I agree with most of what John says below but I wonder about one of his reasons for why H estimates can be useful. If Heritability estimates are dependent on the amount of environmental variability in the population, does it make sense to say that they will be useful for public policy by telling us how much to expect from environmental manipulations? Might the environmental manipulations have an impact on the heritability estimate that couldn't be predicted from H before the intervention?
Rick Dr. Rick Froman, Chair Division of Humanities and Social Sciences Professor of Psychology Box 3519 John Brown University 2000 W. University Siloam Springs, AR 72761 rfro...@jbu.edu (479) 524-7295 http://bit.ly/DrFroman ------------------------------------------------------------------ From: John Kulig [mailto:ku...@mail.plymouth.edu] Sent: Wednesday, December 18, 2013 10:01 AM To: Teaching in the Psychological Sciences (TIPS) Subject: Re: [tips] Sources of happiness It's a well worn story, but Donald Hebb attacked the heritability (H) concept with the story of raising children in a barrel until 12 (per Mark Twain's suggestion) after which their average IQ would be very low but heritability would = 1 because there is no environmental variation, despite the obvious fact that the environment lowered _average_ IQ. Apparently, though, Hebb makes the misstep to apply the resultant H to a population _other_ than "boys in barrels" .. see Jensen, Arthur R. (1971) (abstract at bottom). But Hebb's "insight" with or without the misstep wasn't anything that anyone with even a modest knowledge of H wouldn't realize. Jeff and Chris are correct that the H is applied to the population and range of environments represented in the data collected. But on the other hand, I think H estimates can be useful. Cultures and environments change, but not to the extent suggested by Mark Twain. They are useful for (1) estimating variance when model/theory building. Our views of personality are changing now that we know a good % is genetic. It points us in the direction of causal factors (genetic or epigenetic) (2) public policy; It is good to know how much to expect from environmental manipulations. It is my understanding the initial goal of Head Start was to raise IQ using existing environmental conditions (pre-school). It did not, though it's a terrific program for other reasons. I suspect (Jeff will know the literature better) H estimates for IQ have not changed much since the early days of Cyril Burt (yes, that guy!). American Psychologist, Vol 26(4), Apr 1971, 394-395. Abstract Comments that the example given by D. O. Hebb (1970) to illustrate the concept of heritability is confusing to readers who do not already understand the concept. Hebb misapplies heritability and arrives at a nonsensical conclusion by estimating heritability in one population and then generalizing it to a quite different population. (PsycINFO Database Record (c) 2012 APA, all rights reserved) ========================== John W. Kulig, Ph.D. Professor of Psychology Coordinator, Psychology Honors Plymouth State University Plymouth NH 03264 ========================== ________________________________________ From: "Jeffry Ricker, Ph.D." <jeff.ric...@scottsdalecc.edu> To: "Teaching in the Psychological Sciences (TIPS)" <tips@fsulist.frostburg.edu> Sent: Tuesday, December 17, 2013 3:28:43 PM Subject: Re: [tips] Sources of happiness On Dec 17, 2013, at 1:01 PM, Christopher Green wrote: My understanding is that here, as in the intelligence debate, proportions of variance attributable to "heredity" are only valid for a given level of variance in the environment. Restrict the range of variability in the environment and "heredity" goes up. Increase the variability of the environment and "heredity" goes down. In short, it can be a highly misleading statistic unless the environment is somehow artificially "standardized." Yes, that was the point I was trying to make with my example. I have never really understood the fascination with heritability estimates. They were developed primarily for agricultural purposes (if I remember correctly: it's been a long time since I studied the history of this area) because knowing the proportion of additive genetic variance to total phenotypic variance helps us to estimate responses to artificial selection. However, even when heritability is zero, genes will still be important contributors to the development of a trait. A heritability of zero simply means that genetic variance is not associated with phenotypic variance. This will occur, for example, when directional selection (or genetic drift) has led to the fixation of genes important for the development of a trait. And there are many other complexities that enter into interpreting heritability. For me, it was useful simply for showing that there were genes in a population that we might want to take a look at. Understanding how these genes were important for the development of a phenotype (i.e., describing gene-environment interactions and epigenetics) was always the goal. I never got very far in this line of work, but many others have since then. Best, Jeff -- --------------------------------------------------------------------------------- Jeffry Ricker, Ph.D. Professor of Psychology --------------------------------------------------------------------------------- Scottsdale Community College 9000 E. Chaparral Road Scottsdale, AZ 85256-2626 Office: SB-123 Phone: (480) 423-6213 Fax: (480) 423-6298 --- You are currently subscribed to tips as: ku...@mail.plymouth.edu. To unsubscribe click here: http://fsulist.frostburg.edu/u?id=13338.f659d005276678c0696b7f6beda66454&n=T&l=tips&o=31543 (It may be necessary to cut and paste the above URL if the line is broken) or send a blank email to leave-31543-13338.f659d005276678c0696b7f6beda66...@fsulist.frostburg.edu --- You are currently subscribed to tips as: rfro...@jbu.edu. To unsubscribe click here: http://fsulist.frostburg.edu/u?id=13039.37a56d458b5e856d05bcfb3322db5f8a&n=T&l=tips&o=31562 (It may be necessary to cut and paste the above URL if the line is broken) or send a blank email to leave-31562-13039.37a56d458b5e856d05bcfb3322db5...@fsulist.frostburg.edu --- You are currently subscribed to tips as: arch...@jab.org. To unsubscribe click here: http://fsulist.frostburg.edu/u?id=13090.68da6e6e5325aa33287ff385b70df5d5&n=T&l=tips&o=31563 or send a blank email to leave-31563-13090.68da6e6e5325aa33287ff385b70df...@fsulist.frostburg.edu
