[EMAIL PROTECTED] wrote: > As for Chris's posting of the NY Times article on genetic differences > between MZ twins, it seems to me (if I've got the logic right) that it > carries with it an important conclusion for the use of twin studies in > psychology. > > When considering characteristics of MZ twins, under the usual assumption > that they have absolutely identical genetic specification, any > differences between them (in personality, for example) are ascribed to > the effect of the environment. > > But now that we know that they can differ both for epigenetic reasons and > for copy number variation, we can no longer make this claim. Some degree > of the variation beween MZ twins formerly attributed to environmental > effects must instead be due to genetic variation. This means that the > genetic contribution for many psychological factors must be greater than > is estimated by conventional means. > That conclusion fails, I think, to take into account two critical ideas, one old and one new. First the old -- the idea of dividing up "genetic" and "environmental" contributions like additive pieces of so much pie was always mistaken. The modes of combination is much more complicated than that. Second, the new -- epigenetics is utterly rewriting our understanding of how the genotype contributes to the structure and functions of organism. Far LESS than ever before can we say that a particular genetic structure "determines" anything. Epigenetic factors turn on, turn off, and dramatically change the effects of various genes.
It's a whole new game out there and our old claims about the effects of genes will soon look very much like our old claims about the effects of phrenology -- based on a deep misunderstanding of the ways in which things actually work. Regards, Chris -- Christopher D. Green Department of Psychology York University Toronto, ON M3J 1P3 Canada 416-736-2100 ex. 66164 [EMAIL PROTECTED] http://www.yorku.ca/christo/ "Part of respecting another person is taking the time to criticise his or her views." - Melissa Lane, in a /Guardian/ obituary for philosopher Peter Lipton ================================= --- To make changes to your subscription contact: Bill Southerly ([EMAIL PROTECTED])
