The Accidental Species: Misunderstandings of Human Evolution

by Henry Gee

  But how much time is “enough”? Darwin envisaged that change would be slow, perhaps even imperceptible on the scale of human lifetimes, and reasoned that many millions of years would be required for natural selection to transform a blob of primordial protoplasm into the diversity of animals and plants we see all around us. The problem was that, in Darwin’s youth, such time didn’t exist. So no matter how obvious heritable variation, superabundance, and environmental change are to every child and countryman, without time, natural selection wouldn’t be able to do very much.

  What do I mean by time “not existing”? I’m being deliberately arch here. Nowadays we are accustomed to thinking of the earth as very old—around 4,500,000,000 years old, in fact—plenty of time for natural selection to have done its work. We are inclined to take such things for granted, so it’s very hard for us to put ourselves into the minds of the average Victorian who had no reason to doubt that the earth was any more than the 5,500 years or so required by the Bible. It took quite a long time for even those interested in the subject to realize that the earth is very much older than this, and even then, only when they were confronted by an otherwise insupportable weight of evidence. (The many people who to this day cling to the old biblical timescale have no such excuse.)

  And that’s it. Take heritable variation, the changeable environment, superabundance, and time. All these things can be seen—or, at least, understood—by anyone.

  So much for natural selection. What, then, about evolution? How is one related to the other? The terms are not equivalent, and that’s part of the problem. Here I hope to disentangle the word from some of its ancient baggage, look into its history as a word as well as a concept, and show what (I think) Darwin meant it to mean—which is (I think) rather different from what most people think when they use the term. In fact, I’d go as far as saying that it would be hard to find a worse choice of word than “evolution” to describe what Darwin, very sensibly, called “descent with modification.” To Darwin, the word “evolution” did not mean what we think it means today.

  As you might expect, the word has Latin roots. According to the online Oxford English Dictionary, henceforth OED,7 the Roman writer Cicero used evolutio to mean the action of unrolling a scroll. Thus was born the concept of evolution as a process of development, elaboration, and, with it, revelation—that is, the deliberate transformation, by the action of unrolling, of a closed scroll to an open one whose information might be read: an orderly dance from simplicity into complexity. Medieval Latin texts use the term to refer to the passage of time during which any metaphorical unrolling might take place.

  The first recorded use of the word “evolution” in English was in 1616, in a translation of the Tactics by the second-century Greek military historian Aelian (Aelianus Tacticus), where it means, quite specifically, the movement of forces from one position to another:

  The nature of this Euolution is clearely to leaue the File-leaders in front, and Bringers-vp in reare.

  This nuanced view of evolution, as a series of maneuvers along a studied course from known beginning to desired conclusion, broadened to describe the occult movements of the wands of wizards, the gyrations of gymnasts, and, eventually, the choreography of dancers. The many examples given by the OED have one thing in common—that the term “evolution” in this sense came to encapsulate an exact, directed and predetermined series of events, as predetermined as a choreographed dance routine. More generally, the word “evolution” came to mean the opening out or unfolding of a series of events in an orderly succession, or the action of elaborating a simple idea into something more rounded, very much by analogy with Cicero’s unfurling scroll. As an aside, almost, consider this notable example from Erasmus Darwin’s Zoonomia (1801):

  The world . . . might have been gradually produced from very small beginnings . . . rather than by a sudden evolution of the whole by the Almighty fiat.

  Given what we think we know of evolution—as a gradual process—it is startling to come across Charles Darwin’s grandfather Erasmus using the term in precisely the opposite sense.

  Those admen I lampooned in chapter 1 would find in the OED plenty of precedents for their use of the term “evolution” to refer to the refinement of consumer products (the first recorded such usage being in 1882). But in biology, as in life more generally, the term began to be used very much by way of analogy with Cicero’s original meaning—the elaboration of something simple into something more complex, such as a plant from a germinating seed, or the development of a butterfly from a caterpillar—like so many scrolls unrolling, each in its own precise, preprogrammed manner. Here is an entry from the earliest days of the Philosophical Transactions of the Royal Society, in 1670:

  By the word Change is nothing else to be understood but a gradual and natural Evolution and Growth of the parts.

  And once again from Erasmus Darwin:

  The gradual evolution of the young animal or plant from its egg or seed.

  As a term, evolution gets around. I haven’t mentioned the several different usages of “evolution” in mathematics, astronomy, and chemistry. All of the above, of course, is by way of a curtain-raiser to what the OED lists as sense 8 of evolution (out of eleven), namely “the transformation of animals, plants and other living organisms into different forms by the accumulation of changes over successive generations.” The first recorded use of “evolution” in this sense is in 1832, in Charles Lyell’s Principles of Geology, a work with which Charles Darwin was very familiar.

  The testacea of the ocean existed first, until some of them by gradual evolution, were improved into those inhabiting the land.

  As I noted, Darwin did not use the word “evolution” in the Origin (and continued not to do so until the sixth edition of 1873). He did, however, use the word “evolved.” It appears once, as the very last word in the book, the final word of a justifiably famous paragraph.

  There is grandeur in this view of life, with its several powers, having been originally breathed by the Creator into a few forms or into one; and that, 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.

  It is important to remember that Darwin was no Darwinist. He could hardly have used the words “evolution” or “evolved” in the sense we generally understand them today, given that it was his own work that was largely responsible for altering the balance of their usage—from Cicero’s unrolling scroll, to the transformation of organisms over geological time. We, however, are in a different position. To us, the shade of Darwin looms large. His insights have colored the way we think of ourselves and our place in nature.

  So, when Darwin used the word “evolved,” it was in the earlier sense, of something unfolding. Creatures would appear, perhaps in successively more elaborate forms, from simple beginnings—perhaps as an analogy with the production of a shoot from a seed, or a frog tadpole from a mass of spawn. Darwin was a great believer in the power of analogy. After all, his entire argument about natural selection was based on just such a comparison with the “artificial” selection that stockbreeders use to enhance the desirable traits in their charges.

  Darwin, therefore, used the word “evolved” to mean growth and development of a complex form from a simpler one, and used it to draw an analogy with the altogether grander process in which life itself would from simple beginnings become more diverse, elaborate, and complex. Darwin had a term for this process to which evolution was a mere analogy: he called it “descent with modification,” a much less loaded term than “evolution.”

  In general, though, when scientists in Darwin’s time and earlier referred to the gradual change of species—what we today call “evolution”—they used the word “transformation.” If evolution meant the unfolding of individual organisms, from seed to shoot, from egg to adult, then transformation meant the change in form of entire species, usually (though not necessarily) from simpler
forms to more complex ones.

  The two processes—evolution and transformation—were analogous, but distinct. Today, though, they have become conflated. When most people today talk of “evolution,” what they mean is “transformation.” This conflation has had the consequence of conferring a sense of direction and choreography onto the idea of Darwinian evolution. This is why people, when they think of “evolution,” imagine (for example) a series of individuals, each one an improvement on the one before, and if there are gaps in the series, they are “missing links”—pieces in a metaphorical chain whose beginning, end, and intermediate progress are already known.

  There are deeper roots to this conflation, however, but before I get to that, I must tempt you into a little digression about the nature of and evidence for Darwin’s descent with modification.

  Earlier I mentioned that the “community of descent” provides much evidence for descent with modification. By this I mean that all forms of life are organized in fundamentally the same way, down to the minutest detail, supporting the view that all life shares a common heritage. It’s worth considering this in a little more detail. As far as we know, all organisms owe their structure to the peculiar chemistry of the element carbon. Carbon atoms readily bind with one another and with atoms of other elements (notably oxygen, hydrogen, nitrogen, phosphorus, and sulfur) to produce highly elaborate molecules, sometimes disposed in long chains of smaller, similar units strung together. So it is that all organisms so far discovered carry genetic information in the form of long, carbon-based, chain-like molecules called nucleic acids, either DNA (deoxyribose nucleic acid) or the related form RNA (ribose nucleic acid). This information specifies the structure of a different set of chain-like, carbon-based molecules called proteins, and does so using a code that’s the same (albeit with minor variations), irrespective of the organism concerned. All organisms more complicated than viruses have cells, bounded by a membrane constructed of two layers of carbon-based, chain-like molecules called lipids, sometimes bound in an extracellular matrix made of chain-like carbon-based molecules such as cellulose or collagen. The contents of the cells are pretty much the same, irrespective of the organism in which they occur.

  The similarities between creatures at this most detailed level are so great that it’s a wonder that organisms as a whole come to look so different—from the worms burrowing beneath Darwin’s tangled bank to the birds and insects flitting above it. This underlying sameness is such compelling evidence for descent with modification that it would, according to Richard Dawkins (in his book The Greatest Show on Earth), stand alone, even had no fossils ever been discovered.

  Why is the evidence so strong? Because life needn’t have been arranged like that. It is possible to imagine systems that have some of the properties of life that use only some of the above features, or none. It is also possible to imagine a situation in which different living organisms sharing the same planet have fundamentally different constitutions. The fact that all life, no matter how various in form, is specified so minutely according to the same recipe suggests that all living creatures descend, ultimately, from a creature that had all these same fundamental features of inheritance and construction.

  So much for descent: what of modification? Darwin supposed that the pattern of inheritance might vary, the offspring of parents becoming sorted by natural selection, so that the offspring would come to look different from their parents. These differences would accumulate, and the offspring would spread and diversify. As with offspring and parents, so, eventually, with new species arising from existing ones. It is a testament to Darwin’s perspicacity that even though Darwin had no clue about the mechanisms of genetic variation, his suppositions have been borne out, innumerable times, and in exquisite detail.

  Darwin imagined that life, governed by such a process, would be connected in a treelike pattern, rather like a family tree, with one ancestor at the bottom—the root and trunk—and progressively more (and more diverse) descendants as the branches and twigs. Darwin’s conception of the treelike pattern of evolution formed the only illustration in the Origin. Darwin’s innovation was his invocation of a process, natural selection, acting in the here and now, which, when summed over history, produced this pattern.

  In geometrical terms, a tree is a box of boxes, a set of sets: one trunk gives off a number of branches, each of which gives off a bunch of twigs, each of which bears several leaves, and so on. The idea that life can be catalogued as a system of nested sets goes back to Aristotle, but it was formalized in the eighteenth century by the Swedish botanist Linnaeus, who originally devised the hierarchical means of classification we use today, in which species (erectus, sapiens) are grouped into more inclusive genera (Homo), which in turn are grouped with other genera into orders (Primates) and with other orders into classes (Mammalia). Linnaeus’s conception of life was profoundly and inevitably pre-evolutionary: he was organizing life simply as he (and everyone else) saw it.

  Scholars before Darwin thus had two distinct phenomena to explain. First was evolution—sometimes called generation—in which a small and simple germ was elaborated (“evolved”) into a large and complex adult. The second was the apparent arrangement of life in a hierarchical or treelike fashion.

  The analogy Darwin drew between evolution and transformation was not his own invention. Editions of William Harvey’s Exercitationes de generatione animalium (1651), one of the earliest works in the modern era to address the question of generation, bore engravings illustrating Zeus holding an egg from which all manner of creatures poured forth, with the legend “Ex Ovo, Omnia”—everything comes from the egg—a slogan that could be applied to generation and transformation with equal facility.

  A more explicit connection between the two processes was drawn by the adherents of “nature philosophy,” a tendency popular in the late eighteenth and early nineteenth centuries, and particularly associated with the poet, protoscientist, playwright, and all-around egghead Johann Wolfgang von Goethe. The nature philosophers were inclined to be somewhat romantic, which doesn’t always go down well among scientists, and it’s easy to make fun of them nowadays. However, they made two vital contributions to biological thought—one somewhat mystical, as one might expect; the other highly practical.

  Although people saw life arranged as a tree, they also noticed that trees grow upward, from the ground; that you need a ladder to climb a tree if it is tall; and that it takes more effort getting to the upper branches than sitting on the ground. The treelike arrangement was therefore in accord with the ancient idea of the “great chain of being,” in which living creatures occupied a station in life according to their structure, the simpler ones (worms, insects, and so on) toward the bottom, the more complex ones (fishes, birds, mammals) toward the top. Human beings would—noblesse oblige—occupy the topmost rung, above the apes, but below the angels.

  At first, this arrangement was simply a statement of the order of creation. There was no sense in which creatures on a lower rung could be transformed into creatures on a higher one. Some thinkers, however, began to question why the tree should be ordered in the way it was, rather than in any other way, and began to imagine processes whereby creatures might be transformed.

  Perhaps the most famous exponent of transformation before Darwin was Jean Baptiste de Lamarck, who outlined a scheme in his book Philosophie zoologique (1809) in which creatures would be driven to transform by an inner force or besoin (need) in response to their environmental circumstances, and such transformations would be inherited by any offspring. Thus the canonical picture of giraffes extending their necks ever longer to reach the highest leaves, and passing the results of their exertions onto baby giraffes, which would tend to have longer necks than their parents. This idea sounds quaint today, but Lamarckism was a theory with legs.

  Today we are inclined to think that after the publication of the Origin, Darwin’s ideas just went from strength to strength (such is our view of history as forever progressive), but this is no
t the case. Natural selection required that creatures provide a constant source of variation on which this selection could act. In Darwin’s time, though, no such mechanism was known. The discovery of genetics around the turn of the twentieth century was to answer the question and so rehabilitate Darwin, but for half a century—between Darwin’s death in 1882 and the reconciliation of evolution and genetics in the late 1930s—evolution by natural selection was in eclipse: influential scientists turned away from Darwinism for want of an explanation of variation, leaving evolution as not much more than a set of just-so stories. William Bateson—the scientist who would later coin the term “genetics”—was typically scathing.8 “In these discussions [of evolution] we are continually stopped by such phrases as ‘if such and such a variation then took place and was favourable,’ or, ‘we may easily suppose circumstances in which such and such a variation if it occurred might be beneficial,’ and the like . . . ‘If,’ say we with much circumlocution, ‘the course of Nature followed the lines we have suggested, then, in short, it did.’” As a result of this Darwinian vacuum, many mainstream thinkers continued to favor Lamarckism, so much so that it formed the grounding of university-level textbooks such as E. S. Russell’s classic Form and Function (1916).

  The nature philosophers looked at the pattern of life, but rather than Lamarckian besoin, a mechanism that was actually meant to cause transformation in the real world, they saw in each successively more elaborate form a more concrete manifestation of some ideal, cosmic striving toward perfection that would reach its acme in Man (with a capital M). Creatures in the real world were imperfect expressions of a transcendental ideal. No actual transformation was meant to have happened.