Lisa Reinoehl, age 9, of Stratford, Conn., for her question:

WHAT ARE INSTINCTS?

Invertebrate animals, such as worms and insects, are more completely governed by instincts than are higher vertebrate animals, which adapt to their environment through some kind of learned behavior. The higher and more intelligent the animal, the greater is his capacity to learn. Man, having learned the basics of how to survive, has kept on learning.

Instinct is behavior that is inherited rather than learned. Instinct and instinctive behavior are terms used by scientists to describe activity that involves neither experience nor learning.

For a behavior trait to be truly instinctive, it must be typical of almost all members of at least one species of animal.

All animals perform certain instinctive actions and learned actions. Insects and crustaceans, such as crabs and lobsters, can learn only a little, so they depend almost completely on instincts to survive. The higher you go on the animal scale, the more it can learn and the less it will have to depend on instinct.

A baby chick, for example, will freeze motionless when any object appears near him. Instinctively, he will not move even if a leaf falls near him. Older chickens, on the other hand, have learned that a falling leaf cannot hurt them, so they do not react as they did when they were young. Learning has taken over for an instinct.

Fish depend more on instinct than birds, and birds depend on instinctive action more than mammals. In the human family, a baby will smile and suck instinctively, but as he grows older, most of his acts are learned.

For the most part, however, humans appear to have few or no instinctive patterns. Sucking and smiling as infants, for example, are considered,to be reflexes by some scientists, and not instincts.

At one time in the past, scientists told us that tendencies toward many types of behavior were inborn and were passed from generation to generation. In modern times, however, experiments have shown that most human behavior is the result of maturation and learning.

In psychiatry, the term instinct denotes the innate biological drives and motivations necessary to fulfill human needs for oxygen, water, food, maintenance of body temperature and the avoidance of physical injury.

Secretion of hormones plays a part in the instinct picture with some animals. A change in secretions will tell a bird when to migrate. If the gland does not secrete a certain hormone properly, an animal may not be able to carry out his instinctive behavior that is associated with the hormone.