ABSTRACT
In reviewing mammalian behavior, the authors begins by considering the role of one great instinct, Nature's brightest and most beautiful invention, the parental instinct. The parental instinct of the higher mammals shows that lack of specificity which characterizes all their instincts. Among the mammals instinct is part of the natural endowment of the female sex in all species; for the suckling of the young is its simplest and primary expression, without which the mammary glands would be useless and the young could not live. In the mammals the instinct is less specialized, conforming in respect to the general rule; but in the lower mammals and in many birds we observe such a degree of specialization that the animal may starve to death in the midst of plenty, through lack of adaptability of the instinct. The higher mammals show but little specialization and hence considerable adaptability.
