Instinct

Researchers of animal behavior, ethologists, first named the stereotyped, species-typical behaviors exhibited in particular circumstances fixed action patterns, which were later called instincts. A cocoon-spinning spider ready to lay its eggs builds a silk cocoon in a particular way, first spinning a base plate, then the walls, laying its eggs within, and finally adding a lid to seal the top. The spider performs all these actions in a specific sequence, and, indeed, cannot spin its cocoon in any other way. If the spider is relocated after having spun the base plate, she will still make the walls, deposit the eggs (which promptly fall out the bottom), and spin the lid for the top. When ready to begin the next cocoon, if the spider is returned to her original base plate, she will nonetheless begin by spinning a new base plate over the first, as if it were not there.

Many fixed action patterns occur in association with a triggering stimulus, sometimes called a releaser. Baby gulls respond to the sight of their parent's bill by pecking it to obtain a tasty morsel of food. The releaser here is a bright red spot on the parent's bill; neither the shape nor the color of the adult's head have a significant influence on the response. When a female rat is sexually receptive, rubbing of her hindquarters (the releaser) results in a stereotypical posture known as lordosis, in which the front legs are flexed, lowering the torso, while the rump is raised and the tail is moved to one side (a fixed action pattern). A male rat who encounters a female in lordosis experiences another releaser and initiates copulation. Neither sequence requires any prior experience on the part of the animal.