ethological explanation of aggression

• fixed action patterns (FAPs)

  series or consequence of acts that occur behaviourally in animals
• Innate releasing mechanisms (IRM)

  once alerted by the sign stimulus, the IRM communicates with motor control circuits to release the FAP associated with that sign stimulus
• sign stimulus


  essential feature of a stimulus which is necessary to elicit a response
• ritualised aggression


  not all aggressive behaviour involves fighting but may be ritualised in the form of threat displays. threat displays are important for contestants because they help individuals assess their relative strength before deciding to escalate a conflict. makes dangerous physical aggression less likely to occur.
• example of ritualised aggression

  male gorillas use a variety of gestures to intimidate an opponent without the need for physical contact. threat displays are intended to make an opponent back down
• The IRM receives input from sensory recognition circuits which are stimulated by the sign stimulus. The IRM then communicates with motor control circuits to activate the FAP associated with that sign stimulus.
• Tinbergan studied stickleback fishes and demonstrated how they produced a fixed sequence of aggressive behaviours when another male stickleback fish entered its territory. 
• stickleback fishes

  The sign stimulus in this case was the red underbelly of the male stickleback and if this was covered, they were not attacked. The fact that all male stickleback engaged in this behaviour suggests it is invariant and a strong argument for the behaviour being biologically determined (nature). This behaviour is also believed to be adaptive as it increases evolutionary fitness by warding off other males from their nest while remaining inviting for female stickleback fish who do not have a red underbelly.