The Great Physiologist of Heidelberg

Natural History, July, 1999 by Stephen Jay Gould

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Tiedemann's densely documented treatise announced a positive outcome for this grand hope of unification: the two sequences of human fetal development and comparative anatomy of brains from fish to mammals coincide perfectly. He wrote in triumph:

   I therefore publish here the research that I have done for several years on
   the brain of the [human] fetus.... I then present an exposition of the
   comparative anatomy of the structure of the brain in the four classes OF
   vertebrate animals [fish, reptiles, birds, and mammals, in his
   taxonomy]--all in order to prove that the formation of his organ in the
   [human] fetus, followed from month to month during its development, passes
   through the major stages of organization reached by the [vertebrate]
   animals in their complexity. We therefore cannot doubt that nature follows
   a uniform plan in the creation and development of the brain in both the
   human fetus and the sequence of vertebrate animals. (Author's translation
   from the 1823 French edition of Tiedemann's 1816 monograph)

Thus, Tiedemann had reached one of the most important and most widely cited conclusions of early-nineteenth-century zoology. Yet he never extended this notion, the proudest discovery of his life, to establish a .sequence of human races as well, although virtually all other scientists did. Nearly every major defense of conventional racial ranking in the nineteenth century expanded Tiedemann's argument from embryology and comparative anatomy to variation within a sequence of human races as well--by arguing that a supposedly linear order from African to Asian to European expresses the same universal law of progressive development.

Even the racial "liberals" of nineteenth-century biology invoked Tiedemann's linear sequence of progress when the doctrine suited their purposes. For example, as an argument for evolutionary intermediacy, T. H. Huxley proposed a linear order of races to fill the gap between apes and humans: "The difference in weight of brain between the highest and the lowest man is far greater, both relatively and absolutely, than that between the lowest man and the highest ape."

But Tiedemann himself, the inventor of the basic argument, would not extend his doctrine into a claim that variations within a species (distinctions among human races, in this case) must follow the same linear order as differences across related species. I can only assume that he demurred (as logic surely permits and as later research has confirmed, for variations within and among species represent quite different biological phenomena) because he did not wish to use his argument as a defense for racial ranking. At least we know that one of his eminent colleagues read his silence in exactly this light--for Richard Owen, refuting Huxley's claim, honored Tiedemann's conclusion when he penned the accolade used as a title to this essay:

   Although in most cases the Negro's brain is less than that of the European,
   I have observed individuals of the Negro race in whom the brain was as
   large as the average one of Caucasians; and I concur with the great
   physiologist of Heidelberg, who has recorded similar observations, in
   connecting with such cerebral development the fact that there has been no
   province of intellectual activity in which individuals of the pure Negro
   race have not distinguished themselves.

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The Great Physiologist of Heidelberg

Natural History, July, 1999 by Stephen Jay Gould

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