Leonardo’s Mountain of Clams and the Diet of Worms

by Stephen Jay Gould

  I will not rehearse the details of the hippocampus debate here, for no story in Victorian natural history has been told so often, and the basic facts are not in dispute. (My friend and colleague Charles G. Gross, professor of psychology at Princeton, has recently published a particularly clear and accessible article, notable for its focus on anatomical details of the brain—for Gross is a celebrated neurologist, not primarily a historian: “Hippocampus Minor and Man’s Place in Nature: A Case Study in the Social Construction of Neuroanatomy,” published in Hippocampus. Yes, in our world of specialization, each region of the brain has a journal devoted to its study!)

  The debate arose in the late 1850s and lasted with full force into the 1860s, sputtering out by the time Owen wrote his gorilla monograph in 1865. Owen and Huxley duked it out both in writing and in public appearances, notably at the same 1860 British Association meeting where, according to legend and unsupported by fact, Huxley also destroyed Bishop “Soapy Sam” Wilberforce in an initial altercation over Darwinism (the exchange took place, but without a clear victor). The debate spilled vigorously and copiously into general culture, as the public and press delighted in watching two of Britain’s greatest scientists acrimoniously debating such an important issue (the status of humans in nature) by wrangling about parts of the brain unknown to all and endowed with such wonderfully amusing names as “hippocampus minor.” Charles Kingsley, featuring the hippocampus debate in his 1863 children’s classic The Water Babies, emphasized the humor implicit in the conjunction of arcane anatomical mumbo-jumbo with a theme of such conceptual and emotional importance. Kingsley writes of Professor Ptthmllnsprts (Put-them-all-in-spirits), his parody of Huxley:

  He held very strange theories about a good many things. He had even got up once at the British Association, and declared that apes had hippopotamus majors in their brains just as men have. Which was a shocking thing to say; for, if it were so, what would become of the faith, hope, and charity of immortal millions? You may think that there are other more important differences between you and an ape, such as being able to speak, and make machines, and know right from wrong, and say your prayers, and other little matters of that kind; but that is a child’s fancy, my dear. Nothing is to be depended upon but the great hippopotamus test.

  On May 18, 1861, Punch published a quite accurate account of the issue in doggerel verse, beginning:

  Then Huxley and Owen

  With rivalry glowing,

  With pen and ink rush to the scratch:

  ’Tis Brain versus Brain,

  Till one of them’s slain;

  By Jove! it will be a good match!

  And indeed it was! Private letters give a good account of the animosity. Huxley wrote that he would “nail that mendacious humbug . . . like a kite to the barn door.” Owen described one of their public altercations to a friend: “Prof. Huxley disgraced the discussions by which scientific differences of opinion are rectified by imputing falsehood on a matter in which he differed from me. Until he retracts this imputation as publicly as he made it I must continue to believe that, in making it, he was merely imputing his own base and mendacious nature.”

  The “official” account of the debate can be summarized in a paragraph: Huxley approached the controversy like a military general, out to upstage an older enemy. He organized several colleagues to dissect the brains of various apes and monkeys in search of the structures that Owen had pronounced unique to humans. Huxley himself studied the brain of the South American spider monkey, a “lower” primate on the traditional scale. They also scoured published literature, searching both for Owen’s distortions or selective quotations, and for prior proof of the three structures in nonhuman primates. In short, they found abundant evidence for all three structures in various primates. Owen, according to legend, eventually shut up and licked his wounds.

  Owen’s tactics clearly led him to disaster. (Both Owen and Huxley came from lower middle-class backgrounds, but Owen had ingratiated himself into upper circles, to his enormous practical benefit, receiving a rent-free residence directly from Queen Victoria and, beginning in the early 1840s, an annual civil list pension, all achieved while Huxley struggled financially and grew bitterly jealous. Never doubt the centrality of social class for understanding Victorian life.) As a nouveau arrivé in the upper classes, Owen felt that he had to obey perceived norms for imperious disregard of upstarts. He fought for his positions, and against Huxley, but not with the same vigor, and with none of Huxley’s overt organization. Owen largely tut-tutted among his noble friends, and lost precious ground.

  Owen’s tactics evidently failed, but were his arguments so bad? I will not attempt to deny the usual reading—that Huxley and his phalanx found all three structures in the brains of nonhuman primates, therefore disproving Owen’s criteria of uniqueness. But was Owen really so stupid, and so defeated? I don’t think so. I would like to raise two points for balance, and partly in Owen’s defense—the first well discussed by Rupke and others, the second (so far as I know) not previously covered in the literature.

  First, how did Owen respond to Huxley and company’s discovery of the three structures in apes and monkeys? Did he just deny their findings, or suffer in silence? In fact, Owen made a potentially fair reply. He had been stating for years (though he had conveniently omitted the claim in several publications at the height of the hippocampus debate) that virtually every feature of humans has a homologous expression in closely related chimps and gorillas. (Owen had coined the term homology in the late 1840s to identify features of identical anatomical origin in different creatures, whatever the degree of functional divergence—wings of bats with front legs of horses, for example. We now attribute homology to evolutionary descent from a common ancestor.) But admission of homology does not require application of the same name to the relevant feature in two organisms, for functional divergence might legitimately permit a different term. For example, calling the bat’s forearm a wing doesn’t obligate us to state that all mammals have wings because all carry homologs of the bat’s forearm bones.

  Owen invoked a sneaky version of this purely terminological point to worm out of his defeat—but we must at least credit the technical validity of his claim. In the 1865 gorilla monograph, he admits that the three structures do exist in apes, but in such rudimentary state, and in such different form from their expression in humans, that all must receive a different name—just as horses don’t have wings. Thus, we can still say that apes don’t have a posterior lobe, a posterior cornu, and a hippocampus minor—even though they possess homologs of all these human structures!

  Owen begins by allowing pervasive homology: “In the Gorilla . . . the homologue of every organ and of almost every named part in Human anatomy is present.” He then discusses how a gorilla brain might be topologically transformed to a human brain, almost nonchalantly admitting at the end that the three structures already exist in gorillas!

  . . . to expand the cerebrum in all directions, and especially backward beyond the cerebellum, so as to define a “posterior” or “post cerebellar” lobe: to extend the chief cerebral cavity, or “lateral ventricle” . . . backward . . . into a “posterior horn” . . . with prominences corresponding with . . . the “hippocampus minor”; the beginnings or incipient homologues of which cavity and part are alone present in the highest Apes.

  I could accept Owen’s redefinition as clever and honorable, but for two points. First, he implies that he doesn’t have to give the same name to the three features in apes because they are so poorly developed. But Huxley and colleagues had shown that some apes develop these features to equal strength with their expression in humans. Second, if Owen had taken this position all along, then we could blame Huxley for unsubtlety. But, in fact, Owen didn’t begin by admitting rudimentary homologs of the three features in apes, and merely claiming that strong human development required a separate name. He really did deny that the structures existed at all in apes. Owen wrote in his 1859 lecture:

  Posterior
development [of the cerebrum] is so marked that anthropotomists have assigned to that part the character and name of a “third lobe”; it is peculiar and common to the genus Homo: equally peculiar is the “posterior horn of the lateral ventricle” and the “hippocampus minor,” which characterize the hind lobe of each hemisphere. Peculiar mental powers are associated with this highest form of brain . . . I am led to regard the genus Homo as not merely a representative of a distinct order, but of a distinct subclass, of the Mammalia.

  I do think, particularly in this context of focal conclusion, that “peculiar” means “unique”—and that Owen did shift his ground by verbal ploy, thus illustrating the valid part of Huxley’s mistrust and anger.

  But the second point, previously overlooked in our large literature, does corroborate an important part of Owen’s argument—one with wrenching implications in our current reality. Huxley was clearly right in demonstrating the three structures in other apes, but his central presentation of the argument for evolutionary continuity between apes and humans, published most prominently in Man’s Place in Nature (1863), rests upon two false arguments (one as sneaky as Owen’s later attempt to cover his ass), and both well refuted by Owen in his gorilla monograph of 1865.

  Man’s Place in Nature presents the strongest defensible version of smooth evolutionary transition between apes and humans. Huxley admits the undeniable gap in brain size, with smaller-bodied humans carrying a brain three times as large as that of much weightier gorillas, but correctly identifies this disparity as a gulf in quantity alone, for all parts of the brain are homologous in apes and humans. Huxley then, and with equal justice, argues that a different quantity of brain need not account for a true gulf in quality of mental operations, for such a claim would confuse correlation with causality. Perhaps, Huxley states, human cognitive superiority resides in some unidentified difference of cellular or microarchitectural function, and not in disparity of bulk alone.

  Huxley then presents his two linked arguments. First, he hammers home by brute force, listing feature after feature, his key claim for continuity: the gap between the lowest ape and the chimp or gorilla is far greater than the corresponding gap between these “highest” apes and humans—so we are just one small step farther along in the sequence of apes:

  Whatever part of the animal fabric—whatever series of muscles, whatever viscera might be selected for comparison—the result would be the same—the lower Apes and the Gorilla would differ more than the Gorilla and the Man . . . The structural differences between Man and the highest Apes are of less value than those between the highest and the lower Apes.

  But Huxley’s argument seems unfair and even a tad self-serving within the context that both he and Owen shared: a belief that groups of related organisms should be ranked on a scale from lower to higher. (Our current denial of this scheme is, of course, irrelevant to our analysis of the logical structure of Huxley and Owen’s arguments.) Owen properly refuted Huxley by pointing out that he had made a false comparison of disparate things—apples and oranges in the current cliché. The gap between gorilla and human amounts to one step, but the separation of “lower” primates from chimps and gorillas encompasses scores of omitted intermediates. If I were trying to minimize the gap between step 50 and 51 in a series by arguing that the separation between step 1 and step 50 is even greater, you would properly laugh me to scorn and say, “Don’t load the dice inevitably in your favor; compare the right things. Tell me about the gap between 49 and 50 versus 50 and 51. A step must be compared with a step, not with the entire series!” If the gorilla-human step exceeds the distance between any two adjacent primates, then I may regard humans as something special. Owen writes:

  Passing . . . to a comparison of the Gorilla’s brain with that of other Quadrumana [apes], we discern the importance and significance of the much greater difference between the highest Ape and lowest Man, than exists between any two genera of Quadrumana in this respect . . . From [gorillas] to Lemurs [the “lowest” primate in Owen’s scheme] the difference of cerebral development shown in any step of the descensive series is insignificant compared with the great and abrupt rise in cerebral development met with in comparing the brain of the Gorilla with that of the lowest of the Human races.

  I think that Huxley sensed the weakness of his argument, for he introduced a second supposed clincher in conjunction and support: the gap between gorilla and average human may be large, but if we order all human variation in a hierarchical ranking of races, from the “lowest” Negro to the “highest” Caucasian, then the gap closes, for the step from gorilla to lowest human becomes less than the space between lowest and highest Homo sapiens. (Please understand that I am using Huxley’s own terms and quoting the conventional wisdom of his day within the restricted community of scientists—that is, white males of privilege.) Huxley wrote:

  The difference in weight of brain between the highest and the lowest men is far greater, both relatively and absolutely, than that between the lowest man and the highest ape . . . Thus, even in the important matter of cranial capacity, Men differ more widely from one another than they do from the Apes.

  I do not think that Huxley, a racial liberal by the standards of his time, advanced this argument with intent to impugn entire groups of human beings. Rather, he was trying to plug a hole in his central argument for evolutionary continuity by finding some way to fill the embarrassingly large space in cranial capacity between gorilla and average human.

  This complex world of ours, this vale of tears, lies awash in irony. Just as bad things happen to good people, decent folks also advance logically fallacious and morally dubious claims in support of good arguments. Huxley stood on the side of the angels: he tried to advance the cause of human evolution by documenting continuity with our closest animal relatives. He closed his case with a magnificent prose flourish in describing the great range of design within the primate order, from the lowest lemur to our exalted selves:

  Perhaps no order of mammals presents us with so extraordinary a series of gradations as this—leading us insensibly from the crown and summit of the animal creation down to creatures, from which there is but a step, as it seems, to the lowest, smallest, and least intelligent of the placental Mammalia. It is as if nature herself had foreseen the arrogance of man, and with Roman severity had provided that his intellect, by its very triumphs, should call into prominence the slaves, admonishing the conqueror that he is but dust.

  Nonetheless, and whatever his broader good intent, Huxley did advance in support a harsh, uncompromising, and undeniably racist argument that arranged all humans in a line of advancing worth, and explicitly identified African blacks as midway at best between gorillas and European whites. Huxley’s error arose from a deep fallacy in his evolutionary reasoning—the progressivist equation of evolution with linear advance. He assumed that evolution must proceed in a series of rising steps, and he felt that he couldn’t defend human evolution unless he could demonstrate such a linear order among modern people. In this assumption, he committed an even deeper error based on a classically false premise of reasoning: belief in continuity of cause, with failure to recognize that superficially similar phenomena at different scales may have disparate causes.

  Yes, humans differ from apes and, yes, humans vary among themselves. But these facts don’t imply that variation among modern humans acts as a microcosm for larger differences between humans and other species—though Huxley assumed such continuity when he ran human racial variation along the same scale as differences among primate species. Human races are not surrogates for intermediate steps between ancestral apes and modern people; human races represent an entirely different scale of contemporary variation within a single biological species. We have no reason either to rank variation within a species along any line of worth, or to regard such contemporary diversity as particularly related to modes of our evolutionary derivation. Of course, evolution does predict that the gap between ancestral apes and modern humans must be bridgeable, but the
transitional forms are extinct species of the fossil record, not modern races. Moreover, since modern races are so young (as we now know), our differences are effectively inconsequential in evolutionary terms. No human race is, in toto, more apelike than any other. We are all recently derived varieties of the common human stock, Homo sapiens.

  Poor, maligned, politically conservative, intellectually antediluvian Richard Owen. He took one look at Huxley’s racist argument, and nailed him—like a kite to the barn door, and exactly for the right reasons. I know that Owen did not refute Huxley in the service of racial egalitarianism. I know that Owen shared all Huxley’s prejudices about racial ranking and the existence of higher and lower forms of human life. Owen’s text is sprinkled with the conventional language of a shared racist perspective. In 1859 he wrote that the chimpanzee lies “nearer than any other known mammalian animal to the human species, particularly to the lower, or Negro forms.” And later in the same work: “In the low, uneducated, uncivilized races, the brain is rather smaller than in the higher, more civilized and educated races.” In the 1865 gorilla monograph, he rolls all common prejudices into one line by stating that male skulls must be treated as standards, with both females and lower races (identified, conventionally, as Ethiopian, or African black, and Papuan, or Melanesian black) as inferior: “If the naturalist . . . were to abandon his proper guide, viz. the average condition of the brain in the male sex, and to take the brain of a female of the lowest Papuan or Ethiopian variety . . .”

  I also know that Owen refuted Huxley’s racist argument in order to defend human uniqueness against a claim for continuity, and not for any social or political motive that we might honor today. Nonetheless, intentions and consequences must be separated (and much of the fascinating complexity and moral ambiguity in our lives arises from the sharp disparity so often encountered between our goals and the opposite, yet unavoidable, side consequences of actions taken in the service of these goals—oppose hunting on principle, and too many deer may eat your flower gardens). Thus, I applaud the consequence of Owen’s argument, whatever his intent.