But Whitman had an even bolder vision, based on the same orthogenetic pattern. He did not interpret the pathway from checkers to bars as a circumscribed peculiarity of domestic pigeons, but rather as part of a much more extensive orthogenetic trend pervading the entire pigeon family (including all other species from mourning dove to passenger pigeon, which became extinct in the decade between Whitman’s death and the posthumous publication of his monograph), and perhaps even all coloration in birds—an inherent and ineluctable progression from an original homogeneous checkering on all feathers; to the concentration of color in certain areas (checkers plus bars, and then to bars alone); to the reduction and weakening of these concentrations; to the final elimination of all color. Whitman located the ancestral state in the uniform checkering of some species—the “turtle dove pattern” in his terminology (see figure)—and the final goal in some idealized, albinized version of the Holy Ghost, depicted as a pure white dove in so many medieval paintings: in short, and in his words, from uniform spotting to “immaculate monochrome”—a most unpigeonlike state (in both appearance and deed), at least in our metaphors. In a remarkable vision of inexorable movement through the entire great family of pigeons, Whitman writes:
When we look around among allied species and see the same bars reduced to about half dimensions in the rock pigeon of Manchuria, reduced to mere remnants of two to six spots in the stock dove, carried to complete obsoletion [sic] or to a few shadowy reminiscences in…Columba rufina of Brasil, gone past return in some of our domestic breeds and in many of the wild [doves and pigeons]—when we see all these stages multiplied and varied through some 400 to 500 wild species and 100 to 200 domestic breeds, and in general tending to the same goal, we begin to realize that they are…slowly passing phases in the progress of an orthogenetic process of evolution, which seems to have no fixed goal this side of an immaculate monochrome—possibly none short of complete albinism.
The fully checkered turtledove pattern, which Whitman regarded as the original state in his orthogenetic sequence. Courtesy of Department of Library Services, American Museum of Natural History.
Moreover, while the progress of the trend may be “lengthened or shortened, strengthened or weakened” by such subsidiary forces as natural selection, the orthogenetic sequence is invariable: “The steps are seriated in a causal, genetic order—an order that admits no transpositions, no reversals, no mutational skips, no unpredictable chance intrusions.” When we discern the proper sequence of orthogenetic stages, evolution may become a predictive science: “Not only is the direction of the change hitherto discoverable, but its future course is predictable.”
I have not resurrected Whitman’s largely forgotten work in order to defend orthogenesis as a replacement for natural selection, for this is truly a dead issue decided long ago in Darwin’s favor. Rather, from my deep admiration of Whitman’s keen intelligence and my abiding respect for his decades of careful work with pigeons, I wish to point out that his conclusions were not foolish, and that several aspects of his work would repay our close study, even today. Consider three points that might prompt a proper sympathy and interest.
1. The false charge of teleology. The standard one-liners of evolution texts dismiss orthogenesis as a theistically inspired last-gasp effort to salvage some form of inherent goal and purpose in Darwin’s new world. In this canard, supporters of orthogenesis abandoned rationality itself to embrace a woolly mysticism of “vital forces” and “inherent directions”—the very concepts that science had struggled to discard in field after field, from cosmology to physics to chemistry. Whitman has been viewed as a particularly sad example of this slippage and surrender, for he had been such a committed mechanist in his earlier embryological work.
This hurtful charge is not only wrong, but entirely backwards. Whitman and nearly all other prominent supporters of orthogenesis maintained as firm a commitment to mechanical causation, and as strong an aversion to mystical or spiritual direction, as any contemporary in this late-nineteenth-century age of industrial order. In the opening paragraph of his 1919 monograph on pigeons, Whitman wrote:
His [Darwin’s] triumph has won for us a common height from which we see the whole world of living beings as well as all inorganic nature; phenomena of every order we now regard as expressions of natural causes. The supernatural has no longer a standing in science; it has vanished like a dream, and the halls consecrated to its thraldom of the intellect are becoming radiant with a more cheerful faith.
In fact, Whitman’s orthogenesis arose from his mechanical perspective, not in opposition to his former life’s work. The orthogenetic trend did not follow a mystical impulse from outside, but a mechanistic drive from within, based upon admittedly unknown laws of genetics and embryology. His work on cell lineages had mapped the fate of earliest cells in the embryo, and had indicated that the source of eventual organs could be specified even in the tiny and formless clump of initial cells. If embryos grew so predictably, why should evolutionary change be devoid of similar order. “I venture to assert,” Whitman wrote, “that variation is sometimes orderly and at other times rather disorderly, and that the one is just as free from teleology as the other…. If a designer sets limits to variation in order to reach a definite end, the direction of events is teleological; but if organization and the laws of development exclude some lines of variation and favor others, there is certainly nothing supernatural in this.”
2. Whitman’s evidence. Modern detractors who misconstrue orthogenesis as old-fashioned teleology often assume that its supporters could only have been working on hope and the flimsiest of supposed evidence. But Whitman spent decades gathering reams of fascinating data (not all properly interpreted in our view, but still full of interest). He marshaled three major sources of evidence to support his orthogenetic theory: breeding, comparative anatomy, and ontogeny (the growth of individual birds).
In breeding, he found that he could develop a two-barred race from checkered parents by selecting birds with the weakest checkers in each generation. But he could never produce checkered birds from two-barred progenitors. In comparative anatomy, he argued that species judged more ancestral on other criteria grew plumages of early stages in the orthogenetic series. In ontogeny, he found that juvenile plumage exhibited earlier stages than adult feathers (a juvenile bird might moult its checkered feathers and then grow a two-barred adult plumage). Most nineteenth-century biologists believed that “ontogeny recapitulates phylogeny”—a mouthful meaning that individuals, in their embryology and growth, tend to pass through stages representing adult forms of their ancestry. Juvenile plumage would therefore represent an ancestral condition. The law of recapitulation is wrong (see my book, Ontogeny and Phylogeny), but you can’t blame Whitman for accepting the consensus of his time.
3. Channels versus one-way streets. Whitman conceived his series of orthogenetic stages as a forced pathway—a one-way street with pigeons as the cars. He was clearly wrong in this vision, and two major errors invalidate his form of orthogenesis. First, the cars can go in either direction; Whitman’s series may carve a road into a complex landscape, but the traffic flows both ways. Pigeons can either gain or lose color. Second, I doubt that either the checkered or two-barred condition represents a primitive state for domestic pigeons. The ancestor of domestic races was a population, not an individual—and populations are variable. I suspect that the parental population included both checkered and two-barred birds within a spectrum of variation—and that the spectrum represents the ancestral condition.
But think about Whitman’s vision in a slightly modified form, and we encounter an idea that is not only valid, but also full of potential insight for correcting a major misconception and teaching a fundamental truth about evolution. Think of his one-way street as a channel instead—a favored pathway of evolutionary variation set by the inherited genetic and developmental programs of organisms.
If natural selection controlled evolution entirely, then no such limits and pathways would
exist, and organisms would be like billiard balls, capable of movement in any direction and subject to any change in position induced by the pool cue of natural selection. But, to borrow an old metaphor from Francis Galton (see Essay 27 for a full explication), suppose that organisms are polyhedrons rather than billiard balls—and that they can only move by flipping from one side (on which they now rest) to an adjacent facet. They may need a push from natural selection to move at all, but internal limitations and possibilities set the direction of possible change. If inherited genetic and developmental programs build the facets of Galton’s polyhedron, then strong internal constraints upon evolutionary change must exist and Whitman’s insight is correct, so long as we convert his one-way streets into channels—that is, strong biases in the direction of variation available for evolutionary change. Moreover, Whitman probably identified the most important internal channel of all—the pathway of ontogeny, or the growth of individuals. Evolutionary change proceeds most readily in directions already established in growth—lengthening a bit here, cutting out a stage or two there, changing the relative timing of development among organs and parts.
The most serious of vernacular misconceptions views evolution as an inexorable machine, working to produce optimal adaptations as best solutions to problems posed by local environments and unconstrained by the whims and past histories of organisms. For example, I have monitored the “Ask the Boston Globe” science query column for years and have never seen anything but adaptationist answers to evolutionary questions. One correspondent asked, “Why do we have two breasts?” and the paper responded that the “right” number of nipples (for optimal adaptation) is one more than the usual complement of offspring, thus providing a margin of safety, but not so large a surplus to become a burden. Since human females almost always have but a single child, two become the right number of breasts by this argument rooted in natural selection. I couldn’t help but laugh when I read this conclusion. I do grasp the logic, but surely the primary channel of our anatomical design—bilateral symmetry—has some relevance to the solution. Most externalities come in twos on our bodies—eyes, nostrils, ears, arms, legs, etc.—and the reason cannot be singleton births. Isn’t this prior channel of architecture more likely to supply the primary reason for two breasts?
If the purely adaptationist vision were valid, we might gain the comfort of seeing ourselves, and all other creatures, as quintessentially “right,” at least for our local environments of natural selection. But evolution is the science of history and its influence. We come to our local environments with the baggage of eons; we are not machines newly constructed for our current realities. These historical baggages are expressed as the genetic and developmental channels that led Whitman too far. But these same channels, properly interpreted as strong biases in variation rather than one-way streets of change, would give us a much richer view of evolution as a subtle balance between constraints of history and reshapings by natural selection.
The power of these channels provides a key to understanding our bodies and our minds; we will never grasp the evolutionary contribution to our nature if we persist in the naive view that natural selection builds best solutions. We can accept the idea more readily for our bodies; hernias and lower back pain are the price we pay for walking upright with bodies evolved for quadrupedal life and not optimally redesigned. But how much of the quirkiness and limitations of our modes of thinking might also record a structure evolved during eons for other uses, and only recently adding the varied phenomena of higher consciousness and its primary tool of expression in language? Why are we so bad at so many mental operations? Why do we seem so singularly unable to grasp probability? Why do we classify by the painfully inadequate technique of dichotomy? Why can we not even conceive of infinity and eternity? Is the limit of current cosmological thinking a defect of data, or a property of mind that gives us no access to more fruitful kinds of answers?
I do not intend this list as a statement of despair about our mental midgetry. To recognize a potential limit is to think about tools of possible transcendence. Freedom, as Spinoza said, is the recognition of necessity. Let us return once again to the proper metaphor of channels and remember the finest statement in literature about emerging from ruts: “There is a tide in the affairs of men, which, taken at the flood, leads on to fortune.”
26 | The Great Seal Principle
TENNYSON’S In Memoriam, published in 1850, was surely the most popular of Victorian poems. The good queen herself remarked to her poet laureate, following the death of her beloved husband, Prince Albert: “Next to the Bible, In Memoriam is my comfort.” As a paradoxical and ultimate testimony of success, many lines became so popular, so much a part of everyday speech, that their relatively recent source was forgotten and a false Shakespearian or biblical origin often assumed. Be honest now; didn’t you think that Shakespeare wrote:
’Tis better to have loved and lost
Than never to have loved at all.
(In Memoriam also gave us, nearly a decade before Darwin’s book, the classic metaphor for natural selection: “nature red in tooth and claw.”)
After loving and losing, the most famous misattributed line from In Memoriam must be:
He seems so near, and yet so far.
Tennyson’s image provides an excellent epitome for that constant and unwelcome companion of intellectual life: frustration. I may be fascinated by big questions—the ultimate origin of the universe, for example—but I am not frustrated because I expect no near or immediate solution. Frustration lies just beyond the finger tip—the solution that is almost palpable, but for one little, stubborn obstacle.
Scientific frustration takes two primary forms. In the usual, empirical variety, deeply desired data lie just beyond our reach. Remember that we looked at the moon for millennia, but never knew the form of her back face (and couldn’t really develop a decent theory of origin and subsequent history without this information). So near (if we could only grab hold of the damned thing and turn it around)—and yet so far (a good quarter of a million miles). One space probe and a camera resolved this frustration of the ages.
A second species of frustration arises from logical problems, and these sometimes seem more intractable because solutions must come from inside our heads. Consider the classics, Zeno’s paradoxes, or the puzzles of our primers:
Brothers and sisters have I none
But that man’s father is my father’s son.
Again, the answers seem so close (after all, the arrow does move and Achilles does pass the tortoise), yet the structure of resolution eludes us.
Empirical frustrations are resolved by evidence; I don’t know that they present much of a general message beyond the obvious value of data over casuistry. Logical frustrations have more to teach us because solutions require a reorientation of mental habits (if only the minor realization that problems need not be viewed as external to their posers, and therefore “objective”: The man in the puzzling couplet is pointing to his own son).
The study of evolution is beset with frustration, most of the empirical variety (inadequacy of the fossil record, our inability to track and document enough members of a population). But the profession also features some persistent logical puzzles, most treated (and some resolved) by Darwin himself. Several take a similar form, roughly: “I can figure out why a particular feature is useful to an organism once it develops, but how could it arise in the first place?” I have treated one standard form of this puzzle in several essays—the “10 percent of a wing” problem, or how can wings evolve if tiny initial stages could confer no aerodynamic benefit? Darwin’s solution, now experimentally confirmed (see Essay 9 in Bully for Brontosaurus), argues that initial stages functioned in a different manner (perhaps for thermoregulation in the case of incipient wings), and were later coopted, when large enough, for their current use in flight.
A related and equally thorny problem asks why a useful evolutionary trend can begin in the first place and why one pathway is t
aken in a large potential field. The knee-jerk adaptationist answer—“because the evolved feature works so well (and must therefore, in some sense, have been prefavored as a solution)”—simply will not do, for current utility and historical origin are entirely separate issues. (What, in nature, works better than a wing?—and yet we all agree that benefit in flight did not initiate the trend).
Darwin also thought about this issue and proposed a solution. His argument features a trio of important properties: it is interesting, probably correct, and largely unappreciated. Darwin considered the classic case of mimicry in butterflies—the convergence of a tasty species on the pattern of a noxious form, all the better to fool predators (viceroy on monarch, for example). A potential mimic may share an environment with one hundred other butterfly species. Why converge upon one, rather than any of the ninety-nine others? And why initiate such a trend at all among so many other evolutionary possibilities? Darwin argued that the inception must reside in accident, whatever the predictable character of the trend once it starts, and whatever the resulting benefit. The mimic’s ancestor must begin with a slight and fortuitous resemblance to the species eventually copied. Such predispositions can only be chancy, for a species cannot know its complex future. A beginning “leg up” can nudge the trend into a particular path. The path itself will be carved by the deterministic force of natural selection, but the push into the path requires a bit of luck. Without an initiation in nonadaptive good fortune, the final and stunning adaptation could never evolve.
I am tempted to call this logical solution the “great seal principle,” to honor the motto of our national emblem (engraved on the flip side of a dollar bill)—annuit coeptis. The agent is usually construed as God and the line, following our gender-biased tradition, therefore translated as “he smiles on our beginnings.” But the Latin third-person singular is androgynous, and I prefer to think of the agent as Lady Luck—therefore, “she smiles on the initiations.”