I’ve just tuned into this ongoing dialogue and, accepting the invitation of John Fentress, I’m putting in my two-cents’ worth.
As for the issue of whether or not "…identical twins reared apart are more similar than identical twins reared together…" is accurate, I have read several of these studies and (a) the results appear sound, and (b) the implications are important. It has been suggested that twins reared together sometimes strive to be different from each other, possibly in an attempt to create a more unique sense of self. Such a dynamic would not be present when twins are reared apart, wherein they could be themselves. I’m sure my own childhood behavior would have been quite different had I had a "doppelganger" at my side.
Likewise, I think that virtually everyone who follows this column (Evolutionary Psychology, after all) would readily agree that the human phenotype is a result of the interactions of both genes and environment. The reason it seems that the role of genes is emphasized over that of environment is because so little is known about exactly HOW genes and environment interact. Consequently, people interested in genes tend to emphasize the known contributions of genes while people more interested in culture, etc., probably are underrepresented in this web forum. This may explain the tendency that you see and also highlights the important function of postings such as yours, reminding us all NOT to oversimplify this discussion. We must never forget the enormous complexity of it all, and of how little we know about how these interactions occur.
As to Richard Lewontin, his claim (which is NOT a fact, as he says) is that "…not a single study of personality traits in human populations successfully disentangles similarity because of shared family experience and similarity because of genes." This is the sort of extremely one-sided position that we all should try to avoid. While it is true in the absolute sense, in practice the use of cross fostering studies (identical twins separated at birth and reared by adoptive families) separates genetic and environmental factors at least as well as most scientists can separate any two highly interactive causative agents. For example, Heston (Science, 167:249-256, 1970) used this technique to successfully demonstrate that the incidence of schizophrenia was concordant with the biological parents (by 40 to 70%), whereas the adoptive parents had no influence on the likelihood of the adoptee developing schizophrenia (1-3%).
Lewontin’s view that "…we know nothing about the heritability of human temperamental and intellectual traits…" is simply his very biased opinion. It is generally accepted that we in fact DO know some things about the heritability of human traits, although the picture is still so murky that Lewontin can get away with such outlandish statements.
Likewise, Lewontin’s argument re: if it is genetically "determined" that we are aggressive and enjoy war, then pacifists either (a) lack that gene, or (b) possess that gene but said gene is not "all powerful" in determining human behavior. This is a classic "straw man" argument, in that Lewontin takes the most extreme position that either (a) one gene totally controls a behavior, or (b) that genes are not the sole determinants of behavior. Do you see that, in posing his argument thus, Lewontin eliminates ALL the middle ground positions, i. e., that genes and environment interact to produce human behavior - the exact position that most all of us would accept as valid? He is trying to force you to accept his absolutist position (genes determine nothing about human behavior) by eliminating the alternative but the equally absolutist (and false) position that "genes determine all," a position Lewontin regards as most odious. If Lewontin had a better argument to support his view, I doubt that he would resort to such deceptive rhetoric.
As to what any humble seeker after truth is to do when reading these contradictory claims is to examine the claims for "trick" arguments, such as above, keep an open mind and keep learning and thinking. And while I agree that we must all be tolerant of dissent, I would like to point out that not all of these experts "disagree with honesty and in good faith…" Lewontin, like Gould and some others in the "genes don’t influence human behavior" camp, are Marxists. That has implications. If you are a committed Marxist (or Behaviorist), you MUST refute any argument espousing any genetic influence on human behavior. Marxism and Behaviorism can only be true if humans are "blank slates" upon which class conflict or contingencies of reinforcement are the only determinants of human behavior. Lewontin’s attitude is similar to that of the Creationists, in that they know, a priori, that evolution is wrong (that’s their fervent belief) and then consider only evidence that favors their view. A Creationist who accepts the facts of evolution can’t still be a Creationist. Everyone enters this debate with a personal agenda - a bag of biases, religious beliefs, and political persuasions. Since the issues we discuss herein touch on almost every aspect of the meaning of being human, I would be amazed if these issues did NOT touch peoples’ hot buttons, eliciting both dogmatically wrong arguments and plenty of heated emotions.
I think that there is a "correct" approach to take, Brian, and you are pretty much there. Combine the clearly defensible position that human behavior is a consequence of the complex interactions of genes and environment (with the balance of power yet to be determined by further research) with your "well-disposed skepticism" towards any extreme claims, and progress can be made. And although our respective views regarding the magnitude of the genetic contribution to human behavior clearly differ, I enjoy your comments and would hate to see you leave. I hope that I’m not the only one.