to nest on the ground. If rats, pigs, or humans should then arrive, these animals find themselves highly vulnerable to predation, or even extinction.
Darwin also realized that although behaviors and mental capacities seem somehow different from traits such as the color of a feather or the scent of a flower, they are not. This means that behaviors can evolve in the same way as any other trait. So if individuals vary in a behavior, and if that variation has some genetic basis, then the behavior can evolve through natural selection.
Over time, then, simple behaviors can potentially evolve into far more elaborate forms. To show how this could happen, Darwin takes the hexagonal combs built by honeybees and asks how the impulse to build such complex structures could have evolved through the slow accumulation of small but useful variations. This passage is one of the finest in the book; he sets up the full difficulty of the problem to be solved and then solves it with great elegance. The problem? Honeybees have evolved to build a complex comb that holds the maximum amount of honey while using the least amount of wax. To solve it, Darwin marshals evidence from other bees that build less complex combs, he writes to a mathematician to investigate the geometry of honeycombs, and he performs experiments to elucidate how honeybees actually build their combs. He concludes that the steps to making complex combs can be reduced to a few simple rules of thumb – and that the ability to follow these rules of thumb can readily evolve if the pressure to economize the use of wax is strong. If, that is, colonies that build more efficient combs tend to perpetuate themselves better than colonies whose combs are less efficient.
But the full magnificence of the Origin is this: it presents a worldview of extraordinary power, one that can explain the entire diversity of life on earth. The spiders, wombats, and algae; the earthworms, stag beetles, and luminous fungi; the tigers, oak trees, and all the rest; all the millions of different beings that are here on earth today as well as the countless billions that have lived here before are all bound together into a single tree of life, sculpted by forces of nature that we can identify and understand.
This worldview has several elements: through the tree of life, it gives kinship to all life forms; it predicts that every bacterium, beetle, or breadfruit tree can trace its ancestry back to the origin of life. In principle, then, it’s possible to draw a giant family tree, one that includes every being on the planet. But why are there so many different kinds of beings? This is due to what Darwin called “descent with modification,” meaning that over time, different populations evolve in different directions. This is, in part, because different populations experience natural selection in different ways: climates can be subtly different, local predators may be different, ditto the food, and so on. It is also, in part, because of what Darwin called “sexual selection,” which is the idea that by choosing who to mate with, males and females exert selection upon one another’s appearances, songs, scents, and other characteristics. Like natural selection, sexual selection can cause different populations to evolve in different directions. What’s more, sexual selection can interact with natural selection. A particularly good example of this interaction comes from recent research on guppies, small fish that live in streams. Female guppies prefer to mate with colorful males. Unfortunately, however, predators often find those males easier to see, so brighter males tend to get killed at a higher rate. Thus, in streams with large numbers of predators, males tend to evolve to be less flamboyant, whereas fewer predators leads to the evolution of more colorful males. Over time – especially immensely long periods of time, such as tens of millions of years – these various processes can produce spectacularly different outcomes in different places.
But there is something else to bear in mind. The substrate for all evolutionary change is genetic variation, which is ultimately caused by mutations to the information contained in DNA. If there is no variation for a trait, then that trait cannot evolve, even if evolution would be advantageous. For example, in one recent experiment, E. coli bacteria were grown in an environment that had a limited supply of glucose – the sugar they usually consume – but an abundance of citrate, which they usually cannot consume. It took more than thirty-one thousand generations for a citrate-consuming variant to appear. The reason is that evolving to consume citrate was not a matter of a single mutation, but of several. Still, even for bacteria that go through several generations every day, thirty-one thousand generations is a long time to wait. It also shows that evolution includes a sizeable dollop of chance – in this case, the chance that the necessary genetic variation will appear.
The tree of life, genetic variation, natural selection, sexual selection, chance, and time; these elements are all present in the Origin, and the view of evolution it presents is complete in outline. Yet the Origin is just that: the beginning of a new way of looking at life on earth, the first word on the subject, not the last. In the decades since 1859, Darwin’s ideas have been greatly developed and refined. Darwin himself led the charge; he published five further editions of the Origin in his lifetime, often revising heavily from one to the next. Some of the changes are corrections; others, responses to critics; still others incorporate new discoveries. By the sixth edition, which appeared in 1872, the text had grown to include a sketch of evolutionary thinking before the Origin, a glossary of terms, and an extra chapter.
But the big breakthroughs came a few decades later, starting with discoveries in genetics. Over the past century, an improved understanding of genetics has generated a far more robust framework for understanding how evolution works. Recent fossil discoveries, as well as better technologies for dating rocks, have vastly improved our understanding of the history of life. This is not surprising; on the contrary, it would be odd if someone writing more than 150 years ago had understood everything and entirely anticipated modern biology.
When Daniel Duzdevich first mentioned to me that he was putting On the Origin of Species into modern English, my first reaction was Really? Do you think it needs it? Chaucer, sure. But Darwin? Is he really that incomprehensible? On rereading and reflection, I concluded that the answer is often, yes.
To be sure, parts of the Origin are brilliant – lucid, clear, fascinating. Darwin is excellent at description; his best writing is when he is reporting the results of his experiments, or writing about subjects he understands well, such as the fossil record. He is sometimes eloquent, even passionate; the final chapter, where he brings all of his powers of persuasion to bear, is a triumph of rousing advocacy. But in other places he is plodding and opaque; the chapter on hybridism, for example, can defeat the most eager biologist.
He is, unsurprisingly, at his worst when writing about technical subjects he does not understand well or lacks the vocabulary to discuss. The obvious example is genetics; here, his writing is especially tortured and hard to follow. But it is easy to see why. He was writing about a subject that had not been developed yet – the word “gene” was not coined until early in the twentieth century – and his grasp of how traits are inherited was foggy. This fog shrouds his prose on the subject. It’s a pity he starts the book with genetics; many readers have surely been discouraged because the opening pages are so turgid.
But perhaps the chief reason that Darwin’s prose is difficult is that it is a kind of high Victorian writing. His sentences are often long, astonishingly convoluted, and sometimes digressive. From a modern standpoint, they also have peculiar punctuation. Add to that some archaic turns of phrase, and it’s easy to struggle.
Duzdevich is not the first to try to address these problems. In his book Almost Like a Whale (that was the original British title; in the United States the book was published as Darwin’s Ghost), geneticist Steve Jones imagined the text Darwin might have produced if he were writing now, with a modern knowledge of biology. Jones kept the same chapter structure and included some of Darwin’s original text in facsimile, but the book is nonetheless a radical reinvention of the original. James Costa, an evolutionary biologist, took a more orthodox approach and produced an annotated Origin, but while the annotations greatly help the reader to understand the background to Darwin’s thinking, they do not make the text any easier. Still another approach has been taken by Mark Ridley, also an evolutionary biologist,
