Most Reported Genetic Associations with Intelligence are Probably False
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Re: Most Reported Genetic Associations with Intelligence are Probably False
#2Nature vs nurture is hard to separate, especially when genes and culture tend to be 'handed down' to the same individuals.
However I'm curious that they chose to use the very-powerfully-determined-by-genes features of Alzheimers and BodyMassIndex as their control. Surely there are other genetic traits that are not 'disorders' which could have been referenced? Breakdowns in physical function would naturally have larger measurable effects than, say, alcohol metabolism rates or whatever.
Re: Most Reported Genetic Associations with Intelligence are Probably False
#3Nature vs nurture is hard to separate, especially when genes and culture tend to be 'handed down' to the same individuals. However I'm curious that they chose to use the very-powerfully-determined-by-genes features of Alzheimers and BodyMassIndex as their control. Surely there are other genetic traits that are not 'disorders' which could have been referenced? Breakdowns in physical function would naturally have large…
Surely there are other genetic traits that are not 'disorders' which could have been referenced?
Studies of the issue of "missing heritability" have often investigated height (bodily stature), which has a very high calculated heritability (resemblance among close relatives) but which must be influenced by hundreds of genes, many of very small effect. Even very extensive genome-wide association studies (GWAS) in large samples find NO gene with large effect on height, and fail to detect most of the presumed associations with height in gene associations investigated in such studies.
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/...
looks at some famous genetic experiments to show how little is explained by gene frequencies even in thoroughly studied populations defined by artificial selection.
Re: Most Reported Genetic Associations with Intelligence are Probably False
#4"These and our other results, together with
the failure of whole-genome association studies of g to date, are consistent with general
intelligence being a highly polygenic trait on which common genetic variants individually have
only small effects."
This doesn't seem like a surprising result to me. What is being claimed is not "intelligence is not genetic" but it is that "heritability of intelligence is complex". For something that appears as complicated as human intelligence, wouldn't this be expected?
Re: Most Reported Genetic Associations with Intelligence are Probably False
#5Note that the article is not saying that intelligence is not heritable. In fact it makes it quite clear that despite the controversy, the opposite is true:
> Although the exact figures have been the topic of much debate, the claim that IQ is at least moderately heritable is widely accepted. IQ may in fact be similar in heritability to the physical trait of height
What the article is saying is that intelligence cannot be tied to particular genes:
> We sought [and failed] to replicate published associations between 12 specific genetic variants and g using three independent, longitudinal datasets
It just goes to show that there isn't necessarily one particular factor you can pick out to predict intelligence; it is a combination of many things.
(I shall attempt to avert the impending discussion about the word "intelligence" by clarifying that the sense I am using that word is in the same specific manner that the article is: as an objective measure that is statistically correlated with other measures).
Re: Most Reported Genetic Associations with Intelligence are Probably False
#6Note that the article is not saying that intelligence is not heritable. In fact it makes it quite clear that despite the controversy, the opposite is true: > Although the exact figures have been the topic of much debate, the claim that IQ is at least moderately heritable is widely accepted. IQ may in fact be similar in heritability to the physical trait of height What the article is saying is that intelligence cannot…
It may be useful for the discussion here to define what "heritable" means. I like what Eric Turkheimer, a psychologist who investigates the heritability of human intelligence, says about that.
"But back to the question: What does heritability mean? Almost everyone who has ever thought about heritability has reached a commonsense intuition about it: One way or another, heritability has to be some kind of index of how genetic a trait is. That intuition explains why so many thousands of heritability coefficients have been calculated over the years. Once the twin registries have been assembled, it's easy and fun, like having a genoscope you can point at one trait after another to take a reading of how genetic things are. Height? Very genetic. Intelligence? Pretty genetic. Schizophrenia? That looks pretty genetic too. Personality? Yep, that too. . . .
"Unfortunately, that fundamental intuition is wrong. Heritability isn't an index of how genetic a trait is. A great deal of time has been wasted in the effort of measuring the heritability of traits in the false expectation that somehow the genetic nature of psychological phenomena would be revealed. There are many reasons for making this strong statement, but the most important of them harkens back to the description of heritability as an effect size. An effect size of the R2 family is a standardized estimate of the proportion of the variance in one variable that is reduced when another variable is held constant statistically."[1]
[1] Turkheimer, E. (2008, Spring). A better way to use twins for developmental research. LIFE Newsletter, 2, 1-5
http://people.virginia.edu/~ent3c/papers2/Articles%20for%20O...
Re: Most Reported Genetic Associations with Intelligence are Probably False
#7This whole field seems likely to be a case study supporting http://xkcd.com/882/.
But the research does have a questionable assumption. On p 5 it says, "Such a result would not likely be due to differences in the methods used to generate g in the various datasets under comparison, since g is consistently measured by a wide variety of tests."
This is true. However it is also true that, as http://vserver1.cscs.lsa.umich.edu/~crshalizi/weblog/523.htm... points out, that all evidence we have is consistent with g being a correlation between different ways of weighting a large number of independent factors. If so, then it is easy to have two test measuring g that are fairly well correlated with each other, one of which picks up a particular factor and the other does not. If a gene affects that factor, then the test you use to measure to find these correlations will matter.
Re: Most Reported Genetic Associations with Intelligence are Probably False
#8The now famous paper Why Most Published Research Findings Are False (http://www.plosmedicine.org/article/info:doi/10.1371/journal...) singles out genetics as a field particularly prone to false positive findings.
Re: Most Reported Genetic Associations with Intelligence are Probably False
#9I would assume that many behaviours (including language itself) are inherited - and yet have nothing whatever to do with genetics. How would you control for this?
Only last week, we had an article on here about how vocabulary in very young children was a function of how much parents talked to their children - with marked differences between economic groups[1]. There are many many systematic errors in this kind of data, and I have no good (ethical) suggestions in how to eliminate them.
Re: Most Reported Genetic Associations with Intelligence are Probably False
#10" These and our other results, together with the failure of whole-genome association studies of g to date, are consistent with general intelligence being a highly polygenic trait on which common genetic variants individually have only small effects. " This doesn't seem like a surprising result to me. What is being claimed is not "intelligence is not genetic" but it is that "heritability of intelligence is complex". F…
Things that are "expected" still need to be tested. Also, http://lesswrong.com/lw/im/hindsight_devalues_science/.