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Science requires of itself a high burden of proof. Origin-of-life discussions often begin with Stanley Miller’s recreation of the primordial earth in the laboratory. Complete with lighting, heat, and a slurry of simple elements, Miller’s small, flask-ensconced world eventually did bear elementary organic molecules. But in science, showing that an event is possible is not the same as describing what really happened. Every hypothesis, every notion must be internally consistent, supported by everything that’s come before it. And every theory must allow for the possibility of rejection. Failure is a way of life. Newton saw what he saw, but Einstein was able to see more because data on light and space had taken our physical conclusions outside the realm of everyday experience.

Darwin discovered natural selection at the level of morphology, but only after DNA was discovered as the vector for heredity did people like Theodosius Dobzhansky, Ayala’s mentor, find that evolution is actually a statistical change in the frequency of a given gene in a larger gene pool.

Science is always correcting itself, building itself up. And occasionally, during periods of great scientific debate and change, outsiders will pick up on an open contradiction, where data has not yet coalesced.

In the Texas debate on “strengths and weaknesses,” the group of social conservatives was pressed on what a possible “weakness” might be. What might they teach in the classroom that would subvert what seems to be a solid consensus? In response, Texas Board of Education Republican Barbara Cargill alluded to a recent January 2009 cover of the New Scientist magazine, which proclaimed, “Darwin was Wrong.” It wasn’t clear that she read the article, or that she understood the basis of the cover. But the words were bold. They were superimposed on an image of a gnarled tree, strangely evocative of the famous one in biblical Eden.

One of Darwin’s fundamental ideas was the existence of a tree of relatedness describing all living things. Ayala includes a number of trees in his discussion of missing links, like Archaeopteryx between dinosaurs and birds, and Tiktaalik between fish and amphibians. You’ve perhaps seen the tree of life on the T-shirts of young urbanites, an image that has the power to be a secular counter to the Jesus fish. Darwin wrote in one of his notebooks the words, “I think,” followed by a cartoon evolutionary tree—the first of its kind—that showed species-spokes radiating from ancestor nodes. The tree represented nothing solid, but was one of the culminating abstractions of Darwin’s fieldwork, the kind of insight that offers itself up as a general principal only after decades with your hands in the mud.

This tree concept is now under attack from within science. Recent advances in molecular evolution and bioinformatics have shown that species don’t only evolve vertically from ancestor to descendant, as Darwin had postulated, but instead evolve laterally, with DNA exchanges between unrelated individuals. This kind of horizontal gene transfer is rampant among bacteria, smearing vertical signals and blurring the simple clarity of Darwin’s original insight. The question now is whether the tree metaphor is too simple to encompass the complexity of gene exchange. Iconoclasts within the field are calling for new images, new metaphors: web of life, an evolutionary thicket.

But none of this is actually an assault on Darwin’s core concepts, concepts that Ayala lays out with care. In evolution there is no grand plan, only mechanism. Natural selection still operates on organisms regardless of how their genetic changes accumulate. The strong still survive to populate the earth and the weak give up their niches. We do arise from monkeys.

The New Scientist’s inflammatory cover was a misrepresentation of the article it actually published. In a bewildered, angry response to the editors, a group of scientists and philosophers of science led by Daniel Dennett and Richard Dawkins wrote that “evolution’s base is heredity; heredity generates hierarchy, hence evolution generates hierarchy.” Despite the miasma of horizontal transfer, specks of a tree remain. “Of course there’s a tree; it’s just more of a banyan than an oak at its single-celled organism base.”

The explication of this new observation wasn’t the issue. The issue was how the ideas were framed. Darwin was not wrong, but a headline often matters more than the article from which it’s distilled. In a world blinkered by the culture wars and their politics, the New Scientist cover was perfect fodder for anti-evolutionists regardless of what it was actually describing. A large scientific concept in potential transition is tempting to both journalists and fundamentalists alike. In its willingness to fail, science opens itself to manipulators of all stripes. Dawkins and company anticipated the damage “done by creationists parlaying [the New Scientist’s] reputation into propaganda.” And that’s exactly what Cargill did.

Ayala ends his book with awe for nature. Despite his religious indulgence, he is a scientist after all. He muses that if God had engineered out all catastrophe we’d be left with an ideal but colorless world. This world “would not be a creative universe, where galaxies form, stars and planetary systems come about, and continents drift. The world that we have is creative and more exciting than astatic world.” I like that idea. In a creative universe, one without orchestration, evolution is capable of great violence. Entire lineages rise and fall in a geological nanosecond. Life improvises, sometimes haphazardly.