A new book that challenges the extent to which natural selection explains evolution has been attacked by biologists even though the book's authors do not contest evolution itself. "What? Attack natural selection?! Surely, Darwin arrived at an irrefutable proposition," says Cambridge professor Simon Morris. "Recruiting the Malthusian insight that a given population will always increase more rapidly than the resources available to sustain it, Darwin argued that the culling of the less fit is an inevitability and can be achieved only by the pervasive and ceaseless scrutiny of natural selection. Uncertainty that natural selection is, in fact, the real motor of evolutionary change has been a constant theme of those skeptical of Darwin’s formulation."