Tinbergen emphasized the importance of both instinctive and learned behaviour to survival and used animal behaviour as a basis for speculations about the nature of human violence and aggression.
This species of fish is very territorial and aggressive. In the mating season they develop a red spot on their underside. Tinbergen observed that at this time male sticklebacks will attack another male stickleback that enters their territory.
The following reenactment, at Fukui Japan, shows how the stickleback does not attack the fish without any red marks, but how it immediately attacks those with red undersides, regardless of the apparent size of the opponent: