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Second, his critics argued that intelligent design, whatever its merits, is not science. Even Behe's colleagues at Lehigh University, where he teaches, seem embarrassed by his position. The biology department mission statement on its website reads, "It is our collective position that intelligent design has no basis in science, has not been tested experimentally, and should not be regarded as scientific." This is bad philosophy of science, if not poor collegiality, because many theories in science are not experimentally testable in any straightforward fashion. The role of luck in evolution is itself a matter of very abstract statistical debate.

Darwin's Black Box focused on specific cases of what he called irreducible complexity. Critics picked apart his examples like vultures on carrion. The Edge of Evolution more carefully and more comprehensively focuses on evolutionary processes at the level of molecular biology.

Much of this book tells the fascinating story of the epochal battle between the human and malarial genomes. Darwinians are fond of using the metaphor of an arms race to describe evolution. In an arms race, each side (predator and prey) responds to the other by improving their position, which means that their relative positions remain the same, even as their individual performances improve. Gazelles that run the fastest will pass more of their genes along to the next generation, for example, resulting in faster gazelles overall, but the lions that chase them will do the same thing. Darwinians use this metaphor to illustrate how species advance even as their role in the predator-prey scheme remains the same.

But what if the struggle of life looks more like trench warfare than an arms race? In trench warfare, anything goes for immediate gain. Species fight each other without any lasting improvements in their biological structures. "If the enemy can be stopped or slowed by burning your own bridges and bombing your own radio towers and oil refineries, then away they go. Darwinian trench warfare does not lead to progress — it leads back to the Stone Age." This is exactly what happened in our attempt to disarm malaria. When chloroquine was first made widely available, it slowed down the spread of this tropical disease, but the malarial parasite soon evolved an effective defense against the drug. However, this battle did not result in a new and improved malarial cell. Instead, when chloroquine was no longer a threat, malaria reverted to its old ways. Its protective mutations deteriorated; they did not create anything new.

Behe admits that mutations can result in biological advances when organisms adapt to their environment by taking tiny, incremental steps. When larger steps are needed, however, evolution does not have a chance. Changes at the molecular level require long jumps that cannot be traversed by random mutations. Behe locates the limits of evolution in the length of these steps. "The more intermediate evolutionary steps that must be climbed to achieve some biological goal without reaping a net benefit, the more unlikely a Darwinian explanation." When organisms need to move forward in relatively brief time spans, they are more likely to stumble than advance. Or, as in the case of malaria, any successful step they take is just as likely to be followed by a step backward as by any forward progress.

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March (Web-only) 2008, Vol. 52