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 instinctive behaviour in 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.
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Jetzt kostenlos anmeldenThe 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 instinctive behaviour in 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.
Fig. 1 - Aggressive displays are an adaptive response, according to Lorenz.
Lorenz stated aggression was a necessary, adaptive response in animals. By displaying aggressive behaviours, the animal in question has a higher chance of securing the means for its survival.
Lorenz believed aggression occurred due to a build-up of pressure released by a sign stimulus, resulting in specific behaviours common across the species (FAPs triggered by IRMs, as discussed above). Aggression is a means to secure survival, so it usually does not result in animals fighting to the death, interestingly enough.
It would not be productive for animals to regularly fight to the death for resources, as the species would eventually begin to suffer.
Lorenz famously stated, in how his models related to human behaviour:
I believe... present-day civilized man suffers from the insufficient discharge of his aggressive drive.²
Innate releasing mechanisms (IRMs) in ethology are hardwired neural networks in the brain that recognise specific stimuli ( sign stimuli or releases ) to 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 and aggressive displays.
A hydraulic model in psychology is a physiological or psychological model that proposes that when pressure builds in a system (i.e. a human), the built-up energy will need to be released.
The hydraulic model of aggression visualizes Lorenz's idea on how aggressive behaviours occur in animals, specifically in that aggression builds up in a reservoir over time, and a sign-stimulus or releasor unleashes the built-up aggression, resulting in aggressive behaviours. It involves a reservoir (drive), a release mechanism, a stimulus which "unplugs" the reservoir, and resulting behaviours upon release.
Overall, the hydraulic model visualises the pent-up aggression an animal may experience and how it is released, 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 (as we discussed above). Take a look at the diagram below:
Fig. 2 - Konrad Lorenz’s psychohydraulic model of motivation shows how aggression and motivation builds in animals (1950)¹.
Lorenz believed that aggression increases over time as the urge to be aggressive builds up in animals. Once the internal pressure to be aggressive builds up enough, a sign stimulus releases it, triggering aggression.
The reservoir is emptied in this case and is more sensitive the longer the time that has passed since the last release. Let's explore how the hydraulic model of instinctive behaviour links to motivation in animal behaviour, specifically, how fluid in the model builds up and drives the mechanism.
Motivation is the fluid that accumulates in the reservoir and becomes the drive to act in this mechanism.
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.
A sign stimulus will ‘release’ the pent-up reservoir, resulting in FAPs, and FAPs can vary depending on how much the reservoir releases. The spouts indicate different behaviours, and different levels of release result in different behaviours.
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. Motivation in animal behaviour is specific to the behaviours it triggers (e.g., when a species needs to mate or secure food).
A male stickleback has increased motivation to mate with a female stickleback during the mating season. This motivation rises over time and accumulates in its ‘reservoir’.
When the male stickleback encounters another male stickleback, identifiable by its red underbelly (the sign stimulus or release), it releases this reservoir. It begins its FAP, aggressive behaviour to fend off competition.
Rhoad and Kalat (1975) observed the aggressive behaviour of male Siamese fighting fish (Betta splendens) in response to other male fish (recognised by their bright colours), a mirror image of the fish, a moving model, and a stationary model. They exposed the fish to each stimulus for one hour per day.
Typically, Siamese fighting fish inflate in response to the presence of another male by inflating their dorsal, ventral, and caudal fins, among others.
Rhoad and Kalat (1975) found that the fish would puff up in response to any stimulus, exhibiting similar behaviours. The mirror image elicited a response most effectively, followed by the moving and stationary models. However, another fish is still more effective than the mirror image, and its effectiveness does not depend on the stimuli’s order.
In Lorenz’s model, either the stimulus causes the release of pent-up aggression, leading to FAPs, or the pressure from the reservoir spontaneously discharges (usually due to a lack of sign stimulus' or releasors).
Known as vacuum activities, the pent-up aggression has built up to a point where it must be released and does so in the absence of external stimuli. It makes its way out and leads to a FAP.
Typically, animals in captivity display vacuum activities as there is a lack of external stimuli to help them release pent-up aggression.
Fig. 3 - Aggression may occur spontaneously when not released, and internal pressures build up, according to Lorenz.
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:
Weakness | Description |
It fails to acknowledge premeditated aggression. | The model does not account for premeditated 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/reductionist. | 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 and where action-specific energy accumulates. |
Arms et al. (1979) measured spectators watching aggressive sports on scales of hostility. Male and female participants were exposed to stylised aggression (professional wrestling), realistic aggression (ice hockey), and competitive non-aggressive events (i.e., swimming).
They found aggression and hostility increased rather than decreased after viewing the events. However, this was not the case for the non-competitive events.
In psychology, specifically ethology, the hydraulic model is a concept Konrad Lorenz developed to demonstrate the release of pent-up aggression in animals (innate releasing mechanisms), specifically by showing a reservoir of motivation/aggression. A sign stimulus releases this reservoir to cause fixed action patterns to specific stimuli.
Konrad Lorenz proposed the psychohydraulic model (1950).
Konrad Lorenz’s theory surrounded the concept of aggression and its release in animals, explicitly referencing innate releasing mechanisms and fixed action patterns.
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.
What is the hydraulic model of instinctive behaviour?
The hydraulic model of instinctive behaviour is a concept Konrad Lorenz developed to demonstrate the release of pent-up aggression in animals (innate releasing mechanisms), specifically by showing a reservoir of motivation/aggression. A sign stimulus releases this reservoir to cause fixed action patterns to specific stimuli.
Who proposed the hydraulic model of instinctive behaviour?
Konrad Lorenz (1950).
How does the hydraulic model relate to innate releasing mechanisms and fixed action patterns?
It ties them together to show how aggression builds up and is released in an animal.
What does Lorenz’s hydraulic model derive from?
Freud’s work.
What did Konrad Lorenz believe about aggression?
He believed it was inevitable, particularly for males, as they are biologically programmed to fight for survival.
What components exist in the hydraulic model?
The components are:
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