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No More "Slavery Hypothesis" Yarns

Department of Epidemiology, University of North Carolina School of Public Health, Chapel Hill, North Carolina

Dr. Dimsdale’s (1) otherwise thoughtful and illuminating discussion of ethnicity and health was marred by his careless repetition of the old "Slavery Hypothesis" yarn. He suggests that the historical "data" are "suggestive of a genetic legacy from the Middle Passage," helping to account for the excess burden of hypertension currently found in North American populations of African descent.

What exactly are these historical data that are brought to bear on this question? The author cites four pieces of evidence: 1) overall mortality in the Middle Passage averaged 30%; 2) this mortality resulted primarily from dehydration secondary to excess heat and diarrheal illness; 3) according to Herman Melville, sharks followed slave ships across the Atlantic; and 4) an 18th century engraving purportedly shows an English trader licking the cheek of an African captive "to taste his sweat before boarding the ship."

We can immediately discount the latter two items as irrelevant anecdotes. If we were to accept artistic representations uncritically as literal accounts, we would also have to conclude that winged cherubs hovered over Renaissance Europe and that dogs play poker. This leaves only two arguments to support the author’s assertion of a "genetic legacy" from the trans-Atlantic journey relevant to contemporary hypertension risk: that overall mortality during the Middle Passage averaged 30% and that most deaths were due to dehydration. Neither is even approximately accurate.

The cited source of the 30% average mortality figure is a book that is directed to a popular rather than a scholarly audience and therefore lacks detailed referencing of its sources. Current scholarship on the slave trade, including newly compiled computerized records from 27,233 trans-Atlantic slave ship voyages made between 1595 and 1866, allows for more valid mortality estimates (2). Mortality of Africans in the Middle Passage was highest before 1700, averaging about 20%. By the mid-1700s the mean stood at about 10%, and by the last quarter of the 18th century mortality during Atlantic transit averaged around 5%. Because roughly 80% of the total number of African slaves delivered to the New World were landed between 1700 and 1850, the overall mortality level averaged about 13% (3). This is in no way intended to suggest that the conditions of the Middle Passage were any less horrific. My point is simply to urge that quantitative historical arguments in scientific discourse be made with the same care and standards of evidence as we would expect from biomedical research.

That the specific cause of these deaths was largely secondary to dehydration has already been refuted by historians of the slave trade (4, 5). In fact, the "Slavery Hypothesis" has been rejected as incompatible not only with historical data but also with principles of population genetics (6). The essay in Psychosomatic Medicine has unwittingly perpetuated this old pseudoscientific canard, which plays into the hands of racial essentialists and biological determinists. The seductive nature of Dr. Grim’s fairytale is itself an interesting sociological phenomenon. We may wonder why, despite an absolute lack of supporting evidence, in fact a great weight of contradictory evidence, otherwise smart and reasonable people continue to rehash this fantasy as though it were sensible and respectable science.

REFERENCES

1. Dimsdale JE. Stalked by the past: the influence of ethnicity on health. Psychosom Med 2000; 62: 161–70.[Abstract/Free Full Text]
2. Eltis D, Behrendt SD, Richardson D, Klein HS, editors. The trans-Atlantic slave trade: a database on CD-ROM. Cambridge, UK: Cambridge University Press; 1999.
3. Klein HS. The Atlantic slave trade. Cambridge, UK: Cambridge University Press; 1999.
4. Steckel R, Jensen A. New evidence on the causes of slave and crew mortality in the Atlantic slave trade. J Econ Hist 1986; 46: 57–77.[Medline]
5. Curtin PD. The slavery hypothesis for hypertension among African Americans: the historical evidence. Am J Public Health 1992; 82: 1681–6.[Abstract/Free Full Text]
6. Jackson FL. An evolutionary perspective on salt, hypertension, and human genetic variability. Hypertension 1991; 17 (1 Suppl): I-129–32.

Response

Editor-in-Chief, Psychosomatic Medicine, Department of Psychiatry, University of California, San Diego, La Jolla, California

In my article (1), I argue for the importance of considering the effects of race and ethnicity on health. I acknowledged that there is passionate debate on this topic and made a plea for reasoned discourse. Professor Kaufman (2) takes umbrage with one part of the discussion concerning whether the Atlantic slave trade had long-term health reverberations. The argument proposes that the experience not only seared the consciousness of the slaves and their descendents but also that it may have left a genetic legacy. Let me respond to his points.

1. Kaufman criticizes my mortality estimates from the Middle Passage, implying that my source (3), historian Hugh Thomas, is not a reputable scholar. Thomas is an eminent historian whose scholarship, according to Kaufman, should be discounted because his books are widely read, a curious indictment. Kaufman also alleges that Thomas does not provide careful citation of sources. The Thomas book consists of roughly 800 pages of text plus about 60 additional pages of references, notes, and appendices, hardly what I would call insufficiently referenced. Kaufman prefers work by Eltis et al. (4), whom he suggests conclusively established considerably lower mortality rates during the Middle Passage. I agree that the Eltis et al. database is a rich one; however, my understanding of the work differs from what Kaufman suggests. I am not impugning Eltis et al.’s database but rather pointing out its limitations, which Kaufman neglected to mention. Eltis et al. (but not Kaufman) acknowledge the complexity and uncertainty of this area. They state that their data represents approximately two-thirds of the slaving voyages. Second, their database contains information on Middle Passage mortality for only 5130 voyages of their 27,233-voyage data set. Third, they imputed the death rates because of the limitations of their records. In other words, the exact mortality rates on the Middle Passage are uncertain to everyone. Whose scholarship is more "reliable," mine and Thomas’ or Kaufman’s incomplete citation from Eltis et al.’s work, is a debatable proposition.

2. Kaufman was unhappy that I referred to contemporary observers of the slave trade, specifically to Melville’s description of sharks following slave ships and to artists’ depictions of slave selection. Kaufman dismisses these sources as invalid because other artists have drawn things such as dogs playing cards. He sets himself up as an arbiter of what constitutes acceptable truth or evidence. If he wishes to dismiss my sources, he has that right, but I suspect that most readers would find these sources worthy of consideration.

3. Kaufman disputes my statement that dehydration, heat, diarrheal illness, and electrolyte disturbances played a major role in cause of deaths in transit. There must be a misunderstanding here because most scholars agree on these points. Indeed, one of Kaufman’s sources, Steckel and Jensen (5), states that gastrointestinal disturbances were responsible for the greatest annual death rates in slaves during Middle Passage transit.

4. Kaufman suggests that I was benighted in referring to Clarence Grim’s "Slavery Hypothesis." He calls this "a canard," a hoax, and suggests that right-thinking (or is it left-thinking?) people have long since disproved it. My article stated that Grim’s hypothesis is "sheer speculation ... difficult to evaluate from the distance of time." To brand it as a hoax seems excessive. Grim is a prominent hypertension researcher. In science we test hypotheses rather than stamp out heresy. Kaufman suggests that Grim’s hypothesis and my referring to it appeal to "racial essentialists and biological determinists." I do not accept that characterization; it sounds like name calling and politicized slogans.

Let me restate my proposition. Race and ethnicity are too important to be ignored or politicized. Phenotype reflects both genotype and personal/cultural life experience. Kaufman clearly shares my first premise, the importance of considering race and ethnicity. To my way of thinking, however, he is too full of passionate intensity and ideological conviction that he knows "the truth." Galileo stated the problem of contentious science quite clearly (as quoted in Ref. 6) when he said, "... we must be content with what little we may conjecture here among shadows... ."

REFERENCES

1. Dimsdale JE. Stalked by the past: the influence of ethnicity on health. Psychosom Med 2000; 62: 161–70.
2. Kaufman J. No more "slavery hypothesis" yarns [letter]. Psychosom Med 2001; 63: 324.[Free Full Text]
3. Thomas H. The slave trade. the story of the Atlantic slave trade: 1440–1870. New York: Simon & Schuster; 1997.
4. Eltis D, Behrendt S, Richardson D, Klein H. The trans-Atlantic slave trade: a database on CD-ROM. Cambridge, UK: Cambridge University Press; 1999.
5. Steckel R, Jensen A. New evidence on the causes of slave and crew mortality in the Atlantic slave trade. J Econ Hist 1986; 46: 57–77.
6. Sobel D. Gallileo’s daughter. New York: Walker & Company; 1999. p. 91.

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