Why Evolution Is True

by Jerry A. Coyne

The truth—that we, like lions, redwoods, and frogs, all resulted from the slow replacement of one gene by another, each step conferring a tiny reproductive advantage—is surely more satisfying than the myth that we were suddenly called into being from nothing.

Evolution is like an architect who cannot design a building from scratch, but must build every new structure by adapting a preexisting building, keeping the structure habitable all the while.

So natural selection does not yield perfection—only improvements over what came before. It produces the fitter, not the fittest.

First, in science, a theory is much more than just a speculation about how things are: it is a well-thought-out group of propositions meant to explain facts about the real world.

All scientific truth is provisional, subject to modification in light of new evidence.

Over the first 80 percent of the history of life, all species were soft-bodied, so we have only a foggy window into the earliest and most interesting developments in evolution, and none at all into the origin of life.

If the entire course of evolution were compressed into a single year, the earliest bacteria would appear at the end of March, but we wouldn’t see the first human ancestors until 6 a.m. on December 31. The golden age of Greece, about 500 BC, would occur just thirty seconds before midnight.

What we see in bird evolution is the refashioning of old features (forelimbs with fingers and thin filaments on the skin) into new ones (fingerless wings and feathers)—just as evolutionary theory predicts.

A trait can be vestigial and functional at the same time. It is vestigial not because it’s functionless, but because it no longer performs the function for which it evolved.

We humans have many vestigial features proving that we evolved. The most famous is the appendix.

In other words, our appendix is simply the remnant of an organ that was critically important to our leaf-eating ancestors, but of no real value to us.

Out of about thirty thousand genes, for example, we humans carry more than two thousand pseudogenes.

Perfect design would truly be the sign of a skilled and intelligent designer. Imperfect design is the mark of evolution; in fact, it’s precisely what we expect from evolution.

A smart designer wouldn’t put a collapsible tube through an organ prone to infection and swelling. It happened this way because the mammalian prostate gland evolved from tissue in the walls of the urethra.

Again one must ask: If animals were specially created, why would the creator produce on different continents fundamentally different animals that nevertheless look and act so much alike?

Species that live in similar habitats will experience similar selection pressures from their environment, so they may evolve similar adaptations, or converge, coming to look and behave very much alike even though they are unrelated. But these species still retain key differences that give clues to their distant ancestry.

Selection is not a mechanism imposed on a population from outside. Rather, it is a process, a description of how genes that produce better adaptations become more frequent over time.

The evolution of resistance creates an arms race between humans and microorganisms, in which the winners are not just bacteria but also the pharmaceutical industry, which constantly devises new drugs to overcome the waning effectiveness of old ones.

And each time a mystery is solved, ID is forced to retreat. Since ID itself makes no testable scientific claims, but offers only half-baked criticisms of Darwinism, its credibility slowly melts away with each advance in our understanding.

If the history of science teaches us anything, it is that what conquers our ignorance is research, not giving up and attributing our ignorance to the miraculous work of a creator.

We can’t see the Grand Canyon getting deeper, either, but gazing into that great abyss, with the Colorado River carving away insensibly below, you learn the most important lesson of Darwinism: weak forces operating over long periods of time create large and dramatic change.

Remember that the currency of selection is not really survival, but successful reproduction. Having a fancy tail or a seductive song doesn’t help you survive, but may increase your chances of having offspring—and that’s how these flamboyant traits and behaviors arose.

The evolutionary difference between males and females is a matter of differential investment—investment in expensive eggs versus cheap sperm, investment in pregnancy (when females retain and nourish the fertilized eggs), and investment in parental care in the many species in which females alone raise the young. For males, mating is cheap; for females it’s expensive.

Selection then favors genes that make a male promiscuous, relentlessly trying to mate with nearly any female.

Preferences aren’t always a matter of random inborn taste, as Darwin supposed, but in many cases probably evolved by selection.

Using the reproductive criterion for species status, Mayr defined a species as a group of interbreeding natural populations that are reproductively isolated from other such groups.

It’s important to realize that species don’t arise, as Darwin thought, for the purpose of filling up empty niches in nature. We don’t have different species because nature somehow needs them.

Speciation is like separating oil and vinegar: though striving to pull apart, they won’t do so if they’re constantly being mixed.

I am aware that the conclusions arrived at in this work will be denounced by some as highly irreligious; but he who denounces them is bound to shew why it is more irreligious to explain the origin of man as a distinct species by descent from some lower form, through the laws of variation and natural selection, than to explain the birth of the individual through the laws of ordinary reproduction [the pattern of development].

It’s likely that, due to cultural change, we are going downhill genetically in many ways. That is, genes that once were detrimental are no longer so bad (we can compensate for “bad” genes with a simple pair of eyeglasses or a good dentist), and these genes can persist in populations.

What moves science forward is ignorance, debate, and the testing of alternative theories with observations and experiments. A science without controversy is a science without progress.

The world still teems with selfishness, immorality, and injustice. But look elsewhere and you’ll also find innumerable acts of kindness and altruism. There may be elements of both behaviors that come from our evolutionary heritage, but these acts are largely matters of choice, not of genes.

Evolution tells us where we came from, not where we can go.

The fairest thing we can experience is the mysterious. It is the fundamental emotion which stands at the cradle of true art and true science. He who knows it not and can no longer wonder, no longer feel amazement, is as good as dead, a snuffed-out candle.

We are the one creature to whom natural selection has bequeathed a brain complex enough to comprehend the laws that govern the universe. And we should be proud that we are the only species that has figured out how we came to be.