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1.1 Life before Darwin
God made the world. He made light and darkness, sun and moon, land and water. He made the different kinds of plants and animals and instructed them to breed according to their kind. He finally arrived at the pinnacle of all creation, man and woman. He gave them stewardship over the earth and commanded them to populate the globe.
The world, in return, spoke of God’s existence and his attributes. Jesus could tell a parable about a wildflower’s ornamentation, to illustrate God’s goodness, his generosity, his wisdom and power, and his rapt audience could understand everything he said. They already grasped, without having to be told, that God designed the world to reveal, in symbolic form, his inner nature.
The world spoke of the darker aspects of God’s creation, too. Nature spoke of our disobedience and sin, our distance from God, our need for a redeemer. A swarm of locusts decimates crops and plunges a community into starvation. A pride of lions slowly tears apart a hyena. People suffer and die from inexplicable diseases, diseases that never should have arisen, that were never part of God’s original plan.
At some point in the eighteenth and nineteenth centuries—it’s hard to say just when—God began to abandon us. Or we began to abandon him. We increasingly distanced ourselves from God, pushed him to the outskirts of the universe, both in space and in time. His pervasive presence was no longer felt as an irrefutable fact, but as something that needed to be proven by clever arguments. Charles Taylor has labeled this process “secularization.”1 The sciences of nature and life were drivers of this “secularization,” and shaped by it, too.
Half a century before Charles Darwin began writing, students of nature began to hold forth that the earth was not of recent origin, but it was very ancient, contrary to the teachings of Genesis. Earth scientists like James Hutton and Charles Lyell argued that the great land masses of the earth, its canyons and mountains, the distribution of kinds of animals across the planet, weren’t caused by a global flood that God sent several thousand years ago to punish our wickedness. They were formed over millions of years by slow, stubborn, mindless, laws of nature. (This was Lyell’s uniformitarianism, which stood in stark contrast to the catastrophism of thinkers like Georges Cuvier, who saw natural landscapes as products of cataclysmic upheavals on the order of Noah’s flood.) Over the eons, a trickle of water becomes a ravine, which becomes a raging river. Great canyons form by the steady accumulation and compaction of sediment.
Students of the living world began to wonder, too, whether the diversity of plants and animals around us could have arisen in a gradual way, through the slow working out of the laws of nature, and not through an instantaneous, supernatural act of creation. Thus could Erasmus Darwin, Charles Darwin’s grandfather, write poetically of the transmutation of one species into another. Could some kinds of animals have actually emerged from other kinds of animals by a mindless process? Is it possible that, long ago, God made one or a few basic prototypes, single-celled animals, and that they began to diversify, to change, and over the generations, evolve into the panoply of creatures that we see today? Could we have arisen out of that very same process?
When Erasmus Darwin was writing, evolution was still part of the scientific fringe. That is because it didn’t have a mechanism, a how. How exactly could one species come out of another? Early theorists, like Étienne Geoffroy Saint-Hilaire, pointed vaguely to how the “conditions of life” shape the appearance of a species. Toiling daily in the hot sun, or being malnourished for long periods of time, leave their direct imprint on our bodies. People living in different environments would have different such imprints. But surely, the “conditions of life” alone don’t have the power to generate the bewildering diversity of living forms that surround us.
One of the first serious attempts to describe an actual mechanism of evolution was due to the French scientist Jean-Baptiste Lamarck, with his famous inheritance of acquired characteristics. Suppose a giraffe wishes to reach a patch of leaves high above its head. It experiences a new need, a besoin, which causes it to stretch its neck as far as it can. Through repeated stretching, its neck lengthens somewhat, and those acquired changes are somehow funneled down through the generations, through its sperm and egg. Its descendants would have longer necks than the descendants of those who never strove for the higher leaves. A species would slowly change over time in response to the challenges of its environment. But evolution remained a speculative doctrine.
Evolution only became a serious scientific theory with the advent of a believable mechanism. Two scientists, Charles Darwin and Alfred Russel Wallace, solved the problem. They envisioned a new mechanism, one that, in their view, would not replace the inheritance of acquired characteristics, but supplement it. This is the law of natural selection, or nature’s selection, in contrast to artificial selection, the kind that people engage in when they breed animals for beauty or utility. Darwin and Wallace’s discovery transformed not only the science of nature, but the study of mind. For it suggested that minds, too, emerged gradually through the very same process that gave rise to hearts, lungs, and legs, and for much the same reason, as tools to help us survive on this planet.
1.2 Nature’s selection
What is natural selection? Natural selection is not the same thing as evolution. Evolution is any kind of change, more or less permanent, in a species. Natural selection is one of the main motors of evolution. It is a how of evolution.
Sometimes, due to chance—nature’s “sports,” as Darwin put it—the creatures in a population differ from one another. A polar bear is born with a longer snout, or sharper teeth, or faster running speed. (We now know that many of these variations are due to random gene mutations.) Some, perhaps most, of these “sports” would be extremely devastating—a single gene mutation gives rise to the tragedy of cystic fibrosis, or muscular dystrophy. But in some rare cases, they might yield a slightly superior design.
That difference, that superior design, would give the bear a slight edge in the struggle for existence. That bear would run more quickly, kill more effectively, and secure a larger provision of meat, than its competitors. On average, it would live longer and sire more cubs than the bears lacking this new quality. Over time, and assuming that like begets like, this new kind of bear-design would gradually spread through the population. That is change. That, too, would be evolution. I’ll return shortly to develop the details of their theory.
The real beauty of the theory of natural selection is the way that Darwin and Wallace were able to assemble a handful of well-known facts about the natural world into a powerful explanation for how species change. The basic ingredients of the theory—that members of the same species differ slightly from one another, that those differences could spell relative success or failure, that like begets like—had been recognized for millennia. The breeding experiments described in the book of Genesis, in which Jacob exacted just retaliation against Laban for his stinginess, show a clear grasp of these very principles. But nobody had put them together in quite that way before.
It might seem strange that two different people—almost complete strangers, at that—came up with the exact same theory. In another sense, it isn’t so strange, given that Darwin and Wallace were products of the same intellectual climate, the same social and political upheavals, the same restless questioning of the ancient creationist creed. In particular, both Darwin and Wallace were profoundly influenced by the rather pessimistic theories of an English political scientist, Thomas Malthus, and his idea of the struggle for existence. Their thinking was also shaped by other major movements in the life sciences, such as Lyell’s uniformitarianism.
In short, Malthus’ gloomy proposal was this: in human society, there will always be want. There will always be need. There will always be poverty, and starvation, and competition. That is because human beings are driven by two incompatible desires: the desire for food and the desire for sex. People like to eat and they like to have sex. But when they have sex, they drive population growth—and eventually run out of food. A bit of mathematical reasoning convinced Malthus that the problem was insoluble. Hence the necessity of poverty, starvation, early death. Malthus railed tirelessly against the social welfare programs of his day, programs that, in his opinion, only encouraged the poor to have more children and thereby perpetuate their miserable state.
Malthus’ struggle for existence was mainly intended to describe human society, but he noticed, in passing, that the struggle for existence would apply to animals, too. What Darwin and Wallace did—again, quite independently of one another—was to recognize the struggle for existence as a basic principle of life on earth. All life is involved in a brutal competition for continued life. In one of the most famous passages in Darwin’s corpus, he tells us bluntly:
Nothing is easier than to admit in words the truth of the universal struggle for life, or more difficult—at least I have found it so—than constantly to bear this conclusion in mind. Yet unless it be thoroughly engrained in the mind, I am convinced that the whole economy of nature, with every fact on distribution, rarity, abundance, extinction, and variation, will be dimly seen or quite misunderstood. We behold the face of nature bright with gladness, we often see superabundance of food; we do not see, or we forget, that the birds which are idly singing round us mostly live on insects or seeds, and are thus constantly destroying life; or we forget how largely these songsters, or their eggs, or their nestlings, are destroyed by birds and beasts of prey; we do not always bear in mind, that though food may be now superabundant, it is not so at all seasons of each recurring year.2
The principle of natural selection isn’t just the application of the struggle for existence to the rest of life. After all, the idea of natural selection never occurred to Malthus. Darwin and Wallace’s pivotal realization was that starvation, malnutrition, and early death do not befall all members of a population equally. These woes are unevenly doled out. Scrub jays with sharp memory will likely survive the winter better than those with poor memory, since they can better remember where they hid their food. Deer mice with lighter fur can hide more easily in the Nebraska Sandhills than their darker siblings, and thereby better escape predation by hawks. In general, if any creature possesses a distinctive trait, or phenotype, that gives it an edge in the struggle for existence, and if this trait can be faithfully passed on from parent to offspring, then the trait should spread through the population.3
Darwin came up with the term “natural selection” to evoke an analogy to the practice of breeding animals: artificial selection. He spent an extraordinary amount of time with pigeon breeders, and was impressed by the way that breeders “select” desirable traits of domestic animals, often with dramatic effects. In fact, artificial selection is so powerful that it was often hard for people to decide whether two different breeds of pigeon were actually modified representatives of one and the same species, rather than two quite separate species, each created uniquely by God. Isn’t it possible that nature, too, “selects” desirable traits in its creatures? “As man can produce and certainly has produced a great result by his methodical and unconscious means of selection, what may not nature effect?”4 The difference is that nature only selects for traits that give the creature an edge in the struggle for existence, rather than for human usefulness or attractiveness.
1.3 Sexual selection
Animals don’t just compete with one another for survival. After all, even if you survive well, but you’re terrible at finding mates, then you won’t leave any progeny to carry your design features into the future (unless you happen to be good at asexual reproduction, like starfish or whiptail lizards). Cynical as it sounds, the number and quality of potential sexual partners is itself a limited resource, much like food or shelter. The members of one sex must compete with each other for mating opportunities with the other sex. There is no way around this unpleasant fact. “Sexual selection” describes this competition. Sexual selection isn’t something different from natural selection. Ra...
