Ethological/Evolutionary Explanation for Aggression

Question 1

Adaptive functions of Aggression

Answer 1

• Ethological explanations: an explanation that tried to understand the innate behaviour of animals by studying them in natural environments.
• Aggression is adaptive to survival because the ‘defeated’ animal is rarely killed and must establish territory elsewhere.
• Benefits? Species spread out over wider and reduce competition pressure for resources.
• Also establishes dominance hierarchies.
• Male chimps use aggression to establish hierarchy.
• Pettit et al. (1988) studied groups of young children and observed aggression’s role in development of dominance over others. Children use aggressive tactics to establish dominance.
• This is adaptive (and therefore naturally selected) because dominance brings benefits (access to resources and power).

Question 2

Pettit et al. (1988)

Answer 2

Pettit et al. (1988) studied groups of young children and observed aggression’s role in development of dominance over others. Children use aggressive tactics to establish dominance.
- This is adaptive (and therefore naturally selected) because dominance brings benefits (access to resources and power).

Question 3

Ritualistic Aggression

Answer 3

• A series of behaviours carried out in a set order.
• Lorenz: most aggressive encounters consist of ritualistic signaling and rarely reached the point of becoming physical.
• Intra-species aggressive confrontations end with ritual appeasement displays.
• This is adaptive because if every aggressive encounter ended with death of one combatant, this could threaten existence of the species.

Question 4

• Innate releasing mechanism (IRM):

Answer 4

biological structure or process that is activated by an external stimulus which in turn triggers a fixed action pattern.
- Example: network of neurons (circuit), and environmental stimulus (facial expression) triggers IRM which then releases a sequence of behaviours.

Question 5

• Fixed action pattern (FAP):

Answer 5

a sequence of stereotyped pre-programmed behaviours triggered by IRM.

Question 6

• Lea (1984): FAPs have 6 main features:

Answer 6

1. Stereotyped: relatively unchanging sequences of behaviours.
2. Universal: same behaviour is found in every individual of a species.
3. Unaffected by learning: same for every individual regardless of experience.
4. ‘Ballistic’: once behaviour is triggered it follows an inevitable course and cannot be altered before it’s completed.
5. Single-purpose: behaviour only occurs in a specific situation and not in any other.
6. Response to identifiable specific sign stimulus (releaser).

Question 7

Tinbergen’s Research

Answer 7

• It is important to note that a releaser which activates the IRM will always lead to the FAP, with no further signals needed.
• This is an innate response and cannot be unlearnt, as demonstrated by Tinbergen (1951) who found that male sticklebacks will respond aggressively to model red spots, regardless of whether the model resembles a stickleback or not.
• Tinbergen had 3 models, 2 very non-fish-like and 1 fish-like. The fish-like model elicited no response due to the absence of red spots. The other 2 models elicited aggression due to the presence of red spots.
• The red spots appear during mating season and are a releaser that triggers the IRM.

Question 8

Evaluation
Research Support

Answer 8

• Support from research related to genetics and evolution.
• Brunner’s study of the MAOA gene and twin and adoption studies showed the genetic basis.
• Supports the evolutionary theory’s idea that aggression is genetically determined, heritable and adaptive.
• However,
• Cultural differences -> Nisbett found one type of homicide more common with white American men in Southern USA states than Northern USA states.
• Concluded that it was due to a ‘culture of honour’ in the southern USA states, less prevalent in the northern states.
• Suggests aggression comes from a learned social norm, not innate biological factors.

Question 9

Ritualistic Aggression

Answer 9

• There is evidence to suggest that ritualistic aggression may not be displayed by all species and in all situations.
• For example, Goodall’s (2010) observation of chimpanzees in the Gombe Stream National Park found that rival communities slaughtered each other in a systematic fashion, despite appeasament and ritualistic signals being displayed by the victims.
• This supports the idea that once a releaser has triggered the IRM, this will always lead to a FAP, and so the releaser is a stronger predictor of aggressive behaviour than appeasement.

Question 10

FAPs are not fixed

Answer 10

• However, a more accurate description of FAPs may be ‘modal’ rather than ‘fixed’.
• Hunt (1973) provided evidence that the duration of each behaviour within each FAP may vary between individuals as well as the specific other animal towards which it is targeted.
• Hence, environmental, and social factors may have significant influences on the course of the FAP, resulting in lower validity of the universal nature of FAPs as part of an explanation for aggression.
• It challenges Lorenz view that FAPs are innate and unchanging.
• Patterns of aggressive behaviour are much more flexible than Lorenz thought, especially in humans.