Reviewing some of the threads here from the past few months, it occurs to me that it would be helpful to the discussion to link to some of the better current review articles about human behavior genetics, and especially research on the genetics of IQ. It is well known, on the one hand, that ALL human behavioral characteristics are heritable. (It is an abuse of language to say "heritable" in this context, but the abuse is conventional and standard in the field.) So we can agree with the professional literature that your tendency to vote for one political party rather than another is heritable. Your number of hours spent each week watching TV is heritable. Your attribution of causes for human differences (e.g., human differences in IQ) is also heritable. Your opinion about regulation of the Internet is heritable. Everything about human behavior is heritable.
Eric Turkheimer has recently been president of the Behavior Genetics Association, and he has the very kind habit of posting most of his peer-reviewed journal articles on his faculty website.
http://people.virginia.edu/~ent3c/vita1_turkheimer.htm
I have the pleasure of meeting many other researchers in human genetics just about weekly during the school year at the University of Minnesota "journal club" Psychology 8935: Readings in Behavioral Genetics and Individual Differences Psychology. From those sources and other sources, I have learned about current review articles on human behavior genetics that help dispel misconceptions that are even commonplace among medically or scientifically trained persons who aren't keeping up with current research.
Johnson, Wendy; Turkheimer, Eric; Gottesman, Irving I.; Bouchard Jr., Thomas (2009). Beyond Heritability: Twin Studies in Behavioral Research. Current Directions in Psychological Science, 18, 4, 217-220
http://people.virginia.edu/~ent3c/papers2/Articles%20for%20Online%20CV/Johnson%20(2009).pdf
is an interesting review article that includes the statement "Moreover, even highly heritable traits can be strongly manipulated by the environment, so heritability has little if anything to do with controllability. For example, height is on the order of 90% heritable, yet North and South Koreans, who come from the same genetic background, presently differ in average height by a full 6 inches (Pak, 2004; Schwekendiek, 2008)."
Another interesting review article,
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%20Online%20CV/Turkheimer%20(2008).pdf
admits the disappointment of behavior genetics researchers.
"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. And over multiple studies and traits the heritabilities go up and down, providing the basis for nearly infinite Talmudic revisions of the grand theories of the heritability of things, perfect grist for the wheels of social science.
"Unfortunately, that fundamental intuition is wrong. Heritability isnӴ 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. In this case it is an estimate of how much the variance of a trait would be reduced if everyone were genetically identical. With a momentӳ thought you can see that the answer to the question of how much variance would be reduced if everyone was genetically identical depends crucially on how genetically different everyone was in the first place."
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_-_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/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 [general cognitive ability] 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. This would be especially the case if height and GCA and other psychological traits are only single facets of multifaceted traits actually under more systematic genetic regulation, such as overall body size and balance between processing capacity and stimulus reactivity. Genetic influences on individual differences in psychological characteristics are real and important but are unlikely to be straightforward and deterministic. We will understand them best through investigation of their manifestation in biological and social developmental processes."
Johnson, W., Penke, L., & Spinath, F. M. (2011). Heritability in the era of molecular genetics: Some thoughts for understanding genetic influences on behavioural traits. European Journal of Personality, 25(4), 254-266.
http://www.larspenke.eu/pdfs/Johnson_Penke_Spinath_2011_-_Heritability.pdf "Despite a few infamous exceptions, the vast majority of scientists who have estimated heritabilities of human behaviour have never been remotely interested in using them for their original purpose of breeding values. In fact, the now well‐established result that all behavioural traits are heritable has been as surprising to these behaviour geneticists as to the behaviourists who believed that people were completely products of their environmental circumstances. Decades ago, when the Zeitgeist locked the door marked ‘Genetic Influences on Behaviour,’ heritability estimates provided the key that opened that door. Having unlocked this door through ambitious and important behaviour genetic studies, we are moving into a room affording a much better (more accurate) view of the developmental processes contributing to behavioural-related outcomes. Now that we are in that room, however, neither the magnitude nor new reports of the existence of heritability in previously unmeasured psychological or behavioural measures alone tells us much of anything. Most importantly, it is not useful as a criterion to judge the biological importance or even construct validity of a psychological measure."
Turkheimer, E. (2011). Genetics and human agency (Commentary on Dar-Nimrod & Heine, 2011). Psychological Bulletin, 137, 825-828. DOI: 10.1037/a0024306
http://people.virginia.edu/~ent3c/papers2/Articles%20for%20Online%20CV/Turkheimer_darnimrod%20comm%20(2011).pdf
reemphasizes the point that a heritability calculation tells us nothing about subject to environmental influences a human trait is. "That heritability depends on the population in which it is measured is one of the most frequently repeated caveats in the social sciences, but it is nevertheless often forgotten in the breach. (For example, it is nearly meaningless for Dar-Nimrod and Heine to note that 'heritability [of intelligence is] typically estimated to range from .50 to .85' [p. 805]. The heritability of intelligence isn’t anything, and even placing it in a range is misleading. Making a numerical point estimate of the heritability of intelligence is akin to saying, 'Social psychologists usually estimate the F ratio for the fundamental attribution error to be between 2.0 and 4.0.') The observation that genotypic variation accounts for 90% of the variation in height in the modern world depends on the variability of genotype and environment relevant to height. Among cloned animals with widely varying diets, body size is perfectly environmental with heritability of 0; in genetically variable animals raised in identical environments heritability is 1.0. This is no mere statistical fine point: it means that the entire project of assessing how essentially genetic traits are in terms of measured heritability coefficients is a fool’s errand."
Chabris, C. F., Hebert, B. M., Benjamin, D. J., Beauchamp, J., Cesarini, D., van der Loos, M., ... & Laibson, D. (2012). Most reported genetic associations with general intelligence are probably false positives. Psychological Science.
http://coglab.wjh.harvard.edu/~cfc/Chabris2012a-FalsePositivesGenesIQ.pdf
"At the time most of the results we attempted to replicate were obtained, candidate-gene studies of complex traits were commonplace in medical genetics research. Such studies are now rarely published in leading journals. Our results add IQ to the list of phenotypes that must be approached with great caution when considering published molecular genetic associations. In our view, excitement over the value of behavioral and molecular genetic studies in the social sciences should be temperedءs it has been in the medical sciencesآy a recognition that, for complex phenotypes, individual common genetic variants of the sort assayed by SNP microarrays are likely to have very small effects.
"Associations of candidate genes with psychological traits and other traits studied in the social sciences should be viewed as tentative until they have been replicated in multiple large samples. 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."
