The Edge of Evolution: The Search for the Limits of Darwinism is a 2007 intelligent-design book by Discovery Institute fellow Michael Behe, published by The Free Press. Behe argues that while evolution can produce changes within species, there is a limit to evolution's ability to generate diversity; this limit, which he calls the "edge of evolution," lies somewhere between the species and order levels. On this basis he argues that known evolutionary mechanisms cannot account for all observed diversification since the last universal ancestor and that intervention by an intelligent designer could adequately explain much of life's diversity. It is Behe's second intelligent-design book; his first was Darwin's Black Box. While the book was well received by creationists and some non-biologists, many scientists—particularly biologists—have been highly critical of Behe's methods, evidence, and conclusions. Behe begins by observing that the theory of evolution comprises three related ideas—common descent, natural selection, and random mutation. He says he accepts common descent and natural selection without question but questions the scope and power of random mutation to produce beneficial changes that lead to novel, useful structures and processes. He uses the term "Darwinian evolution" to denote evolution that relies on all three of the factors and labels scientists who regard it as the only form of evolution "Darwinists"; he says they take exception to intelligent design and to other theistic and non-theistic complexity theories. Behe's central claim is that Darwinian evolution exists but is better at modifying existing metabolic pathways (or "molecular machinery") than creating new ones, and therefore plays only a limited role in the development and diversification of life. He examines genetic changes in the Plasmodium (malaria parasite) and human genomes as they respond to each other's defenses, describing the situation as "trench warfare, not an arms race." He contrasts this hemoglobin-destroying, protein-pump-compromising "war by attrition" with the "creative process" required to develop complex structures such as the bacterial flagellum and highly complex systems like the immune system. Behe calculates the "edge of evolution"—the point at which Darwinian evolution ceases to be an effective agent of creative biological change—by considering the number of mutations needed to move from one genetic state to another and the population size of the organism. He concludes that purposeful design plays a major role in developing biological complexity by producing non-random mutations that are then sculpted by natural selection. Design favoring intelligent life, he argues, is supported not only by recent findings about biological complexity but also by discoveries in chemistry (for example, the life‑supporting structure of water) and in cosmology (the anthropic principle). He strongly defends common descent for all life on Earth, including a common ancestor for humans and chimpanzees, and says the evidence is so overwhelming it should be obvious, even "trivial." Behe contends that the mutations required to bridge higher taxonomic levels are impossible without design—what he calls the "edge of evolution"—arguing that the probability of multiple simultaneous beneficial mutations is extremely low and that vast numbers of microbes have produced little in the way of new proteins or binding sites. He acknowledges that his support for intelligent design is a minority view within the scientific community. He implies that, for this reason, he avoids detailed discussion about the nature of life's designer and takes deliberate steps to distinguish himself from the Young Earth creationism movement. Reviews by scientists, especially biologists, have been highly critical: many rejected Behe's methods, evidence and conclusions, although some creationists and a few biologists were more positive. Richard Dawkins of the University of Oxford reviewed the book, focusing on Behe's claim that random mutation, rather than nonrandom natural selection, is the driving force behind evolution. Dawkins disputed Behe's assertion that no amount of random mutation could produce today's biological diversity, citing examples of selective breeding. He also argued that Behe had failed to engage with the relevant scientific research, that his work would not pass peer review in a scientific journal, and that he had bypassed peer review by publishing a popular book aimed at the general public rather than a scientific audience. Prominent biologists writing in The New Republic, Science and Nature made similar points, noting that Behe accepts much of evolutionary theory but replaces random mutation with guided mutations by an unnamed designer. Other reviewers criticized Behe for quote mining, failing to offer a theory of intelligent design despite the ten years since Darwin's Black Box, asserting a contradiction between design and "unbroken natural law," proposing an erroneous model, and ignoring publications and data that contradict his claims. Specific criticisms included using irrelevant calculations as sources, asserting that simultaneous mutations are necessary when evidence supports cumulative mutations, and neglecting the scientific literature on protein evolution. Michael Ruse, professor of philosophy at Florida State University, wrote that the book offered no developments beyond Darwin's Black Box, repeated earlier arguments, and dismissed opposing views without analysis; others expressed similar views.