The Accidental Species: Misunderstandings of Human Evolution (7 page)

Darwin saw natural selection not as an agency in itself, but the ongoing result of the interaction of several factors. Creatures tend to produce offspring that vary, and this variation is heritable. They also tend to produce more of them than can possibly survive. Nature will select those few offspring that are most suited to living in the prevailing environment, in much the same way that a stockman will select those animals most suited to his ends. Given enough time, the creatures will change, their adaptations tracking changes in the environment.

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 ob
vious 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.