Natural History
Feb, 2000
What does the dreaded "E" word mean, anyway.
Author/s: Stephen Jay Gould
A reverie for the opening of the new Hayden Planetarium.
Evolution posed no terrors in the liberal constituency of New York City when I studied biology at Jamaica High School in 1956. But our textbooks didn't utter the word either--a legacy of the statutes that had brought William Jennings Bryan and Clarence Darrow to legal blows at Tennessee's trial of John Scopes in 1925. The subject remained doubly hidden within my textbook--covered only in chapter 63 (of 66) and described in euphemism as "the hypothesis of racial development."
The antievolution laws of the Scopes era, passed during the early 1920s in several southern and border states, remained on the books until 1968, when the Supreme Court declared them unconstitutional. The laws were never strictly enforced, but their existence cast a pall over American education, as textbook publishers capitulated to produce "least common denominator" versions acceptable in all states--so schoolkids in New York got short shrift because the statutes of some distant states had labeled evolution dangerous and unteachable.
Ironically, at the very end of this millennium (I am writing this essay in late November 1999), demotions, warnings, and anathemas have again come into vogue in several regions of our nation. The Kansas school board has reduced evolution, the central and unifying concept of the life sciences, to an optional subject within the state's biology curriculum--an educational ruling akin to stating that English will still be taught but that grammar may henceforth be regarded as a peripheral frill, permitted but not mandated as a classroom subject. Two states now require that warning labels be pasted (literally) into all biology textbooks, alerting students that they might wish to consider alternatives to evolution (although no other well-documented scientific concept evokes similar caution). Finally, at least two states have retained all their Darwinian material in official pamphlets and curricula but have replaced the dreaded "e" word with a circumlocution, thus reviving the old strategy of my high school text.
As our fight for good (and politically untrammeled) public education in science must include our forceful defense of a key word--for inquisitors have always understood that an idea can be extinguished most effectively by suppressing all memory of a defining word or an inspirational person--we might consider an interesting historical irony that, properly elucidated, might even aid us in our battle. We must not compromise our showcasing of the "e" word, for we give up the game before we start if we grant our opponents control over basic terms. But we should also note that Darwin himself never used the word "evolution" in his epochal book of 1859. In Origin of Species, he calls this fundamental biological process "descent with modification." Darwin, needless to say, did not shun "evolution" from motives of fear, conciliation, or political savvy but rather for an opposite and principled reason that can help us appreciate the depth of the intellectual revolution that he inspired and some of the reasons (understandable if indefensible) for the persistent public unease.
Pre-Darwinian terminology for evolution--a widely discussed, if unorthodox, view of life in early nineteenth-century biology--generally used such names as transformation, transmutation, or the development hypothesis. In choosing a label for his own, very different account of genealogical change, Darwin would never have considered "evolution" as a descriptor, because that vernacular English word implied a set of consequences contrary to the most distinctive features of his proposed revolutionary mechanism of change.
"Evolution," from the Latin evolvere, literally means "an unrolling"--and clearly implies an unfolding in time of a predictable or prepackaged sequence in an inherently progressive, or at least directional, manner (the "fiddlehead" of a fern unrolls and expands to bring forth the adult plant--a true evolution of preformed parts). The Oxford English Dictionary traces the word "evolution" to seventeenth-century English poetry. Here the word's key meaning--the sequential exposure of prepackaged potential--inspired the first recorded usages in our language. For example, Henry More (1614-87), the British philosopher responsible for several of the seventeenth-century citations in the OED entry, stated in 1664,"I have not yet evolved all the intangling superstitions that may be wrapt up."
The few pre-Darwinian English citations of genealogical change as "evolution" all employ the word as a synonym for predictable progress. For example, in describing Lamarck's theory for British readers (in the second volume of his Principles of Geology, 1832), Charles Lyell generally uses the neutral term "transmutation"--except in one passage, where he wishes to highlight a claim for progress: "The testacea of the ocean existed first, until some of them by gradual evolution were improved into those inhabiting the land."
Although the word "evolution" does not appear in the first edition of Origin of Species, Darwin does use the verbal form "evolved" clearly in the vernacular sense and in an especially crucial spot: the very last word of the book! Most students have failed to appreciate the incisive and intended "gotcha" of these closing lines, which have generally been read as a poetic reverie, a harmless linguistic flourish essentially devoid of content, however rich in imagery. In fact, the canny Darwin used this maximally effective location to make a telling point about the absolute glory and comparative importance of natural history as a calling.
We usually regard planetary physics as the paragon of rigorous science, while dismissing natural history as a lightweight exercise in dull, descriptive cataloging that any person with sufficient patience might accomplish. But Darwin, in his closing passage, identified the primary phenomenon of planetary physics as a dull and simple cycling to nowhere, in sharp contrast with life's history, depicted as a dynamic and upwardly growing tree. The Earth revolves in uninteresting sameness, but life evolves by unfolding its potential for ever expanding diversity along admittedly unpredictable, but wonderfully various, branchings:
Whilst this planet has gone cycling on according to the fixed law of
gravity, from so simple a beginning endless forms most beautiful and most
wonderful have been, and are being, evolved.
But Darwin could not have described the process regulated by his mechanism of natural selection as "evolution" in the vernacular meaning then conveyed by the word. For the mechanism of natural selection yields only increasing adaptation to changing local environments, not predictable progress in the usual sense of cosmic or general betterment expressed as growing complexity, augmented mentality, or whatever. In Darwin's causal world, an anatomically degenerate parasite, reduced to a formless clump of feeding and reproductive cells within the body of a host, may be just as well adapted to its surroundings, and just as well endowed with prospects for evolutionary persistence, as is the most intricate creature, exquisitely adapted in all parts to a complex and dangerous external environment. Moreover, since natural selection can adapt organisms only to local circumstances, and since local circumstances change in an effectively random manner through geological time, the pathways of adaptive evolution cannot be predicted.
Thus, on these two fundamental grounds--lack of inherent directionality and lack of predictability--the process regulated by natural selection could scarcely have suggested, to Darwin, the label "evolution," an ordinary English word for sequences of predictable and directional unfolding. We must then, and obviously, ask how "evolution" achieved its coup in becoming the name for Darwin's process--a takeover so complete that the word has now almost (but not quite, as we shall soon see) lost its original English meaning of "unfolding" and has transmuted (or should we say "evolved"?) into an effective synonym for biological change through time.
This interesting shift, despite Darwin's own reticence, occurred primarily because a grea
t majority of his contemporaries, while granting the overwhelming evidence for evolution's factuality, could not accept Darwin's radical views about the causes and patterns of biological change. Most important, they could not bear to surrender the comforting and traditional view that human consciousness must represent a predictable (if not a divinely intended) summit of biological existence. If scientific discoveries enjoined an evolutionary reading of human superiority, then one must bow to the evidence. But Darwin's contemporaries (and many people today as well) would not surrender their traditional view of human domination, and therefore could conceptualize genealogical transmutation only as a process defined by predictable progress toward a human acme--in short, as a process well described by the term "evolution" in its vernacular meaning of "unfolding an inherent potential."
Herbert Spencer's progressivist view of natural change probably exerted the greatest influence in establishing "evolution" as the general name for Darwin's process, for Spencer held a dominating status as Victorian pundit and grand panjandrum of nearly everything conceptual. In any case, Darwin had too many other fish to fry and didn't choose to fight a battle about words rather than things. He felt confident that his views would eventually prevail, even over the contrary etymology of a word imposed upon his process by popular will. (He knew, after all, that meanings of words can transmute within new climates of immediate utility, just as species transform under new local environments of life and ecology!) Darwin never used the "e" word extensively in his writings, but he did capitulate to a developing consensus by referring to his process as evolution for the first time in Descent of Man, published in 1871. (Still, Darwin never used the word "evolution" in the title of any book--and he chose, in his book on human history, to emphasize the genealogical "descent" of our species, not our "ascent" to higher levels of consciousness.)
When I was a young boy, growing up on the streets of New York City, the American Museum of Natural History became my second home and inspiration. I loved two exhibits most of all--the Tyrannosaurus skeleton on the fourth floor and the star show at the adjacent Hayden Planetarium. I juggled these two passions for many years and eventually became a paleontologist; Carl Sagan, my near-contemporary from the neighboring neverland of Brooklyn (I grew up in Queens) weighed the same two interests in the same building but opted for astronomy as a calling. (I have always suspected a basic biological determinism behind our opposite choices. Carl was tall and looked up toward the heavens; I am shorter than average and tend to look down at the ground.)
My essays may be known for their tactic of selecting odd little tidbits as illustrations of general themes. But why, to mark the reopening of the Hayden Planetarium, would I highlight such a quirky and apparently irrelevant subject as the odyssey of the term "evolution" in scientific, and primarily biological, use---thus seeming, once again, to reject the cosmos in favor of the dinosaurs? Method does inhere in my apparent madness (whether or not I succeed in conveying this reasoning to my readers). I am writing about the term "evolution" in the domain I know in order to explicate its strikingly different meaning in the profession that I put aside but still love avocationally. A discussion of the contrasts between biological evolution and cosmological evolution might offer some utility as a commentary about alternative worldviews and as a reminder that many supposed debates in science arise from confusion engendered by differing uses of words and not from deep conceptual muddles about the nature of things.
Interdisciplinary unification represents a grand and worthy goal of intellectual life, but greater understanding can often be won by principled separation and mutual respect, based on clear definitions and distinctions among truly disparate processes, rather than by false unions forged with superficial similarities and papered over by a common terminology In our understandable desire to unify the sciences of temporal change, we have too often followed the Procrustean strategy of enforcing a common set of causes and explanations upon the history or a species and the life or a star--partly, at least, for the very bad reason that both professions use the term "evolution" to denote change through time. In this case, the fundamental differences trump the superficial similarities-and true unity will be achieved only when we acknowledge the disparate substrates that, taken together, probe the range of possibilities for theories of historical order.
The Darwinian principle of natural selection yields temporal change--evolution in the biological definition--by the twofold process of producing copious and undirected variation within a population and then passing along only a biased (selected) portion of this variation to the next generation. In this manner, the variation within a population at any moment can be converted into differences in mean values (average size, average braininess) among successive populations through time. For this fundamental reason, we call such theories of change variational as opposed to the more conventional, and more direct, models of transformational change imposed by natural laws that mandate a particular trajectory based on inherent (and therefore predictable) properties of substances and environments. (A ball rolling down an inclined plane does not reach the bottom because selection has favored the differential propagation of moving versus stable elements of its totality but because gravity dictates this result when round balls roll down smooth planes.)
To illustrate the peculiar properties of variational theories like Darwin's in an obviously caricatured, but not inaccurate, description: Suppose that a population of elephants inhabits Siberia during a warm interval before the advance of an ice sheet. The elephants vary, at random and in all directions, in their amount of body hair. As the ice advances and local conditions become colder, elephants with more hair will tend to cope better, by the sheer good fortune of their superior adaptation to changing climates--and they will leave more surviving offspring on average. (This differential reproductive success must be conceived as broadly statistical and not guaranteed in every case: in any generation, the hairiest elephant of all may fall into a crevasse and die.) Because offspring inherit their parents' degree of hairiness, the next generation will contain a higher proportion of more densely clad elephants (who will continue to be favored by natural selection as the climate becomes still colder). This process of increasing average hairiness may continue for many generations, leading to the evolution of woolly mammoths.
This little fable can help us understand how peculiar and how contrary to all traditions of Western thought and explanation the Darwinian theory of evolution, and variational theories of historical change in general, must sound to the common ear. All the odd and fascinating properties of Darwinian evolution--the sensible and explainable but quite unpredictable nature of the outcome (dependent upon complex and contingent changes in local environments), the nonprogressive character of the alteration (adaptive only to these unpredictable local circumstances and not inevitably building a "better" elephant in any cosmic or general sense)--flow from the variational basis of natural selection.
Transformational theories work in a much simpler and more direct manner. If I want to go from A to B, I will have so much less conceptual (and actual) trouble if I can postulate a mechanism that will just push me there directly than if I must rely upon the selection of "a few good men" from a random cloud of variation about point A, then constitute a new generation around an average point one step closer to B, then generate a new cloud of random variation about this new point, then select "a few good men" once again from this new array--and then repeat this process over and over until I finally reach B.
When one adds the oddity of variational theories in general to our strong cultural and psychological resistance against their application to our own evolutionary origin (as an unpredictable and not necessary progressive little twig on life's luxuriant tree), then we can better understand why Darwin's revolution surpassed all other scientific discoveries in reformatory power and why so many people still fail to understand, and may even actively resist, its truly liberating content. (I must leave the issue of liberation for another time, but once we recogni
ze that the specification of morals and the search for a meaning to our lives cannot be accomplished by scientific study in any case, then Darwin's variational mechanism will no longer seem threatening and may even become liberating in teaching us to look within ourselves for answers to these questions and to abandon a chimerical search for the purpose of our lives, and for the source of our ethical values, in the external workings of nature.)
These difficulties in grasping Darwin's great insight became exacerbated when our Victorian forebears made their unfortunate choice of a defining word--"evolution"--with its vernacular meaning of "directed unfolding." We would not face this additional problem today if "evolution" had undergone a complete transformation to become a strict and exclusive definition of biological change--with earlier and etymologically more appropriate usages then abandoned and forgotten. But important words rarely undergo such a clean switch of meaning, and "evolution" still maintains its original definition of "predictable unfolding" in several nonbiological disciplines-including astronomy.
When astronomers talk about the evolution of a star, they clearly do not have a variational theory like Darwin's in mind. Stars do not change through time because mama and papa stars generate broods of varying daughter stars, followed by the differential survival of daughters best adapted to their particular region of the cosmos. Rather, theories of stellar "evolution" could not be more relentlessly transformational in positing a definite and predictable sequence of changes unfolding as simple consequences of physical laws. (No biological process operates in exactly the same manner, but the life cycle of an organism certainly works better than the evolution of a species as a source of analogy.)
Ironically, astronomy undeniably trumps biology in faithfulness to the etymology and the vernacular definition of "evolution"--even though the term now holds far wider currency under the radically altered definition of the biological sciences. In fact, astronomers have been so true to the original definition that they confine "evolution" to historical sequences of predictable unfolding and resolutely shun the word when describing cosmic changes exhibiting the key features of biological evolution--unpredictability and lack of inherent directionality.
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