Whenever you refer to things from an outside source (e.g., ideas, information, statistics, images, concepts, or facts), you must cite the source of this information. Additionally, you need to quote, paraphrase, or summarize material clearly and accurately.
Berger (2007) has said:
Evolutionary social scientists note that if mothers were the exclusive caregivers of each child until children were adults, able to provide for themselves and their own children, a given woman could rear only one or two offspring - not enough for the species to survive. (p. 157)