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Gary Marcus on Nature–Nurture

To the Editors:

Additional resolution of "the nature–nurture debate" (Gary Marcus, December 2003/January 2004) might be gained by extending the distinction between differences in traits that are due to differences in genes from differences in traits that are due to differential expression of genes. That first kind of difference is the subject of population genetics and the issue addressed is a trait's heritability—i.e., the amount of the variance in a trait that is a consequence of variance in the structure of genes that influence the trait.

For example, most people have five fingers on each hand and most of us think of digit number as a rather biological or genetic trait. But the heritability of digit number is zero. The trait has substantial variance—some people have nine fingers, some have lost a hand and have only five, a boyhood friend of mine from Rocket Club has 8.66 fingers—but as it happens, the frequency of the only gene that contributes to variance in digit number, the gene for polydactyly, does not exceed its mutation rate. Population geneticists dismiss such gene frequencies by convention and so count digit number as having no heritability.

In distinction, polydactyly is relatively common in cats and digit-clipping accidents are so rare that nearly all of the variance in digit number is due to genetic variance. So the heritability of digit number in cats is very high. In this sense, cat digit number is the opposite of human digit number, but we still have a sense that digit number is a trait that has been honed by natural selection in both animals. It is this sense of the evolved nature of traits that sociobiologists commonly address—i.e., traits that have little or no heritability within a species but are very much a product of natural selection.

For example, humans tend to accumulate wealth that they could pass on to strangers or to offspring. As it happens, almost all humans in traditional societies (people that anthropologists study) leave wealth to their children—but people in some cultures leave wealth exclusively to sons while people in other cultures leave wealth to both sons and daughters. Here the variance is across cultures and we do not need to study twins to know that none of this difference is due to differences in genes.

Are cultural differences non-biological, or can cultures be shaped by natural selection to be "IF-THEN providers of opportunity" like the genes in Gary Marcus's African butterflies? Bicyclus anynana are brightly colored when they develop during a warm season and dull brown if they develop in a cooler season—without any change in genetic structure. If cultural inheritance can function like genetic inheritance, what human variable acts like temperature in African Butterflies to determine whether daughters share inherited wealth? Sociobiologists would say marriage pattern—whether a society allows polygynous and monogamous marriage, or only monogamy.

The logic is straightforward. In polygynous societies wives cost wealth and men with multiple wives can increase their reproductive success (more than women could if they had multiple husbands). In such societies variance in male reproductive success is much higher than variance in female reproductive success, with most wealthy men having more than one wife and many children, and a larger number of poor men having no wife and no children. In monogamous societies variance in reproductive success is nearly equal for men and women and the relationship between wealth and reproductive success is not as strong. It follows that parents who leave wealth to sons in polygynous societies will have, on average, more grandchildren than would parents who left wealth equally to daughters and sons. The same dynamic does not apply, or applies to a much lesser degree, in monogamous societies.

In the vast majority of polygynous societies, wealth is left exclusively to sons. In most monogamous societies, a substantial portion of wealth is bequeathed to daughters. The data addressing the polygyny hypothesis have been checked and rechecked. Scientists who set out to challenge the analysis of those data have concluded that they hold up even better under more sophisticated analyses. Still, the correlation could be spurious, and some yet-to-be-tested hypothesis may account for more of the data. My point here is that if the sociobiological explanation is wrong, it is not wrong because the people who find it compelling think that genes trump environment or culture.

Gary Marcus is right. Many people have "misunderstood the nature–nuture debate," and better understanding of how nature fine-tunes behavior can help us fine-tune nurture.

John Hartung, Ph.D.
Associate Editor
Journal of Neurosurgical Anesthesiology
State University of New York
Brooklyn, N.Y.

To the Editors:

I found Gary Marcus's "Making the Mind" essay innovative and stimulating until I reached the last paragraph, in which the author capped his discussion with, "Further studies of gene- environment interactions could eventually lead to a new way of identifying which children who might most profit from special day-care programs or home visits from social workers." (Marcus here is referring to the previous paragraph in which he mentions a study that suggests children with a particular genetic status have a greater tendency to violence . . . if they have experienced earlier mistreatment.)

I think a line has been crossed here and Gary Marcus is "blaming the victim."

What I feel he is claiming, despite his qualification of early trauma, is that there is something wrong or abnormal about the individual child rather than primarily the social environment. This also reminds me of a well-known psychiatrist who, a few years ago, advocated giving psychiatric medication to whole neighborhoods of inner city minority children to prevent them from becoming violent and eventually committing anti-social acts.

Also, I sense that Marcus's coda here has the potential to be extremely reactionary; for, by concentrating focus on the genetic components of individual brain chemistry, he discourages progressive action to change social wrongs and inequalities. Therefore, let us hope, along with John H. Summers in his review in the same issue of this publication—that we don't ever see "The End of Sociology"!

Gloria Calcina del Vecchio
Yardley, Pa.

Gary Marcus replies:

Although I am no expert in the anthropology of wealth in polygamous and non-polygamous societies, I absolutely agree with Dr. Hartung's general points. The contribution of genes to differences between individuals comes not just from their sequences, but from their expression, and that gene expression in turn can be influenced by the environment and hence presumably by culture.

Turning to the second letter, by Ms. del Vecchio, I certainly didn't intend to discourage progressive action to change social wrongs. In fact, I meant to encourage it—but in the context of a nuanced world view in which policymakers recognize that both genetic and social factors contribute to human behavior. The last 25 years of research have made it amply clear that behavior is neither primarily the result of social environment nor primarily the result of genes, but rather comes from a rich and intricate combination of the two. If biologists and sociologists work together, we can make the most of that discovery.

Chomsky on Vietnam

To the Editors:

It pained me ten years ago to take issue with Chomsky on the question of Kennedy's Vietnam withdrawal plans, and it is painful again now. According to James Galbraith (Boston Review, October/November 2003), President Kennedy made a definitive decision in 1963 to withdraw U.S. troops from Vietnam by the end of 1965, regardless of the military situation: a decision to withdraw without victory. Noam Chomsky rejects Galbraith's view and offers two main points in response, both of which he made initially in 1992. As I pointed out in my 1992 rebuttal, he is wrong on both:

1. Chomsky asserts that Kennedy's withdrawal plans were based on false optimism, and thus would have changed if the military balance shifted in a direction unfavorable to the United States. More specifically, Chomsky wrote that Kennedy's withdrawal plans were initiated in response to an "optimistic mid-1962 assessment" (Chomsky, 1992, 10). Leslie Gelb had claimed this in the Pentagon Papers (Beacon, II, 160), but it is not true. The planning was ordered in May 1962, a month after ambassador John Kenneth Galbraith had recommended a political solution based in part on a proposal to the USSR about "phased American withdrawal." One cannot prove that the plans derived from Galbraith's recommendation, but one can and should confidently delink them from what Gelb called "the euphoria and optimism of July 1962."

2. Chomsky holds that claims that Kennedy intended to withdraw without victory were only introduced into the record "after the war became unpopular" in 1968. In 1992, Chomsky argued (p. 11) that the claim that Kennedy had advocated "withdrawal without victory received scant support until well after the Tet offensive of January 1968." I responded then that Daniel Ellsberg had heard in 1964 from his Pentagon boss John McNaughton that McNamara and Kennedy had an understanding to "close out Vietnam by 1965, whether it was in good shape or bad." I noted also that John Newman had reported this in his book that Chomsky was attacking, yet Chomsky wrote then (pp. 21-22), and implies still, that "Newman relies almost exclusively on the virtually meaningless O'Donnell-Mansfield post-Tet reconstructions."

The fact that Chomsky is mistaken on both of these essential points does not prove Galbraith right: but it does leave Galbraith's case standing. I stand by what I wrote in 1992, and reject the charge that I was careless and "seriously misunderstood" Chomsky's argument.

In these circumstances I am sorry Chomsky has chosen to write that it is I who am careless. This will not change my feelings of respect for a man who deserves the world's highest honors, for his devotion to causes ranging from the liberation of East Timor to human rights in Turkey.

Peter Dale Scott
Phayao, Thailand

Noam Chomsky replies:

It pains me too to have to respond. When Scott wrote the "epilogue" to his book to which he refers, 10 years ago, I did not do so, because I was reluctant to bring up such evident flaws in the work of a close personal friend, then and now, whose work in general is of very high standard and significance. But now there seems to be little choice.

Scott's point (1) is based on misreading and faulty logic. First, Scott continues to assume, falsely, that the article to which he refers was based on the Pentagon Papers and Gelb's account. Both the article and the much more detailed book Rethinking Camelot (RC, 1993) make it explicit that they are based primarily on the thousands of pages of documents released after the Pentagon Papers. That error is a large part of the basis of Scott's misreading, repeated by Galbraith. Second, in the article and RC my reference was not to "Kennedy's withdrawal plans" but to McNamara's. May 1962 was of no particular significance in this regard, though it was in others. To quote RC, "In one week of May 1962, Vietnamese Air Force and US helicopter units flew about 350 sorties," part of the general increase in JFK's aggression which was destroying South Vietnam and providing the basis for the optimistic assessments I reviewed. Continuing to quote, the mid-1962 "optimistic assessment of the prospects for successful aggression led Robert McNamara to initiate planning for the withdrawal of US forces from Vietnam, leaving to the client regime the dirty work of cleaning up the remnants." Scott's interpretation of Gelb has no relevance, plainly. For details of how plans developed, reflecting assessments of the prospects, see RC and even the briefer article that Scott continues to misread. We can therefore ignore point (1).

Turning to Scott's point (2), there is no reason to question the post-Tet recollection, but it is of little interest. Doubtless such conversations took place, for the reasons I mentioned: it was understood all along that the war was unpopular, and that some way should be found to get out. But such conversations were regarded as so insignificant that there is no trace of them in the very rich documentary record, or in the memoirs, some of them virtual day-by-day accounts. And McNamara and McNaughton continued to pursue the same basic policies they had proposed and implemented with JFK's approval. Note also that the recognition that the war was unpopular at home, and that the Vietnamese themselves were seeking to negotiate a settlement, was not regarded by JFK as a welcome opportunity to withdraw, but as a problem to be overcome in his unwavering commitment to military victory. We can therefore put point (2) aside as well.

The basic facts remain as reviewed in RC, and the earlier article, and again in the interchange with Galbraith. With reservations, JFK did allow the release of the McNamara-Taylor withdrawal proposals in NSAM 263—Galbraith's and Scott's centerpiece—if it could be carried out "without impairment of the war effort" and with assurance that "the insurgency has been suppressed" or at least sufficiently weakened so that the U.S. client regime (GVN) is "capable of suppressing it" (my italics). Throughout 1962–1963, plans were modified in accord with assessments of what was required for victory. After NSAM 263, reports from the field became more pessimistic and plans accordingly more aggressive, and Kennedy's private and public stand also became more hawkish, as again reviewed in RC. So matters continued after the assassination, while JFK's most dovish advisers praised Johnson for carrying forward JFK's policies with "wise caution" and opposed withdrawal and diplomatic options (Ball, Mansfield), as did Robert Kennedy, who condemned withdrawal without victory as "a repudiation of commitments undertaken and confirmed by three administrations" (May 1965). Not surprisingly, there is nothing in the high-level memoirs written at the time even hinting at a thought of withdrawal without victory, though after opposition to the war became overwhelming, the version changed considerable, as reviewed in RC.

Evidence about historical events is always, of course, subject to interpretation. But it is rare to find a case where it is so consistent and compelling, and so free of significant counterargument.

Originally published in the February/March 2004 issue of Boston Review.

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