Most people, when they contemplate the living world, conclude that it is a designed place. So it is jarring when biologists come along and say this is all wrong. What most people see as design, they say - purposeful, directed, even intelligent - is only an illusion, something cooked up in a mind that is eager to see purpose where none exists. In these days of increasingly assertive challenges to Darwinism, the question becomes acute: is our perception of design simply a mental figment, or is there something deeper at work? Physiologist Scott Turner argues eloquently and convincingly that the apparent design we see in the living world only makes sense when we add to Darwin's towering achievement the dimension that much modern molecular biology has left on the gene-splicing floor: the dynamic interaction between living organisms and their environment. Only when we add environmental physiology to natural selection can we begin to understand the beautiful fit between the form life takes and how life works. In "The Tinkerer's Accomplice", Scott Turner takes up the question of design as a very real problem in biology; his solution poses challenges to all sides in this critical debate.