Stephen Jay Gould
(10.9.1941 - 20.5.2002)
Stephen Jay Gould
The Structure of Evolutionary Theory
Darwin as a Philosophical Revolutionary
THE CAUSES OF NATURE'S HARMONY
Darwin and William Paley
In November 1859, just a week before the official publication date of
the Origin, Darwin wrote to his neighbor John Lubbock* "I do not
think I hardly ever admired a book more than Paley's 'Natural Theology.'
I could almost formerly have said it by heart" (in F. Darwin, 1887, volume
2, p. 219).
The Reverend James McCosh receives my vote for the most interesting among a largely forgotten group of late 19th century thinkers who played a vital role in their own time-liberal theologians friendly to evolution (though not usually to Darwin's philosophy), and who prove that if any warring camps can be designated in this realm, the combatants surely cannot be la- beled as science vs. religion (see Gould, 1999b), but rather as expressions of a much deeper struggle between tradition and reform, or dogmatics and openness to change. McCosh doesn't even merit a line in the Encyclopedia Britannica, though he did serve as president of Princeton University, where he had a major influence on the career of Henry Fairfield Osborn and other important American evolutionists.
In 1851, McCosh published an article entitled "Typical Forms" in the North British Review. Hugh Miller, the self-taught Scottish geologist and general thinker, called this article "at once the most suggestive and ingenious which we have almost ever perused," and urged McCosh to expand his argument to an entire volume. McCosh accepted this advice and, in collaboration with George Dickie, published Typical Forms and Species Ends in Creation in 1869. The Greek inscription on the title page - typos kai telos (type and purpose) - epitomizes the argument. McCosh holds that Goïs order and benevolence may be inferred from two almost contradictory properties that reside in tension within all natural objects - "the principle of order" and "the principle of special adaptation." (These two principles persist in Darwin's formulation under the names "Unity of Type" and "Conditions of Existence" - 1859, p. 206, for example (see my extensive treatment of this passage on pp. 251-260), where their fundamental character merits upper case designations from Darwin.) McCosh defines his first principle as "a general plan, pattern, or type, to which every given object is made to conform"; and his second as a "particular end, by which each object, while constructed after a general model is, at the same time, accommodated to the situation which it has to occupy, and a purpose which it is intended to serve" (1869, p. 1). (If we call these two principles "anatomical ground plan" and "adaptation" we will be able to make the appropriate evolutionary translation without difficulty.)
*Later Lord Avebury and an author of many fine evolutionary works himself. But Lub- bock's greatest contribution to human thought was probably indirect, a result of neighborly fellowship - for he sold to Darwin a corner of property that became the famous "sandwalk" where Darwin, perambulating and kicking aside a flint cobble for each circumnavigation, solved several riddles of life and human existence. Darwin graded the difficulty of his problems by the number of circuits required for solution-two-flint problems, five-flint problems, etc. I suspect that macroevolutionary theory must present us with at least a fifty-flint problem!
McCosh argues that Goïs existence and benevolence can be inferred from
either principle-from the first by the order of taxonomy, and the abstract
beauty of hodily symmetry and structure; and from the second, by "adaptation,"*
or the exquisite fit of form to function. McCosh also notes that the second,
or functional, argument constitutes the "national signature" of Brit- ish
thought: "The arguments and illustrations adduced by British writers for
the last age or two in behalf of the Divine existence, have been taken
almost exclusively from the indications in nature of special adaptation
of parts" (1869, p. 6).
The main lineage of this national tradition for "natural theology" based on the "argument from design" runs from Robert Boyle's Disquisition About the Final Causes of Natural Things (1688) and John Ray's Wisdom of God Manifested in the Works of the Creation (1691) in Newton's generation that promulgated what historians call "the scientific revolution"; to a grand culmination in William Paley's Natural Theology (1802), one of the most influential books of the 19th century; to an anticlimax, during the 1830's, in the eight "Bridgewater Treatises" (including volumes by Buckland and Whewell), established by a legacy from the deceased Earl of Bridgewater for a series of volumes "on the power, wisdom, and goodness of God, as manifested in the creation." Critics in Darwin's circle generally referred to this series as the "bilgewater treatises."
Revolutions usually begin as replacements for older certainties, and not as pristine discoveries in uncharted terrain. In understanding the second pole of Darwin's genius as the uncompromising radicalism of his new philosophy for life and history, we must first characterize the comfortable orthodoxy uprooted by the theory of natural selection. Darwin's essential argument begins with a definition of the dominant philosophy for natural history in his day - natural theology in the Paleyan mode.
*The word adaptation did not enter biology with the advent of evolutionary theory. The Oxford English Dictionary traces this term to the early 17th century in a variety of meanings, all designating the design or suitability of an object for a particular function, the fit of one thing to another. The British school of natural theology used "adaptation" as a standard word for illustrating Goïs wisdom by the exquisite fit of form to immediate function. Darwin, in borrowing this term, followed an established definition while radically revising the cause of the phenomenon.
At the outset of Chapter 4, I will say more about Paley and the alternative
vision of continental natural theology (adaptationism vs. laws of form).
For now, a simple statement of the two chief precepts of Paleyan biology
NATURAL THEOLOGY IN GENERAL. The rational and harmonious construction of nature displays the character and benevolence of a creating God. In the last four chapters of his book, Paley tells us what we may infer about God from the works of creation. Goïs existence, of course, shines forth in his works, but this we know from many other sources. More specifically (and with a Paleyan chapter for each), nature instructs us about Goïs personality, his natural attributes, his unity, and (above all) his goodness.
PALEY'S PARTICULAR VERSION OF NATURAL THEOLOGY. Natural theology has been expressed in two basic modes (see Chapter 4), one primarily continental (laws of form), the other mainly British (adaptationism). Paley held that God manifests his creating power in the exquisite design of organisms for their immediate function. We all know Paley's famous opening metaphor: if I find a watch lying abandoned on an open field, I can conclude from the complex set of parts, all shaped to a common purpose and all well designed for a specific end, that some higher intelligence constructed the watch both directly and for a particular use. Since organisms show even more complexity and even more exquisite design, they must have been fashioned by an even greater intelligence. But fewer biologists know Paley's more specific argument against the alternative version of natural theology (laws of form), as presented in his chapter 15 on "relations." The parts of organisms exist in concert not because laws of form or symmetry demand one feature to balance another, but "from the relation which the parts bear to one another in the prosecution of a common purpose" (1803 edition, p. 296) - that is, to secure an optimal adaptation of the whole.
At the very outset of the Origin, Darwin tells us that his explanation of evolution will stress the Paleyan problem of exquisite adaptation. He writes, in the Introduction, that we could obtain sufficient confidence about evolution by "reflecting on the mutual affinities of organic beings, on their embryological relations, their geographical distribution, geological succession, and other such facts" (1859', p. 3). "Nevertheless," he continues, "such a conclusion, even if well founded, would be unsatisfactory, until it could be shown how the innumerable species inhabiting this world have been modified, so as to acquire that perfection of structure and coadaptation which most justly excites our admiration" (1859, p. 3). The explanation of adaptation therefore stands forth as the primary problem of evolution. Many lines of evidence prove that evolution occurred. But if we wish to learn how evolution works, we must study adaptation.
This basic Darwinian argument operates as a close copy of Paley's defense, recast in evolutionary language, for the English alternative in natural theology. We can infer, Paley often states, that God exists from innumerable aspects of nature. But if we wish to know any more about the creator - his nature, his attributes, his intentions - we must study the excellence of adaptation via the "argument from design." Paley writes (1803, p. 60): "When we are enquiring simply after the existence of an intelligent Creator, imperfection, inaccuracy, liability to disorder, occasional irregularities, may subsist, in a considerable degree, without inducing any doubt into the question."
On the other band, adaptation in the fashioning of contrivances for definite ends reveals Goïs nature. Paley invokes this theme as a litany in developing his initial parable of the watch and watchmaker. He cites other possible explanations for the origin of the watch, and then intones, after each: "Contrivance is stilI unaccounted for. We stilI want a contriver" ("want," that is, in the old sense of "lack," not the modern "desire" - p. 13). "Contrivance must have had a contriver, design, a designer" (p. 14). Later, he tells us explicitly that nature can testify to Goïs character and goodness only by the phenomenon of adaptation (pp. 42-43): "It is only by the display of contrivance, that the existence, the agency, the wisdom of the Deity, could be testified to his rational creatures. This is the scale by which we ascend to all the knowledge of our Creator which we possess, so far as it depends upon the phenomena, or the works of nature... It is in the construction of instruments, in the choice and adaptation of means, that a creative intelIigence is seen. It is this which constitutes the order and the beauty of the universe."
I had never read Natural Theology straight through before pursuing my research for this book. In so doing, I was struck by the correspondences between Paley's and Darwin's structure of argument (though Darwin, of course, inverts the explanation). Darwin did not exaggerate when stating to Lubbock that he had virtually committed Paley to memory. The style of Darwin's arguments, his choice of examples, even his rhythms and words, must often reflect (perhaps unconsciously) his memory of Paley. Consider just a few examples of this crucial linkage:
1. Paley, like Darwin, relies upon comparison and extrapolation from artificial to natural. Darwin moves from artificial to natural selection, Paley from human to animal machines. Both rely on the central argument that a common mechanism works much more powerfully in nature. Paley's words recall Darwin's argument that natural selection, working on all parts for so much time, must trump artificial selection, which only affects the few features we choose to emphasize in the short duration of human history. "For every indication of contrivance, every manifestation of design, which existed in the watch, exists in the works of nature; with the difference, on the side of nature, of being greater and more, and that in a degree which exceeds all computation" (1803, p. 19).
2. Both men invoke the same examples. Paley compares the eye and telescope; Darwin lauds the eye as the finest example of complex natural design, and then presents an evolutionary explanation. Paley cites the swimbladder as an independent device created for life in water; Darwin ilIustrates homology with the tetrapod lung and proposes an evolutionary passage.
3. Darwin often uses Paley's logic, sometimes against his predecessor. Paley, for example, dismisses arguments about "tendencies to order" or "principles of design" as empty verbiage, explaining nothing; a true cause must be identified, namely God himself. Darwin makes the same point, but cites evolution as the true cause, while branding statements about creation ex nihilo as empty verbiage. Paley writes (p. 76): "A principle of order is the word: but what is meant by a principle of order, as different from an intelligent Creator, has not been explained either by definition or example: and, without such explanation, it should seem to be a mere substitution of words for reasons, names for causes."
4. Paley discusses many themes of later and central importance to Darwin. He criticizes the major evolutionary conjectures of his day, including Buffon on "interior molds," and the idea of use and disuse. (Since I doubt that he had read Lamarck's earliest evolutionary work by 1802, Paley probably derived this aspect of Lamarck's theory from its status as folk wisdom in general culture.) Paley also states the following crisp epitome of the very argument from Malthus that so struck Darwin. (I am not claiming that this passage provided a covert source for Darwin's central insight. Darwin, after all, had also read Malthus.) "The order of generation proceeds by something like a geometrical progression. The increase of provision, under circumstances even the most advantageous, can only assume the form on an arithmetic series. Whence it follows, that the population will always overtake the provision, will pass beyond the line of plenty, and will continue to increase till checked by the difficulty of procuring subsistence" (p. 540).
This influence, and this desire to overturn Paley, persisted throughout Darwin's career. Ghiselin (1969), for example, regards Darwin's orchid book as a conscious satire on Paley's terminology and argument. Darwin called this work (1862), his next book after the Origin of Species, "On the various contrivances by which British and foreign orchids are fertilized by insects." Paley used the word "contrivance," as my previous quotations show, to designate an organic design obviously well-made by an intelligent designer. But Darwin argues that orchids must be explained as contraptions, not contrivances. Their vaunted adaptations are jury-rigged from ordinary parts of flowers, and must have evolved from such an ancestral source; the major adaptive features of orchids have not been expressly and uniquely designed for their current functions.
Now suppose, as a problem in abstract perversity, that one made a pledge to subvert Paley in the most radical way possible. What would one claim? I can imagine two basic refutations. One might label Paley's primary observation as simply wrong - by arguing that exquisite adaptation is relatively rare, and that the world is replete with error, imperfection, misery and caprice. If God made such a world, then we might want to reassess our decision to worship him. An upsetting argument indeed, but Darwin chose an even more radical alternative.
With even more perversity, one might judge Paley's observation as undoubtedly correct. Nature features exquisite adaptation at overwhelming relative frequency. But the unkindest cut of all then holds that this order, the very basis of Paley's inference about the nature of God, arises not directly from omnipotent benevolence, but only as a side-consequence of a causal principle of entirely opposite import - namely, as the incidental effect of organisms struggling for their own benefit, expressed as reproductive success. Could any argument be more subversive? One accepts the conventional observation, but then offers an explanation that not only inverts orthodoxy, but seems to mock the standard interpretation in a manner that could almost be called cruel. This more radical version lies at the core of Darwin's argument for natural selection. (Darwin actually employed both versions of the radical argument against Paley, but for different aspects of his full case. He invoked oddities and imperfections as his major evidence for the factuality of evolution (see pp. 111-116). But he used the more radical version - exquisite adaptation exists in abundance, but its cause inverts Paley's world - to construct his mechanism for evolutionary change, the theory of natural selection.)
We all understand, of course, that the force of Darwin's radicalism extends well beyond the inversion of an explanatory order; he also undercut a primary source of human comfort and solace. This book cannot address such a vital issue at any depth, but I must record the point -for this wrenching became so salient in subsequent human history. If the natural footprints of Paley's God - the source of our confidence in his character, his goodness and, incidentally, the only hint from nature that we should accept other revealed doctrines, in particular the idea of bodily resurrection (1803, pp. 580-581) - must be reconceived as epiphenomena of a struggle for personal success, then what becomes of nature's beauty, instruction and solace? What a bitter cup Darwin offers us, compared with Paley's sweet promise (1803, pp. 578-579): "The hinges in the wings of an earwig, and the joints of its antennae, are as highly wrought, as if the Creator had had nothing else to finish. We see no signs of diminution of care by multiplication of objects, or of distraction of thought by variety. We have no reason to fear, therefore, our being forgotten, or overlooked, or neglected."
But then, the man who served as the primary focus of Paley's veneration had also promised that the truth would make us free; and Darwin justly argued that nature cannot provide the source of morality or comfort in any case.
see my selected bibliography of Stephen jay Gould