Instinct is inherited knowledge that directs the behavior of animals. Instincts ensure that an animal knows the behaviors it needs to survive and reproduce. Instinct guides such actions as building nests and digging burrows. It directs courtship and mating. It influences hibernation and migration. In fact, a wide variety of animal behaviors are directed by instinct.
An animal inherits instincts from its parents. As a result, instincts are particular to each species (kind) of animal. That is, the instincts of one species usually differ from those of another. But instinctive behaviors appear at about the same time and in the same form among the members of a particular species.
Instincts differ from learned behaviors, which develop gradually through experience. However, most behaviors involve a mix of instinct and learning. The nesting behavior of birds shows this mix of instinct and learning. Each species of bird that builds a nest does so with a particular structure, using particular materials. In fact, an expert can often identify the bird species that built a nest with just a glance at the nest’s construction. Birds that are raised in an incubator may never have seen a nest. Nevertheless, these birds generally construct a nest typical of their species the first time they feel the urge. However, the nests of most birds improve with building experience. Nests also show individual differences in the amount and proportion of building materials. These variations depend partly on learning.
A reflex, such as blinking at a bright light, is also a type of unlearned behavior. But reflex actions are less complicated than instinctive behaviors. Also, reflexes are not particular to a certain species (see Reflex action).
How instinctive behavior works.
Instincts are innate—that is, they are present in an animal even before it is born or hatches. From the moment it hatches, a bird has instinctive knowledge of how to build a nest. However, most instinctive behavior is released (brought about) by a stimulus, a cue that prompts an instinctive behavior. The stimulus is sometimes called the releaser.
For example, ground-nesting birds, such as geese and gulls, have innate knowledge of how to retrieve an egg that has rolled out of the nest. With no need for learning, the bird fixes its gaze on the egg and stands. It steps forward and places its bill on the far side of the egg. The bird then gently rolls the egg back between its legs into the nest. Finally, the bird settles back onto the nest.
The sight of an egg outside the nest is the stimulus for the bird to retrieve the egg. By placing various objects near the nest, scientists have discovered that ground-nesting birds retrieve eggs as an instinct, not through learning. For example, gulls lay eggs that are grayish to greenish-brown, with small speckles. But even an experienced gull will retrieve eggs of other colors. Gulls also retrieve tennis balls, grapefruit, and light bulbs. Any of these objects serves as a stimulus for the bird’s instinct to retrieve eggs. In fact, some objects are a more powerful stimulus for this behavior than the gull’s own eggs. Scientists have offered gulls two objects at once and recorded which one the bird retrieves first. Gulls prefer objects with larger speckles than their own eggs have. They also prefer objects that are larger than their eggs.
Instinctive behaviors can be rigid. The egg-rolling response is the same in all gulls. Gulls always use the underside of the bill to roll the egg. They never experiment with using their feet or wings. They never walk to the far side of the egg and push it toward the nest. The egg-recovery response is especially rigid in geese, which also build nests on the ground. Once the bird has begun reaching for the egg, a scientist can remove the egg as the goose watches. Nevertheless, the goose will still attempt to roll the missing egg into the nest.
Motivation.
During most of the year, gulls eat eggs rather than retrieve them. It is only when they are nesting that they have the instinct to retrieve eggs. This change in response to a stimulus is the result of a change in motivation or drive. Motivations are internal urges. These urges tell birds to migrate, to establish territories, and to build nests. Often, motivation is controlled by hormones, secretions produced mostly by glands. For example, the drive to migrate is controlled partly by hormones. The concentration of these hormones varies with the length of the day. The days grow shorter as winter approaches. This changes the concentration of hormones in migrating species, helping motivate them to fly to their winter range.
Imprinting.
Instinct also causes an interesting type of behavior called imprinting. Soon after hatching, a goose mother leads her hatchlings away from the nest with an innate call. The call and the movement prompt the goslings (young geese) to follow their mother. During the trip, the goslings hear their mother’s voice and see her appearance. This information enables them to recognize her later. In general, imprinting must take place within a critical period. For example, if it does not occur within about three days, goslings are unable to imprint on their mother. In fact, they may even flee from her.
Experiments show that geese have little innate sense of what a parent looks and sounds like. As a result, goslings can imprint on dogs, people, rubber balls, toy trains, or just about anything that moves. But they do imprint faster and stronger to adults of their own species.
Finally, imprinting is often irreversible. For example, after fully imprinting, a goose cannot imprint onto a different parent.
Human instincts.
Human beings are among the species that show great flexibility in behavior. People are less dependent on instincts than many other species are. Nevertheless, human beings do display much instinctive behavior. For example, the overwhelming drive of infants to acquire language is obvious. At a simpler level, many of our facial expressions are innate. People from different cultures can identify the emotion associated with certain facial expressions. For example, all people understand that a smile expresses happiness. Instincts may also influence certain fears. For instance, many people fear snakes. Some evidence suggests that people develop a fear of snakes more quickly than a fear of many other objects. Snakes have been a danger to people for so long that we may have developed an instinctive fear of them.
