The Hydraulic Model of Instinctive Behaviour

The way aggression is expressed is somewhat complex. After an argument, slamming the door can release pent-up anger, which is a form of aggression. The hydraulic model of aggression links together Lorenz’s theory of aggression (consisting of innate releasing mechanisms and fixed action patterns in ethology), focusing on the motivation behind an action, behaviour, and external stimuli to explain how aggression is expressed in animals.

Innate releasing mechanism in ethology

Innate releasing mechanisms (IRMs) in ethology are hardwired neural networks in the brain that recognise specific stimuli ( sign stimuli or releases ) that trigger fixed action patterns (FAPs), i.e., a sequence of actions encoded in response to these specific stimuli.

The hydraulic model of instinctual behaviour brings these ideas together to illustrate how this is implemented in an animal, considering the animal’s motivation.

Wolf mid snarl, Pixabay

Lorenz’s Hydraulic model of aggression definition

Overall, the hydraulic model visualises pent-up aggression an animal may experience and release, taking into account IRMs and FAPs and acknowledging motivation in animal behaviour.Interestingly, Lorenz’s hydraulic model of instinctual behaviour goes back to the work of Freud. He believed that aggression was an inevitable outcome because, in his view, animals, especially males, are biologically programmed to fight for what they deem necessary for their survival. These include food, territory, and the right to mate.Take a look at the diagram below:

Konrad Lorenz’s hydraulic model of motivation (1950), Wikimedia Commons

Motivation is the fluid that accumulates in the reservoir and becomes the drive to act in this mechanism.

1. Action-specific energy or pent-up aggression accumulates in the reservoir, and the sign stimulus serves as the trigger. In this case, the stimulus is the weight that clogs the reservoir.

2. A sign stimulus will ‘release’ the pent-up reservoir, resulting in FAPs, and FAPs can vary depending on how much the reservoir releases.

Once this occurs, the animal’s aggression level drops (known as behavioural quiescence) until the pent-up aggression builds back up, and the process repeats.

Motivation increases over time, so the reservoir builds up over time.

Vacuum activity and spontaneous FAPs

In Lorenz’s model, either the stimulus causes the release of the pent-up aggression, leading to FAPs, or the pressure from the reservoir spontaneously discharges.

In this vacuum activity, the pent-up aggression has built up to a point where it must be released, and it does so in the absence of external stimuli. It makes its way out and leads to a FAP.

Evaluation of Lorenz’s hydraulic model (1950)

Konrad Lorenz’s theories are essential for multiple reasons, namely through their contributions to understanding behaviour in animals, specifically aggression, and acting as a model for comparative aggression in humans.

However, the model has a few problems, which we will address here:

• It fails to acknowledge premeditated aggression: the model does not account for premediated aggression when it refers to how aggression builds up. Instead, motivation or pent-up aggression accumulates and is discharged when needed.
• It fails to consider learning: if an action has a consequence for the animal, the animal has been shown to adapt to this feedback and change FAPs during development. The model does not consider this. There is no feedback in the hydraulic model of instinctive behaviour.
• It is overly simplistic: the brain is a complex organ, and the model does not account for all the complexities involved in aggression. It oversimplifies aggression to an excessive degree, which Lorenz himself admitted. However, it is meant to be a ‘starting point’.
• There is a lack of structural evidence: the model has not been located in the brain. We still do not know where these structures are located where action-specific energy accumulates.
• Arms et al. (1979): this study measured spectators watching aggressive sports on scales of hostility. Male and female participants were exposed to stylised aggression (professional wrestling), realistic aggression, and competitive non-aggressive events. They found aggression and hostility increase rather than decrease after viewing the events. However, this was not the case for the non-competitive events. This finding suggests aggression was not released as the hydraulic model would suggest.