

Most Reported Genetic Associations With Intelligence Are Likely False Positives - tokenadult
http://coglab.wjh.harvard.edu/~cfc/Chabris2012a-FalsePositivesGenesIQ.pdf

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tokenadult
Another current article,

Epigenesis for epidemiologists: does evo-devo have implications for population
health research and practice? George Davey Smith Int. J. Epidemiol. (2012) 41
(1): 236-247.

doi: 10.1093/ije/dys016

sums up the most up-to-date research similarly. The author mentions an earlier
author who predicted this outcome in 1927.

"Pearl's prediction (based on biological reasoning) has proved spectacularly
prescient: molecular genetics suggests that of Mendelian influences of
individually tiny effect contribute to the heritability of intelligence. . . .
Indeed, the shuffling of such tiny Mendelian effects could, Pearl said, 'be
relied on, I think, to produce in the future, as it has in the past,
Shakespeares, Lincolns, and Pasteurs, from socially and economically humble
origins.'" (citing Pearl, R. Differential Fertility. Q. Rev. Biol.
1927;2:102-18).

I've had the privilege of meeting Wendy Johnson, a human intelligence
researcher who has an undergraduate degree in mathematics and who has worked
with both the twin studies researchers at Minnesota and with Ian Deary at
Edinborough. Her review articles are very informative on the latest directions
in studies of genetic influences on human intelligence.

The review article "The neuroscience of human intelligence differences" by
Deary and Johnson and Penke (2010) relates specifically to human intelligence:

[http://www.larspenke.eu/pdfs/Deary_Penke_Johnson_2010_-_Neur...](http://www.larspenke.eu/pdfs/Deary_Penke_Johnson_2010_-_Neuroscience_of_intelligence_review.pdf)

"At this point, it seems unlikely that single genetic loci have major effects
on normal-range intelligence. For example, a modestly sized genome-wide study
of the general intelligence factor derived from ten separate test scores in
the cAnTAB cognitive test battery did not find any important genome-wide
single nucleotide polymorphisms or copy number variants, and did not replicate
genetic variants that had previously been associated with cognitive
ability[note 48]."

The review article Johnson, W. (2010). Understanding the Genetics of
Intelligence: Can Height Help? Can Corn Oil?. Current Directions in
Psychological Science, 19(3), 177-182

[http://apsychoserver.psych.arizona.edu/JJBAReprints/PSYC621/...](http://apsychoserver.psych.arizona.edu/JJBAReprints/PSYC621/Johnson%20Current%20Directions%20Psych%20Science%202010%20\(G%20and%20E%20in%20IQ\).pdf)

looks at some famous genetic experiments to show how little is explained by
gene frequencies even in thoroughly studied populations defined by artificial
selection.

"Together, however, the developmental natures of GCA and height, the likely
influences of gene–environment correlations and interactions on their
developmental processes, and the potential for genetic background and
environmental circumstances to release previously unexpressed genetic
variation suggest that very different combinations of genes may produce
identical IQs or heights or levels of any other psychological trait. And the
same genes may produce very different IQs and heights against different
genetic backgrounds and in different environmental circumstances."

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carbocation
> "All of our analyses controlled for graduate/sibling status, age, gender,
> and the interactions of these variables, as well as the first three
> principal components of the genetic data from the full set of 90 genotyped
> SNPs (to account for possible population stratification)."

It is customary to do genomic control using likely-uncorrelated SNPs (i.e.,
excluding the 13 SNPs nominally reported to be in LD with the trait of
interest). That they included these 13 when estimating pop strat from a small
overall number of alleles makes me concerned that they may have
unintentionally "controlled for" the actual effect, if any did exist.

Even then, since they controlled for the first 3 PCs of that data, and I would
assume the 13 candidate SNPs to be in linkage equilibrium, they shouldn't be
getting rid of more than a couple actual associations, yet they find none
replicate. So my observation is probably just a curio.

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aik
Very interesting. Though I'm not finding it overly surprising based on
everything I've read on effects of environment and nurture on growth and
potential.

Few snippets I found interesting:

"These and our other results, together with the failure to date of whole-
genome association studies to find genes associated with g, are consistent
with the view that g is a highly polygenic trait on which common genetic
variants individually have only small effects."

"By far the most plausible explanation for failures to replicate reported
SNP-g (single-nucleotide polymorphisms) associations in our three studies,
however, is that the original studies whose findings we sought to replicate
did not have sufficient sample sizes—and not because of any error in design or
execution."

"Our results add IQ to the list of phenotypes that must be approached with
great caution when considering published molecular genetic associations...
Failing to exercise such caution may hamper scientific progress by allowing
for the proliferation of potentially false results, which may then influence
the research agendas of scientists who do not realize that the associations
they take as a starting point for their efforts may not be real... And the
dissemination of false results to the public may lead to incorrect perceptions
about the state of knowledge in the field, especially knowledge concerning
genetic variants that have been described as “genes for” traits on the basis
of unintentionally inflated estimates of effect size and statistical
significance."

~~~
bromang
why? how is your previous reading about the "effects of environment and
nurture on growth and potential" related to the quoted passages?

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bermanoid
...bracing for the inevitable headlines that claim exactly the opposite of the
first sentence of the abstract: "General intelligence (g) and virtually all
other behavioral traits are heritable."

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jacques_chester
Just to be clear, this doesn't disprove that intelligence is an inheritable
trait; merely that there is so far no clear candidates "an intelligence gene"
and there may never be such.

~~~
mattmcknight
It seems unlikely that something as complex as the behaviors associated with a
test of intelligence would be determined by one specific gene. That we have
found that multiple genes that have a negative effect on intelligence should
be proof enough of that.

