All animals function on innate behaviors, even in human beings. We are genetically predisposed to performed certain behaviors. It is hard-wired into our brains. The simplest form of instinct is a fixed action pattern. A fixed action pattern is a sequence of unlearned acts linked to a sign stimulus. The behavior is fixed because it is unchangeable. An instinctive stereotype sequence of behavior that once triggered usually goes to completion. The clip below showed an example of such behavior occurs in the three-spine stickleback fish. During mating season, males developed a red spot on their belly side, and this naturally triggers aggressive behavior towards other males during this time. The way male sticklebacks defend their nesting territories from other males is a fixed action pattern. During breeding season, males’ sticklebacks who have red belly build a nest and entice females who do not have a red belly to enter and lay eggs. If another male appears, it triggers the nesting male to attack. Interestingly, if an unrealistic fish model with a red underside is introduced, the same aggressive behavior is activated. If a realistic stickleback model without any red is presented, the male does not attack. Therefore, the red belly is the sign stimulus that triggers and elicit a fixed action pattern. These patterns are innate, they are not learned. In the case of sticklebacks, the hard-wired behavior helps the males pass on their genes by chasing off other males who might try to fertilize the eggs or might try to endanger their young.