In a previous post I discussed the following article, which shows that in the case of extreme poverty (by US standards) the genetic heritability of intelligence is drastically reduced. It is the first study I had heard of which really showed a clear case of nonlinear response to environment (excluding cases of severe malnutrition). See related discussion of heritability and regression here.
Turkheimer, E., Haley, A., D'Onofrio, B., Waldron, M & Gottesman, I. (2003). Socioeconomic status modifies heritability of IQ in young children. Psychological Science, 14, 623-628.
In this paper he discusses interactions between genes and environment, and why they make social science hard:
Turkheimer, E. (2004). Spinach and Ice Cream: Why Social Science Is So Difficult. In. L. DiLalla (Ed). Behavior genetics principles: Perspectives in development, personality, and psychopathology. (pp. 161-189). Washington, DC, US: American Psychological Association.
Recently, he gave the following talk at Stanford, emphasizing how the problems faced by state of the art genomic science (e.g., genome wide association or gwa studies) mirror those of social science. That is, outcomes depend nonlinearly on a large number of (possibly correlated) causes. This is the "Gloomy Prospect" first referred to by psychologist Robert Plomin. I highly recommend the audio version -- Turkheimer is a good speaker and the discussion at the end is interesting.
Gloomy Prospect Wins
slides (ppt) , iTunes audio
The contemporary era has seen a convergence of genomic technology and traditional social scientific concerns with complex human individual differences. Rather than finally turning social science into a replicable hard-scientific enterprise, genomics has gotten bogged down in the long-standing frustrations of social science. A recent report of an extensive genome wide association study of human height demonstrates the profound difficulties of explaining uncontrolled human variation at a genomic level. The statistical technologies that have been brought to bear on the problem of genomic association are simply modifications of similar methods that have been used by social scientists for decades, with little success. The motivation for the statistical methods in genomics is the same as it is in traditional social science: An attempt to discern linear causation in complex systems when experimental control is not possible.
In the talk Turkheimer gives the following definition of social science, which emphasizes why it is hard:
Social science is the attempt to explain the causes of complex human behavior when:
There are a large number of potential causes.
The potential causes are non-independent.
Randomized experimentation is not possible.
He proposes that genomics will also be hard for similar reasons. Final slide:
The question is not whether there are correlations to be found between individual genes and complex behavior— of course there are—but instead whether there are domains of genetic causation in which the gloomy prospect does not prevail, allowing the little bits of correlational evidence to cohere into replicable and cumulative genetic models of development. My own prediction is that such domains will prove rare indeed, and that the likelihood of discovering them will be inversely related to the complexity of the behavior under study.
Also see his wonderful essay The Fundamental Intuition (at Cato Unbound).
ReplyDeleteHi Steve,
ReplyDeleteSo it seems by Turkheimer's work that intervention at the lowest rungs of the economic ladder would have the biggest effect on the future prospects of a child. By this argument, we should pour resources into programs for the very poor.
On the flip side, what does the data say on programs for talented and gifted children? Do children that come out of these programs go on to higher achievement than children that do not? Given that environment may not enhance IQ once you are beyond a threshold, it could influence other things like exposure to like-minded peers, ideas and tools for maximizing their talents. This may not make you smarter but does it make you more productive?
It's good to see social scientists like Plomin finally realizing the inherent limitations and "gloominess" of using genetics in explaining complex social traits. He could have simply walked down to the molecular biology department and asked a working geneticist or walked to the philosophy department and asked to speak with a philosopher of science specializing in the philosophy of biology. He would have been set proper long ago.
ReplyDeleteThough my speciality is not philosophy of biology, I am studying philosophy and know of some work that has been done in the area of philosophy of biology.
For example, this paper by Ned Block is a rewrite of an earlier one he wrote from the early 70s detailing the inherent limitations of heritability.
http://www.nyu.edu/gsas/dept/philo/faculty/block/papers/Heritability.html
This book was written about ten years ago and it touches on the explanatory limitations built into both classical and molecular genetics in its use in the domain of social science.
http://www.amazon.com/Genetics-Reductionism-Cambridge-Studies-Philosophy/dp/0521637139/ref=sr_1_1?ie=UTF8&s=books&qid=1224504222&sr=8-1
I agree with Sarkar that classical genetics will never give any meaningful, nontrivial and scientifically significant explanation of any complex trait. Molecular genetics is similarly handicaped as of now and even in the far future. it almost certainly will not yield major results in explaning the vast majority of complex traits. This is simply built into the nature of the science of genetics and its relation to social science.
"SOCIOECONOMIC STATUS MODIFIES HERITABILITY OF IQ IN YOUNG CHILDREN
ReplyDeleteEric Turkheimer, Andreana Haley, Mary Waldron, Brian D'Onofrio, and Irving I. Gottesman"
A few points:
1 - The study included only young children and does not make any attempt to extrapolate that all other findings of significant increases in h^2 by age 17 are in any way invalid. The effects of the shared environment vanish at around age 12.
2 - Turkheimer began his paper by recognizing that the heritability of cognitive ability in childhood is well established.
3 - Turkheimer made no attempt whatsoever to determine what components of SES he was measuring. There are three obvious items to consider: macro environmental, micro environmental, and genetic. All work to date indicates that the first of these can be found in children, but that it is absent in late adolescents; by late adolescence, all of the environmental component is of the second type; and that genetic intelligence is the largest determinant of SES.
4 - Turkheimer says that the effect he observed was related to the homes in which the children were raised. This is interesting, since it relates to the adoption studies which show that after childhood there is no adult IQ correlation between biologically unrelated children who were reared together in the same home.
5 - Turkheimer discusses in some detail that SES is not strictly an environmental variable, since it is known to be (statistically) caused by the intelligence of the parents. He points out that the models he used "cannot determine which aspect of SES is responsible for the interactions" observed.
Thank you very much for transcribing Turkheimer on the nature of social science...I was dreading having to re-listen to that podcast to get the quote for a paper I'm writing!
ReplyDelete