I Have Landed

by Stephen Jay Gould

  As our fight for good (and politically untrammeled) public education in science must include the 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 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 defining language. But we should also note that Darwin himself never used the word “evolution” in his epochal book of 1859, the Origin of Species, where he calls this fundamental biological process “descent with modification.” Darwin, needless to say, did not shun “evolution” for motives of fear, conciliation, or political savvy—but rather for an opposite and principled reason that can help us to appreciate the depth of the intellectual revolution that he inspired, and some of the reasons (understandable if indefensible) for persisting public unease.

  Pre-Darwinian concepts of evolution—a widely discussed, if unorthodox, view of life in early-nineteenth-century biology—generally went by such names as “transformation,” “transmutation,” or “the development hypothesis.” In choosing a label for his very different account of genealogical change, Darwin would never have considered “evolution” as a descriptor because this vernacular English word implied a set of consequences contrary to the most distinctive features of his own revolutionary mechanism of change—the hypothesis of natural selection.

  “Evolution,” from the Latin evolvere, literally means “to unroll”—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 to seven-teenth-century English poetry, where the key meaning of sequential exposure of prepackaged potential inspired the first recorded usages in our language. For example, Henry More (1614–1687), the British poet and philosopher responsible for most seventeenth-century citations in the OED, 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 in 1832), Charles Lyell generally uses the neutral term “transmutation”—except in one passage, when he wishes to highlight a claim for progress: “The testacea [shelled invertebrates] 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 the Origin of Species, Darwin does use the verbal form “evolved”—clearly in the vernacular sense and in an especially prominent spot: as 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. Thus Darwin ends his great book:

  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 this word. For the mechanism of natural selection only yields increasing adaptation to changing local environments, not predictable “progress” in the usual sense of cosmic or general “betterment” expressed in favored Western themes of growing complexity or augmented mentality. 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 the most intricate creature, exquisitely adapted in all parts to a complex and dangerous external environment. Moreover, since natural selection can only adapt organisms 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—absence of inherent directionality and lack of predictability—the process regulated by natural selection could scarcely have suggested, to Darwin, the label of “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 great 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 only conceptualize genealogical transmutation 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 most 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 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 The Descent of Man, published in 1871. (Still, Darwin never cited “evolution” in the title of any book—and he chose, in labeling his major work on our species, to emphasize our genealogical “descent,” not our “ascent” to higher levels of consciousness.)

  When I was a young boy, growing up on the streets of New York City, the 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 eventua
lly 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 generally follow the strategy of selecting odd little tidbits as illustrations of general themes. I wrote this piece to celebrate the reopening of the Hayden Planetarium in 2000, and I followed my passion for apparent trivia with large tentacles of implication by marking this great occasion with a disquisition on something so arcane and seemingly irrelevant as the odyssey of the term “evolution” in my two old loves of biology and astronomy. In fact, I chose to write about “evolution” in the biological domain that I know in order to explicate a strikingly different meaning of “evolution” in the profession that I put aside, but still love avocationally. I believe that such a discussion of the contrast between biological and cosmological “evolution” might highlight an important general point about alternative worldviews, and also serve 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 better won by principled separation and mutual respect, based on clear definitions and distinctions among truly disparate processes, 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 of a species and the life of a star—partly, at least, for the very bad reason that both professions use the term “evolution” to designate change through time. In this case, the fundamental differences embody far more interest and insight than the superficial similarities—and true unity will only be achieved 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 a twofold process of generating copious and undirected variation within a population, and then passing 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 (such as average size or average braininess) among successive populations through time. For this fundamental reason, we call such theories of change “variational” as opposed to more conventional, and more direct, models of “transformational” change imposed by natural laws that mandate a particular trajectory based on inherent, and therefore predicable, 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 temporal sequence and 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, in the flower of youthful strength but before any reproductive action, fall into a crevasse and die.) Because offspring inherit their parental degree of hairiness, the next generation will include 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 to 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 flow from the variational basis of natural selection—including the sensible and explainable, but quite unpredictable, nature of the outcome (dependent upon complex and contingent changes in local environments), and the nonprogressive character of the alteration (adaptive only to these unpredictable local circumstances and not building a “better” elephant in any cosmic or general sense).

  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 push me there directly, than if I must rely upon 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—leading to the reconceptualization of Homo sapiens as an unpredictable and not necessarily 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, or even actively to resist, its truly liberating content. (I must leave the issue of liberation for another time, but once we recognize that the specification of morals and the search for a meaning in our lives cannot be resolved by scientific data in any case, then Darwin’s variational mechanism will no longer seem threatening, and may even become liberating as a rationale for abandoning a chimerical search for the purpose of our lives, and 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 invoke a variational theory like Darwin’s. 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 vernacular definition of “evolution”—even though the term now holds far wider scientific currency in 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 historical cosmic changes that do exhibit the key features of biological “evolution”—unpredictability and lack of inherent directionality.

  As an illustration of this astronomical usage, consider the most standard and conventional of all sources—the Encyclopaedia Britannica article (fifteenth edition, 1990) on “stars and star clusters.” The section on “star formation and evolution” begins by analogizing stellar “evolution” to a preprogrammed life cycle, with degree of “evolution” defined as position along the predictable trajectory:

  Throughout the Milky Way Galaxy . . . astronomers have discovered stars that are well evolved or even approaching extinction, or both, as well as occasional stars that must be very young or still in the process of formation. Evolutionary effects on these stars are not negligible.

  The fully predictable and linear sequence of stages in a stellar “lifetime” (“evolution” to astronomers) records the consequences of a defining physical process in the construction and history of stars: the conversion of mass to energy, with a depletion of hydrogen and transformation to helium:

  The spread of luminosities and colors of stars within the main sequence can be understood as a consequence of evolution. . . . As the stars evolve, they adjust to the increase in the helium-to-hydrogen ratio in their cores. . . . When the core fuel is exhausted, the internal structure of the star changes rapidly; it quickly leaves the main sequence and moves towards the region of giants and supergiants.