Why Evolution Is True


Jerry Coyne
2009

Anyone who can read Why Evolution Is True and still doubt the reality of evolution simply is incapable of being swayed by evidence. The book is that good.

Why Evolution Is True is clearly organized into short, understandable sections — for example, island evolution is treated by first distinguishing between continental and oceanic islands, then explaining with copious examples the similarities and differences between their evolutionary histories. Why do continental islands (which were once connected to a nearby land mass) typically have native mammals, amphibians, and freshwater fish, while oceanic islands typically do not? Why does the answer support evolution rather than creation?

Every key question is answered with minimum jargon and maximum straightforwardness. Every creationist and intelligent design objection is anticipated and answered directly, with little of the scorn and condescension that plague the writing of some of Coyne’s anti-religious friends.

Frankly, Coyne’s consistently calm and rational tone surprised me, for he can be a sharp and shrill opponent when provoked. It’s evident that for the book Coyne has consciously adopted a more measured tone — and thereby a more effective manner of presentation.

The case for evolution is well-known, as are both the standard creationist objections (micro- vs. macroevolution, blood clotting, the eye, the bacterial flagellum, etc.) and their answers. There’s no need to go into the argument in any detail here. If you want to go over the case point by point, just read Coyne’s book.

Coyne’s approach to the creation vs. evolution question is  simple and convincing. Like all good scientists, Coyne asks again and again which version of the story of life better fits the evidence, and which version makes more successful predictions about future findings. In every case, evolution does a better job of explaining what we observe, and a better job of predicting what we find when we fill in gaps in our previous knowledge.

Where he is most interesting to veterans of the evolution wars is in his discussions of the scientific method and how it applies to the “big question” of human origins.

The first and most common question is “Isn’t evolution just a theory?” The use of the word “just” signals a fundamental misunderstanding. As Coyne writes:

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. … [T]he theory of evolution is more than just the statement that “evolution happened”: it is an extensively documented set of principles.

A scientific theory has a second key feature: “To be considered scientific, it must be testable and make verifiable predictions. That is, we must be able to make observations about the real world that either support it or disprove it.” A scientific theory is considered “true” when “so much evidence has accumulated in its favor—and there is no decisive evidence against it—that virtually all reasonable people will accept it.”

Crucially, Coyne continually re-emphasizes the point that “in the process of becoming truths, or facts, scientific theories are usually tested against alternative theories. After all, there are usually several explanations for a given phenomenon. Scientists try to make key observations, or conduct decisive experiments, that will test one rival explanation against another.” It is this process, comparing the explanations and predictions which derive from competing theories, which yields scientific “truth.” In time, with enough evidence, a “theory” is accepted as “fact”:

We can say, then, that evolution was a theory (albeit a strongly supported one) when first proposed by Darwin, and since has graduated to “facthood” as more and more supporting evidence has piled up. Evolution is still called a “theory,” just like the theory of gravity, but it’s a theory that is also a fact.

Throughout Why Evolution Is True, Coyne follows the methodology, asking “What results should we expect if evolution is true?” He compares these theoretical expectations to the evidence, then repeats the process with the expectations raised by creationism. In every case, without exception, with evidence from every discipline from biogeography to molecular chemistry, the physical results support evolution. He makes a thorough and devastating case for the reality of evolution and the purely speculative — and factually inadequate– nature of creationist ideas. Coyne puts the methodology this way:

So how do we test evolutionary theory against the still popular alternative view that life was created and remained unchanged thereafter? By predictions, I don’t mean that Darwinism can predict how things will evolve in the future. Rather, it predicts what we should find in living or ancient species when we study them.

Each source of evidence is examined in detail. As an example, here’s just one, short section, from Coyne’s explanation of the imperfection of evolved life:

There’s a real difference in what you expect to see if organisms were consciously designed rather than if they evolved by natural selection. Natural selection is not a master engineer, but a tinkerer. It doesn’t produce the absolute perfection achievable by a designer starting from scratch, but merely the best it can do with what it has to work with. … Ironically, it is in [its] imperfections … that we find important evidence for evolution.

evolutionary change, even of a major sort, nearly always involves remodeling the old into the new. The legs of land animals are variations on the stout limbs of ancestral fish. The tiny middle ear bones of mammals are remodeled jawbones of their reptilian ancestors. The wings of birds were fashioned from the legs of dinosaurs. And whales are stretched-out land animals whose forelimbs have become paddles and whose nostrils have moved atop their head.

There is no reason why a celestial designer, fashioning organisms from scratch like an architect designs buildings, should make new species by remodeling the features of existing ones. Each species could be constructed from the ground up. But natural selection can act only by changing what already exists. It can’t produce new traits out of thin air.

This idea, that evolution is “messy,” argues against any reasonable counter-explanation by creationists. However, that doesn’t mean that they don’t try. They go so far as to create a capricious, trickster God, who purposely designed life to give the false appearance that evolution happened. This conceptual and moral backbreaker can be found in the writing of ID superstar Michael Behe, who wrote that “features that strike us as odd in a design might have been placed there by the Designer for a reason— for artistic reasons, for variety, to show off, for some as-yet-undetectable practical purpose, or for some unguessable reason—or they might not.”

At this point, I expected Coyne to snap back into attack mode and to reel off a few paragraphs of his trademark scorn, pointing out that brain-bending statements like this one are simply meaningless in science — how could such an idea be tested? — but he restrained himself. He responded with commendable calmness:

But this misses the point. Yes, a designer may have motives that are unfathomable. But the particular bad designs that we see make sense only if they evolved from features of earlier ancestors. If a designer did have discernible motives when creating species, one of them must surely have been to fool biologists by making organisms look as though they evolved.

Some creationists argue that life is just too complicated not to have been designed. In contrast, Coyne points out that natural selection is economical and effective:

The process is remarkably simple. It requires only that individuals of a species vary genetically in their ability to survive and reproduce in their environment. Given this, natural selection—and evolution—are inevitable. … [T]his requirement is met in every species that has ever been examined.

At most, a creationist might hang on to the belief that this “remarkably simple” process required a divine creative mind to imagine it and then put it into place. This belief, unlike the denial of the reality of evolution, isn’t obviously and evidently wrong.

There’s no real case for this view, and there’s no logic supporting the addition of an unnecessary supernatural first step. But at least, with this limited assertion, creationism stays in the speculative realm where it belongs.

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