animal aggression is a subject that has intrigued humans since its beginnings. Violence, generated by aggression, is found in various situations of the natural world, from social behaviors to the prey-predator relationship , and even in the care of offspring. An example of this is the hen, which if made deaf, attacks anything that passes by including its chicks, because they are seen as potential intruders. Aggression in this form translates as an extreme form of protection , which sees the hen as a protector, the chicks as something to be protected and everything else as potential predators.
This aggressive attitude is driven by whole factors linked to the stressor sphere, which is however modulated by various environmental factors. Let’s think of a beautiful Thomson’s gazelle ( Eudorcas thomsonii ) in the savannah. The gazelle sees a lion who would like to take her. The gazelle, seeing that it is in the wild and has a large space, decides to flee and try its luck. The situation is different if we consider a stray dog that runs away from humans. If this dog is cornered and has no possible escape route, lower your ears and start growling. These two different (though not so much) situations can be described through the fight or flight mechanism (W. Cannon, 1932), or fight or flight .
This reaction, managed by cascade biological systems involving the sympathetic and parasympathetic nervous systems, is modulated by cognitive and environmental factors . In our examples, both animals wanted to escape from the situation, but while the gazelle had the chance, the dog was forced to remain still and the internal motivational pressure generated the fear-driven aggressive behavior (also visible from lowered ears).
Fig. 1: fight or flight mechanism between cats
What advantage would one of these animals gain in destroying the other? Neither of them interferes in the vital interests of the other!
- Lorenz, “Aggressiveness“
Lorenz’s psycho-hydraulic model of animal aggression
According to the Nobel Prize winner Konrad Lorenz, animal aggression was guided by a motivational model , that is, we should consider the weight that different emotional spheres have on a possible instinctive aggressive response.
Fig2. Lorenz psychohydraulic model
In Fig. 2 we can see that there is a weight (P) which corresponds to external stimuli. The reservoir (S) is the vessel for internal impulses, which is filled by the tap or “nervous system” (R). The pressure inside the tank generates an impulse pressure , contrasted by a spring valve (V and M), a sort of block of instincts . The heavier the weight, the looser the block becomes, and more and more fluid flows out. In the model, the escaping liquid reaches a dispenser Vg, which corresponds to different degrees of action.
Lorenz defines aggression as a dispersive and asocial force , rooted in a real innate instinct towards aggression. According to him, there are two types of aggressive behaviors, those intraspecific and those interspecific . Only the intraspecific ones should be considered as real aggressors, because they would be linked to “doing harm”, an action unrelated to simple survival.
The most ecological view of aggression
Over the years, the study of “true” aggression, that is, the actions we consider violent, which are intended to cause pain or to be a deterrent, has turned its gaze to a more ecological approach. Aggressive behavior is seen as a plastic action, driven by the presence / absence of resources. According to Wilson (1979), the flexibility of aggression directly depends on the conquest of natural resources, which generates strong forms of competition . Resources can be sexual partners, food, water, and burrows.
A competition is formed when the goals of two or more individuals are incompatible, or when they cannot have the same resource. There are two main types of competition:
- Scramble Competition : resources are widely dispersed and cannot be monopolized. In this situation competition is generated, but aggressive behaviors such as direct aggression are more rare or less frequent;
- Contest Competition : resources are concentrated in specific places and can be easily monopolized. In this case, the strongest or most experienced animals can control them through deception and physical coercion. Dominance hierarchies develop precisely in this context.
If we consider the relationship between costs and benefits of a possible aggression, of particular interest is the ” The Imbalance of Power Hypothesis “, or hypothesis of the imbalance of power, studied in chimpanzees ( Pan troglodytes ). The principles of this hypothesis are based on the coalitions that occur within a group, and increase the status of dominance and power. In this case the coalitionary killing of other smaller groups would have a relatively low cost!
Read also: Going to counterattack: mobbing in ethology
Conclusion
We have seen that animal aggression is a very broad topic that embraces many contexts: psychological, behavioral, social and cognitive. Lack of resources and their monopolization generate individual pressures that drive an aggressive response. At the same time, in social species there is not only flight and aggression, but also tolerance . Tolerance indicates that the individual is aware of the possible repercussions of an aggressive action, and therefore seeks to mitigate, through certain reconciliation and subordination behaviors, the arousal caused by the situation.