Book excerpt: Much of the evolutionary debate since Darwin has focused on the level at which natural selection occurs. Most biologists acknowledge multiple levels of selection—from the gene to the species. The debate about group selection, however, is the focus of Mark E. Borrello’s Evolutionary Restraints. Tracing the history of biological attempts to determine whether selection leads to the evolution of fitter groups, Borrello takes as his focus the British naturalist V. C. Wynne-Edwards, who proposed that animals could regulate their own populations and thus avoid overexploitation of their resources. By the mid-twentieth century, Wynne-Edwards became an advocate for group selection theory and led a debate that engaged the most significant evolutionary biologists of his time, including Ernst Mayr, G. C. Williams, and Richard Dawkins. This important dialogue bled out into broader conversations about population regulation, environmental crises, and the evolution of human social behavior. By examining a single facet in the long debate about evolution, Borrello provides powerful insight into an intellectual quandary that remains relevant and alive to this day.