with rare exceptions (chiefly the social insects), mammals and birds are the only organisms to devote substantial attention to the care of their young; an evolutionary development that, through the long period of plasticity which it permits, takes advantage of the large information-processing capability of the mammalian and primate brains. Love seems to be an invention of the mammals.
Carl Sagan, Dragons of Eden: Speculations on the Evolution of Human Intelligence
brain, brain-plasticity, human-evolution, intelligence