23] Laurito, 2019, School climate and the impact of neighborhood crime on test scores, RSF sourcePartly supported

  The Discussion reports lower English language arts test scores after neighborhood-violence exposure for sixth- to eighth-grade students attending the least safe schools. It finds no overall significant effect or effect on math scores. The claim extends this conditional test-score finding to children aged 5–17 and describes the outcome more broadly as cognitive ability; the paper does not establish those broader points. (LLM, conf=0.85)

  Experimental — accuracy not yet measured

Stressful experiences early in life can affect future behavior by influencing the rates of gene transcription and translation in brain cells.

“Another recent publication offers evidence of the potential for stressful experiences early in life to affect future behavior by influencing the rates of gene transcription and translation in brain cells [24].”

• cites [24] Kronman, 2021, Long-term behavioral and cell-type-specific molecular effects of early life stress are mediated by H3K79me2 dynamics in medium spiny neurons, Nat. Neurosci. sourcePartly supported

  The Introduction and Discussion (pages not provided) link early-life stress to altered gene transcription in nucleus accumbens neurons and greater susceptibility to stress-related behavior in adult mice. The paper does not establish that altered rates of translation mediate those behavioral effects, so that part of the claim is unsupported. (LLM, conf=0.86)

  Experimental — accuracy not yet measured

Such genetic influence cannot be reasonably interpreted as proof that one group of people is cognitively superior to another.

“Such genetic influence cannot, therefore, be reasonably interpreted as proof that one group of people is cognitively superior to another.”

Some genetic influences on cognitive capacities or behaviors may arise through interactions between genetic and environmental factors and be at least in part culturally mediated.

“Still, some of these influences may arise through interactions between genetic and environmental factors and be, at least in part, culturally mediated.”

The value of heritability is not an intrinsic property of a gene, a trait, or a gene-trait pair for a given population or whole species.

“the value of the heritability is not an intrinsic property of a gene, a trait, or a gene-trait pair for a given population or whole species.”

Due to epistasis and gene-environment interactions and other factors, the phenotypic implications of possession of a particular allele may vary significantly in different individuals (variable penetrance or expressivity).

“due to epistasis and gene-environment interactions and other factors, the phenotypic implications of possession of a particular allele may vary significantly in different individuals, referred to as variable penetrance, the likelihood given possession of a specific allele that an associated trait is observed, or expressivity, the extent to which the trait associated with the gene in question is”

• cites [17] Udayangani, S. (2021, December 22). Difference Between Penetrance and Expressivity. Available online: https://www.differencebetween.com/difference-between-penetrance-and-vs-expressivity/.Not checked yet

  Not checked in the free run.

• cites [18] Miko, 2008, Phenotype variability: Penetrance and expressivity, Nat. Educ.Not checked yet

  Not checked in the free run.

A genotype that generates a more productive phenotype than another in one environment might generate a less productive phenotype in a different environment.

“a genotype, we can call A, that in comparison to genotype B generates a more productive phenotype in environment no. 1 might generate a less productive phenotype than B in environment no. 2.”

The extent of the impact of allelic variation at a particular locus on variation in a trait may either correlate or interact with one or more environmental factors such that disentangling the relative importance of genetic versus environmental factors for individuals becomes highly challenging or practically impossible.

“The extent of the impact of allelic variation at a particular locus on variation in a trait, such as happiness, cognitive function, height, eye color, or skin color may either correlate or interact with (i.e., depend on) one or more environmental factors such that disentangling the relative importance of genetic versus environmental factors for individuals becomes highly challenging or practically”

Even highly heritable traits can, in principle, be modified by manipulations of judiciously selected environmental factors.

“even highly heritable traits can, in principle, be modified by manipulations of judiciously selected environmental factors.”

Even a very high percentage of heritability for a specific phenotype has no implications for how amenable to change that phenotype will be if exposed to altered environmental inputs, such as medical or social interventions that were not previously present in the study population.

“even a very high percentage of heritability for a specific phenotype has no implications for how amenable to change that phenotype will be if exposed to altered environmental inputs, such as medical or social interventions that were not previously present in the study population.”

Changes in the relevant allele frequency distributions or in the presence or distribution of environmental factors can lead to alterations in the degree of heritability.

“changes in the relevant allele frequency distributions (which are not merely possible but over sufficiently long periods of time likely) or in the presence or distribution of environmental factors can lead to alterations in the degree of heritability.”

The correlation between allelic variation at loci that encode proteins relevant to melanin production and other traits is likely mediated primarily by cultural beliefs, not the mechanisms of biochemistry and cell biology.

“the correlation between allelic variation at loci that encode proteins relevant to melanin production and other traits is likely mediated primarily by cultural beliefs, not the mechanisms of biochemistry and cell biology.”

It is extremely unlikely that it is currently possible to accurately determine the extent to which interactions between genetic variation that has no direct impact on the brain and environmental variation affect putative group differences in measures of brain function.

“it is extremely unlikely that it is currently possible to accurately determine the extent to which interactions between genetic variation that has no direct impact on the brain and environmental variation affect putative group differences in measures of brain function.”

Determining a high heritability for a trait does not automatically argue against actions in social policy, medical, or other practical contexts whereby environmental factors would be modulated.

“determining a high heritability for a trait does not automatically argue against actions in social policy, medical, or other practical contexts whereby environmental factors would be modulated.”

The influence of genetic variation on a trait can be indirect and mediated almost completely by factors other than inherent biochemical mechanisms such as culturally grounded practices and/or beliefs, such that what may be taken to be a genetic effect may be as or more appropriately viewed as originating, at least in part, from environmental causes.

“The influence of genetic variation on a trait can be indirect and be mediated almost completely by factors other than inherent biochemical mechanisms such as culturally grounded practices and/or beliefs such that what may be taken to be a genetic effect may be as or more appropriately viewed as originating, at least in part, from environmental causes”

The implicit assumption that genes involved in influencing IQ in some putative racial groups are clearly and unalterably superior to those same genes in other racial groups, creating a static hierarchy, is unjustified.

“The implicit assumption of some participants in the controversy that genes involved in influencing IQ in some putative racial groups are clearly and unalterably superior to those same genes in other racial groups, creating a static hierarchy, is unjustified.”

• Also stated in: § 6. The Distribution of Human Genetic Variation · plain

  “the implicit assumption made by some participants in the arguments about genes, race, and intelligence that there is a clear and absolute hierarchy of genotypes in terms of the cognitive abilities they can produce is not justified in the absence of data that I have never seen.”

The magnitude of heritability for a given trait is influenced by the particular allele frequency distributions at the relevant loci in the population studied and for which other populations may differ substantially.

“The magnitude of heritability for a given trait is influenced by the particular allele frequency distributions at the relevant loci in the population studied and for which other populations may differ substantially.”

Lumping together all Africans as one race is scientifically questionable.

“So, lumping together all Africans as one race is scientifically questionable.”

In the American context, genetic variation affecting skin color might have an impact on outcomes presumed to depend in part on cognitive capability.

“it should be possible to appreciate how genetic variation affecting skin color might have an impact on outcomes presumed to depend in part on cognitive capability.”

What appears to be a genetically determined outcome is, in fact, due to interactions between a gene or genes and aspects of the environment.

“The key takeaway lesson is that what appears to be a genetically determined outcome is, in fact, due to interactions between a gene or genes and aspects of the environment.”

Environmental factors can clearly decrease putatively inherent IQ.

“there are clearly environmental factors that can decrease putatively inherent IQ.”

• cites [11] Galiciolli, 2022, IQ alteration induced by lead in developed and underdeveloped/developing countries: A systematic review and a meta-analysis, Environ. Pollut. sourceNot checked — no full text of the source

Dividing the people of the world into clear, discrete racial groups is misleading because the variation across the globe is most appropriately regarded as roughly continuous.

“dividing the people of the world into clear, discrete racial groups is misleading because the variation across the globe is most appropriately regarded as roughly continuous, as would be anticipated from an evolved and evolving lineage of organisms that can move around.”

The genetic variation that influences variation in measures of cognitive performance within a population is not necessarily identical to the genetic variation that influences variation in mean measures of cognitive performance between populations.

“the genetic variation that influences variation in measures of cognitive performance within a population is not necessarily identical to the genetic variation that influences variation in mean measures of cognitive performance between populations.”

Human genetic variation exhibits patterns that are correlated with variation in the predominant geographic origins of the ancestors of people alive today.

“It is clear that human genetic variation exhibits patterns that are correlated with variation in the predominant geographic origins of the ancestors of people alive today.”

The vast majority of traits in the vast majority of people are the result of both genetic and environmental factors.

“The vast majority of traits in the vast majority of people are the result of both genetic and environmental factors [16].”

• cites [16] Moore, D.S. (2002). The Dependent Gene: The Fallacy of Nature vs. Nurture, W. H. Freeman & Co.Not checked yet

  Not checked in the free run.

Accepting a role for genetic variation in influencing variation in intelligence and other cognitive capacities or behaviors does not necessitate concluding that individuals with what are defined as lesser apparent capabilities cannot be helped by changes in environmental factors.

“accepting a role, even an important role, for genetic variation in influencing variation in intelligence and other cognitive capacities or behaviors in no way necessitates concluding that individuals with what are defined as lesser apparent capabilities cannot be helped by changes in environmental factors.”

The genetic loci involved in intellectual disability cases encode proteins that participate in processes such as synapse formation, synaptic plasticity, neuronal migration, chromatin remodeling, and protein half-life.

“The genetic loci involved in these cases have been demonstrated in other studies to encode proteins that participate in such processes as the formation of synapses (subcellular structures that mediate communication between neurons), synaptic plasticity, neuronal migration during brain development, chromatin remodeling, which influences the amount of gene transcription (mRNA production) and”

It can be extremely difficult to disentangle effects due to genetic variations from effects that depend on mechanisms independent of variations in nucleotide sequence.

“the results already reported suggest that it can be extremely difficult to disentangle effects due to genetic variations (differences in nucleotide sequence) from effects that depend on mechanisms independent of variations in nucleotide sequence.”

The range of environmental factors influencing relevant measures of performance thought to depend on brain function is extremely difficult to fully delineate or assess in terms of quantitative significance.

“the range of environmental factors influencing relevant measures of performance thought to depend on brain function (e.g., educational attainment, employment, and professional achievement) is extremely difficult to fully delineate or assess in terms of quantitative significance.”

Eliminating or reducing the impact of environmental factors that decrease putatively inherent IQ, especially early in life, can potentially increase IQ relative to what it might have been if those negative influences were not eliminated or attenuated.

“Therefore, eliminating or reducing the impact of such factors, especially early in life, can potentially increase IQ relative to what it might have been if those negative influences were not eliminated or attenuated.”

The idea of utterly separate and fixed racial groupings is not sensible.

“the idea of utterly separate and fixed racial groupings is not sensible.”

The heritability of a phenotype within a population does not determine the extent to which genetic variation is responsible for mean differences between populations that can be differentiated with respect to factors that exert significant influence on variation in that phenotype.

“the heritability of a phenotype within a population does not determine the extent to which genetic variation is responsible for mean differences between populations that can be differentiated from one another with respect to factors that exert significant influence on variation in a phenotype of interest.”

The heritability value for a trait might be expected to vary depending on the environmental factors operative within a population and the distributions of the impacts of those environmental factors on the members of a population, as well as the precise manner by which the trait is assessed or measured.

“So, the heritability value for a trait might be expected to vary depending on the environmental factors operative within a population and the distributions of the impacts of those environmental factors on the members of a population, as well as the precise manner by which the trait is assessed or, if quantitative, measured.”

Careful studies of many phenotypes in a variety of organisms in different environments reveal that relationships between phenotype and environment can be variable in comparing one genotype to another.

“Careful studies done of many phenotypes in a variety of organisms in different environments reveal that these relationships can be variable in comparing one genotype to another.”

• cites [6] Lewontin, R. (2000). The Triple Helix: Gene, Organism, Environment, Harvard University Press.Not checked yet

  Not checked in the free run.