From the Scopes Monkey Trial of 1925 to the court ruling against the Dover Area School Board s proposed intelligent design curriculum in 2005, few scientific topics have engendered as much controversy or grabbed as many headlines as evolution. And since the debate shows no signs of abating, there is perhaps no better time to step back and ask: What is evolution? Defined as the gradual process by which something changes into a different and usually more complex and efficient form, evolution explains the formation of the universe, the nature of viruses, and the emergence of humans. A first-rate summary of the actual science of evolution, this "Scientific American" reader is a timely collection that gives readers an opportunity to consider evolution s impact in various settings. Divided into four sections that consider the evolution of the universe, cells, dinosaurs, and humans, "Evolution" brings together more than thirty articles written by some of the world s most respected evolutionary scientists. As tour guides through the genesis of the universe and complex cells, P. James E. Peebles examines the evidence in support of an expanding cosmos, while Christian de Duve discusses the birth of eukaryotes. In an article that anticipated his book "Full House, "Stephen Jay Gould argues that chance and contingency are as important as natural selection for evolutionary change. And Ian Tatersall makes two fascinating contributions, submitting his view that the schematic of human evolution looks less like a ladder and more like a bush. With the latest on what s being researched at every level of evolutionary studies, from prospects of life on other planets to the inner working of cells, "Evolution" offers general readers an opportunity to update their knowledge on this hot topic while giving students an introduction to the problems and methodologies of an entire field of inquiry. "