The primary purpose of the passage is to A. question the plausibility of one explanation sometimes offered for the dwarfing of certain species living on islands B. argue that dwarfing of certain species living on islands occurred prior to the Pleistocene C. cite evidence suggesting that dwarfing may have adverse consequences for some species living on islands D. present some possible explanations for the dwarfing of certain species living on islands E. contrast the effects of insular conditions on species with large body size and species with small body