One evolutionary explanation of group displays of aggression believes that humans display aggression in groups in order to gain access to resources; likely resources gained through group displays of aggression include land, women and money. The acquisition of these resources is important for the survival of a group and to ensure the continued existence of future generations in terms of reproduction. This explanation also argues that group displays of aggression towards potential threats are one of the best ways in which to secure the resources which are much desired by groups. Aggression as a group of humans on an individual in another territory is a low-risk strategy in order to gain more resources, more food, more females and more offspring, thereby passing more genes onto the next generation (in line with Darwinian evolution).

Group displays of aggression may occur due to xenophobia - also known as the threat of the unknown. It is evolutionarily advantageous to be wary of something unknown and to display aggression when faced with something which could potentially be a threat to our survival and/or reproduction. Aggression displayed as a direct result of xenophobia would ensure that the group is protected and would send a signal to other potentially threatening out-groups that the in-group is prepared to defend itself. Again, this would have the direct benefit of increasing the chance of survival and future reproduction of all members of the group.

Displays of group aggression can be seen in sporting events. The evolutionary explanation would argue that xenophobia plays a large part in aggression displayed by sporting groups as they are scared of the unknown opposition which poses a threat to them. Evolutionary explanations of group displays of aggression can also account for ritualised aggression observed in modern society; ritualised aggression in sports such as rugby has the benefits of success without the dangers. Victory in sport can bring status to players and winners may be seen as more desirable to women, therefore increasing players’ chances of finding a mate. Sporting events can also be territorial, especially amongst fans.

Group aggression is also seen in warfare, whereby one group attacks another in order to gain the resources they possess. This would have the evolutionary benefits of the expansion of one’s own in-group, the acquisition of desired resources and the opportunity to become a larger and more powerful group which is less likely to be attacked by the opposition. All of these benefits would greatly increase the survival opportunities of the in-group, proving aggression to be a valuable and necessary behaviour to display.

The evolutionary explanation of group display of aggression is supported by research into both sporting events and warfare. Foldesi (1996) conducted research into forty football matches which occurred between both Club sides and National sides. The researcher found that there were a greater number of violent incidents and aggressive behaviours reported when National side matches were played. The evolutionary explanation would argue that this behaviour is a direct result of the xenophobia experienced by coming into contact with the opposing team. This was seen more when the opposing team involved Gypsy, Jewish or Russian individuals and may have been because contact with Gypsy, Jewish and/or Russian members of society occurs less often in the lives of the football supporters, thus producing a perceived threat to their survival which would not otherwise occur.

Support for the evolutionary explanation of group displays of aggression can also be seen in studies which have looked at warfare. Chignon (1975) conducted a longitudinal study of the Yanomamo tribe who have a long history of war with other tribes. He found that the married male members of the tribe were far more likely to have been to war and have killed members of the opposing tribe, suggesting that displays of aggression are perceived as an attractive behaviour in a mate. Through studying the tribe, he discovered that war had many benefits such as the acquisition of land and of women who could then be used to expand the members of the existing tribe. Chignon’s findings could be explained by the evolutionary explanation as beneficial in terms of the survival and reproduction of its members. Males who survived war were considered more attractive by women and were more likely to be able to reproduce with women from both their tribe and the recently conquered tribe. The winning tribe would also have access to additional land in which to expand, allowing the members to use its resources in order to support and provide for additional generations.

Both Foldesi (1996) and Chignon’s (1975) studies help to add support for the evolutionary theory of group displays of aggression as they identify how the evolution and maintenance of aggressive displays has helped to maintain the survival and success of the groups in question. This in turn, strengthens the theory and its application to a number of different settings, giving the theory external validity.

Despite much supporting evidence, research into the evolutionary explanation of group display should not be considered conclusive as there is much research which questions the validity of the explanation. After studying incidences of group aggression in sporting events, Marsh claimed that aggression could be viewed as an alternative career structure for working class males. Aggression displayed by such males is arguably therefore not based on xenophobia but is instead a form of ritualised aggression which serves little evolutionary purpose in terms of reproduction and survival, other than as a potential career pathway. However, it could be argued that any behaviour which increases a human’s chance of ‘success’ could be evolutionary advantageous as a better career would provide more money and resources, therefore making a male more attractive to potential female mates.

The evolutionary explanation of group displays of aggression can also be criticised as it fails to take into account other factors which may be a cause of the group displays of aggression. Social psychological influences would help to explain how and why group aggression occurs through a psychological rather than evolutionary manner, yet are ignored. It is perfectly plausible that group displays of aggression are a result of the observation and imitation of such behaviours from a role model or as a result of deindividuation which is brought on by being in a large group. Deindividuation theory is a logical explanation for group displays of aggression as it states that individuals in a large group are less likely to be identified and therefore more likely to behave in ways which they would not ordinarily, e.g. aggressively. Neither social learning theory nor deindividuation theories are taken into account within the evolutionary theory and this thus weakens the theory’s overall application and effectiveness.

In addition to the criticisms identified above, determinism is a key criticism of the evolutionary explanation of group displays of aggression as it takes the view that humans have evolved to behave in aggressive ways and that this will be seen in all groups; it assumes human group displays of aggression are determined by our need to survive, gain resources and reproduce. Underestimating the role of free-will in aggressive behaviour and taking the viewpoint that aggressive behaviour is ‘necessary’ could be considered irresponsible as evolutionary explanations potentially exonerate anyone who considers it acceptable to behave in an aggressive manner in a group.
The fact that displays of aggression do not occur in all groups (e.g. religious groups), reduces the overall validity of the explanation. This explanation could be considered ethnocentric as group explanations of human aggression focus on Western industrialised views of aggression and may not account for cultural differences in collectivist countries. For example, Cassidy et al (2007) investigated Mela (a large Hindu festival) with 50 million people. Crowds behaved well and showed increased pro-social behaviour; showing crowd behaviour and collective living promote non-aggressive behaviour. Groups of humans are not always aggressive: crowds do not always lead to aggression as evolutionary explanations state which limits the validity of this explanation.
The evolutionary explanation can also be criticised for being a post-hoc explanation, thus making it difficult to test empirically. This is because we cannot be sure that we have evolved to display aggressive behaviours in order to gain resources and as it is impossible to retrospectively and scientifically test this explanation, we will never be able to completely verify its accuracy. The reduced validity and reliability of the explanation makes it likely that more than just evolutionary factors are responsible for the human aggression we see in groups today and therefore more than just the one explanation should be considered when attempting to explain group displays of aggression.