The ethological explanation proposes that aggression can be the result of an evolved automatic biological response in the brain. It is believed that animals have a built-in neural structure (a network of neurons) which, when exposed to specific stimuli (signs or releasers) such as facial expressions, will cause the release of an automatic behavioural response (a fixed action pattern). This inbuilt biological structure or process is called the innate releasing mechanism (IRM). For example, when a dog sees a cat running away from them, they have an instinctive response to chase the cat. When the cat is still, the innate releasing mechanism is not activated; however, it is the cat running that activates the innate releasing mechanism. Consequently, the dog chasing the cat is an example of a fixed action pattern which is activated by an innate releasing mechanism. The dog’s desire to chase is automatic and instinctual in response to a cat or any other small animal running away.