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EPIDEMIOLOGY AND SOCIETY: A Forum on Epidemiology and Global Health

The Slavery Hypertension Hypothesis: The Authors Respond

Kaufman, Jay S.; Hall, Susan A.

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We appreciate the comments of Blackburn, 1 Grim and Robinson 2 and Weiss 3 on our essay discussing the Slavery Hypertension Hypothesis. 4 The editors have allowed us a brief response to these thoughtful remarks, and we take this opportunity to pursue some areas of apparent disagreement, and to clarify a few points of potential misunderstanding.

Blackburn 1 eloquently summarizes the fundamental scientific issues at hand and then expresses some concern about the “temperature” of the debate. Along with the other commentators, he suggests that opinions about the Slavery Hypothesis might conform to political ideology. This suggestion has also been made previously, as exemplified by Dimsdale's ad hominem reference to critics of the Slavery Hypothesis as “left-thinking people.”5, p.325 Although our essay discussed biological essentialism as an ideologic underpinning for the Slavery Hypothesis, essentialist theories do not appear to reside in a particular location on the political spectrum. Although such notions often receive fawning attention from political conservatives, 6,7 they are embraced broadly as folk wisdom throughout our society and surface frequently in popular and scientific discussions of race and gender. 8 Consequently, we assume no facile connection between criticism of the Hypothesis and any political ideology. We merely argue that scientific consensus should conform to evidence rather than mere assertion. If it is polemic to insist on evidence, then we would contend that science should be more polemic, not less so.

Grim and Robinson 2 interpret our essay as a call to end all genetic research that might stigmatize ethnic populations. We make no such recommendation against genetic research broadly, only against speculation in the guise of research. In their commentary, Grim and Robinson speculate that future research will identify genotypes for salt sensitivity, and that these will be more common in Western-Hemisphere Blacks. Our essay demonstrated that, on the basis of little more than this sort of wishful thinking, the Slavery Hypothesis has become a standard feature of medical textbooks and of both professional and popular credence.

Despite the revolution in molecular techniques that has transformed genetic epidemiology, Grim and Robinson2 cite no recently published hypertension research. Rather, the new data cited in their commentary are historical and are attributed to the study by Eltis and colleagues. 9 The mortality figures listed in the commentary, however, bear no discernible resemblance to those in the citation the authors provide. For example, they report the mortality during the “coasting period” (when ships sailed up and down the African coast until filled) as 12%. What the cited reference describes, however, is that only 12% of ships “coasted” (specifically, that 11.5% of vessels in the dataset traded at two or more places). 10, p. 31 Other estimates reported by Grim and Robinson to be “gleaned from the William and Mary Quarterly Review” are similarly mysterious in origin. Only the “Middle Passage” mortality statistic relates to the cited reference, and here the authors conflate “Angola” with Walsh's “West Central Africa” (a much broader region), perhaps in an effort to make a connection with Joseph Miller's work cited in earlier expositions. This lack of clarity in the use of historical data typifies the evidence mustered to support the Slavery Hypothesis to date. 11

Weiss 3 asserts that we “argue that the Hypothesis must be wrong” and that we do so “like good lawyers” (as opposed to good scientists?). The purpose of our essay was to suggest that no appreciable evidence has been presented in support of the Hypothesis, and that it is therefore alarming to find the idea so widely disseminated and accepted in both scientific and popular arenas. Weiss does not dispute our assertion about the paucity of evidence, but rises to the defense of the plausibility of the idea. In the Swiss courtroom analogy, the Slavery Hypothesis is labeled a “credible allegation.” The argument for this putative credibility, however, draws on the same sources as the Slavery Hypothesis itself. “There is considerable evidence,” Weiss begins, “that African-American populations are more susceptible to hypertension than other groups.” If by “susceptible” he means that they exhibit a higher prevalence than white Americans, the statement is uncontroversial and not particularly pertinent. If, however, he means to suggest that under identical environmental conditions, black Americans would experience a higher risk of hypertension than would white Americans, the statement is scientifically indefensible. We do not know all the relevant environmental factors (as Weiss points out later in the same sentence) and, furthermore, we know a priori that these relevant factors are likely to be distributed differentially between blacks and whites by virtue of the crucial social distinction between these groups. 12

With suitable caveats, Weiss 3 offers his opinion that the racial disparity might (but just might) arise from “tractably simple genetic differences” between the groups, in interaction with contemporary environments. The support presented for this opinion centers on an analogy to Neel's “thrifty genotype,” a trait that appears to characterize every human population subjected to the relevant environment of overnutrition and sedentarism. 13 The other explanation Weiss provides for his view is that excess hypertension risk in African-derived peoples seems to him so “systematic, uniform and severe.” However, international comparative studies have demonstrated a broad range of hypertension prevalences and sequelae in populations of West African origin, spanning the range of all human populations. 14 Is it reasonable to characterize such phenotypic diversity as “systematic” or “uniform”? As for “severe,” there are several European populations with blood pressures just as high as or higher than those observed in African-Americans. 15,16 The argument for black exceptionalism in this regard is therefore without empiric foundation.

Of relatively minor consequence is the assertion by Weiss 3 that we fell into the common trap of referring to “African genes,” when this was a direct quote from the title of a Science News article and not our choice of words. 17 Weiss also took issue with our consideration of the role of peer review. Because the purpose of our essay was not to establish the truth or falsehood of the Slavery Hypothesis, but rather to question why anyone would invest much belief in it, the systematic avoidance of peer review on the part of the Hypothesis authors seemed to us a relevant point. Weiss disagreed, asserting that this was “an exceedingly weak argument” because so much “junk” makes it into the peer-reviewed literature. The salient issue, however, is not whether there is “junk” in the peer-reviewed literature, but whether there is a higher or lower concentration of “junk” in the non–peer reviewed literature.

In summary, the three commentaries present markedly different perspectives on the Slavery Hypothesis and our discussion of it. The views of Blackburn 1 are perhaps the most harmonious with our own, although he is apparently concerned by the tone of the debate and urges some modicum of tolerance between what he perceives as opposing world views. Grim and Robinson 2 dissent from our views, but counter only with speculations about biologic data they would like someday to see and a list of historical mortality estimates that do not appear in the sources they reference. They also complain that “accusations of racism [do not] belong in a scientific discussion,” although the words “racist” or “racism” appear nowhere in our essay. Finally, Weiss 3 argues on the basis of what could perhaps be true: the salt-sensitivity genotypes (if they existed) could have been favored, selection pressure during slavery could have been quite strong, and so forth. The issue at hand is whether or not there is any compelling reason actually to invest some substantial degree of belief in any of these speculations. Weiss concludes by disparaging our sociologic focus, but if no compelling rationale can be articulated for the Slavery Hypothesis, then the obvious next question is indeed sociologic: why do so many find the hypothesis worthy of receiving the benefit of the doubt?


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© 2003 Lippincott Williams & Wilkins, Inc.