Maternal Instinct A breeding female performs activities which are not only highly effective; they also seem to be both predictable and firmly fixed. Like some social signals they have been called innate or instinctive. Prominent are nest building and bring back straying young to the nest. A pregnant female reliably builds a nest from the materials available, and retrieves her young to it. Such behavior seems compelled by an internal drive, and to develop without learning by practice. But it is not. Females have been reared in cages without anything which could be picked up or manipulated. Their food was powdered and even their faeces fell through a floor of netting. At maturity, they were mated in ordinary cages and produced litters. But they did not make nests; instead they scattered nesting material around their cages. They similarly failed to retrieve their young to a single place, but carried them around without obvious direction. The deficient behavior resulted from an environment which did not offer the usual opportunities to learn how to manipulate objects. The maternal behavior of the rat provides examples of activities which are notably stable in development; but, as these findings show, they develop not in a vacuum but in an inconstant environment. Once again, to understand behavior we have to consider the dynamics of development from egg to adult. Source: the book "The Story of Rats" by S.A. Barnett