The behavior of animals may be categorized as either innate (instinctive) or learned (associative). Innate behavior is genetically programmed into animals. Each individual inherits a suite of behaviors (an ethogram) just as they inherit physical traits such as feather color, length of tail, and number of legs.
Innate behavior is characterized as being:
1. Inheritable and since it is encoded in the DNA, it can be passed from generation to generation.
2. Inflexible since it is not modified by development or experiences.
3. Intrinsic as it is present in animals raised in isolation from others of its kind.
4. Stereotypic as it presents itself in the same way each time by each individual.
Early Studies of Geese Led the Way
Pioneering behaviorists Konrad Lorenz and NikoTinbergen noted that some behavioral patterns were so stereotypical (appearing in the same way in different individuals of the same species) that those patterns must be instinctive or innate (based on preset neural pathways). In a famous paper in 1938, they described the workings of innate behavior as it related to the egg-retrieval response of Greylag geese (Anser anser).
If an egg is disturbed from the nest, the female Greylag will rise; extend her neck until the bill is just over the misplaced egg and then bend, pulling the egg carefully back into the nest with a side-to-side motion. Although this behavior might seem intelligent and perhaps learned, Lorenz and Tinbergen noted that removing the egg once caused the goose to begin the retrieval pattern. They also noted that slipping the egg away and rolling it down the nest caused the goose to continue the retrieval motion pattern without the egg and then settle on the nest.
Realizing that the egg was still missing, the goose then repeated the entire pattern anew. Once initiated, the egg-retrieval pattern apparently had to be completed in the same fixed series of steps. Lorenz and Tinbergen concluded that such behaviors must be set in the genetic blueprint (instinctive or innate) and cause animals to show essentially the same behavior throughout their entire lives from the first time it is triggered.
Further investigations by Tinbergen demonstrated that any number of objects might trigger the egg-retrieval pattern in the Greylag goose. Geese will attempt to roll baseballs, balloons, and even beer cans back into their nests. Furthermore, once the foreign object is in the nest, the goose recognizes that they are not eggs and removes them, repeating the pattern over and over.
Innate Behavior is Triggered by a Releaser
Lorenz and Tinbergen found that any object similar to an egg outside the nest was a trigger or releaser that initiated the egg-retrieval pattern. As the animal responded to the sound, or to the shape, or to some other part of a releaser, that releaser was termed a sign stimulus. The sign stimulus is a “signal” of some sort in the environment that triggers a certain behavior pattern.
Ethologists have found that sign stimuli always have highly predictable responses. For example, baby birds, instinctively fearing flying predators, will crouch and freeze when a shadow passes over their nest. While studying the aggressive territorial response male three-spined stickleback fish make to other males, Tinbergen discovered that the red underbelly of the male acted as a sign stimulus for other males. In fact, a red postal truck passing by the window was enough to evoke attack behavior from males in their aquarium on a windowsill. And a yawn (sign stimulus) by one person will invariably release yawning in other nearby humans.
Innate Behavior is Critical to the Survival of Many Animals
Why do most animals rely so heavily on pre-programmed behaviors such as those described? Each animal species lives in its own sensory world. It responds to a complex of signals and stimuli of which other animals, including humans, are largely unaware. Since most animals are not raised and trained by parents, they must be equipped to respond to stimuli immediately and correctly as soon as they emerge as an individual. Whether or not they are able to learn certain behaviors, doing so might take time they can ill afford to spend on the learning process. Pre-programmed behaviors triggered by sign stimuli enable animals to respond rapidly when speed may be the key to survival.
The instinctive theory of behavior as developed by Lorena and Tinbergen has been modified since their time because it cannot be shown that a behavior develops without some environmental experiences. Critics of the instinctive theory have contended that genes code for proteins and not directly for behavior so all forms of behavior depend on the interaction of the organism and environment. Given a different environment, even the most rigidly instinctive behavior patterns may be altered at least slightly.
Dennis Holley - Looking back, it's clear that I have been a science nerd my entire life. A simple, almost toy-quality microscope my poor parents scraped ...
