Studies on the Origins of Human Agression

Continuous efforts have been made by researchers to provide an operational and measurable definition for human aggression. However, there is an overall agreement that aggression can be defined as ‘’any behaviour enacted with the intention to harm another person who is motivated to avoid that harm’’ (Anderson and Bushman, 2002, p28). Aggression can manifest itself in many forms such as instrumental aggression (i.e. terrorism and robbery), hostile aggression (i.e. impulsive murder and road rage) and relational aggression. There has been considerable debate surrounding the biological vs. social psychological origins of aggression, which will be explored.

Many types of theories have formulated an answer to the question of whether individuals are biologically inclined to be aggressive. Theories that explore biological origins have been put forward to argue that aggression is an innate response in humans, an example being evolutionary theories. It states that aggressive behaviour was seen as being adaptive for our ancestors for a number of reasons including deterring mates from infidelity, defending against attack and co-opting the resources of others (Buss & Shackelford, 1997). One might argue that these economic and social advantages of aggression were context-specific, as only when individuals were threatened by these adaptive problems, did they act aggressively towards others. Evolutionary theories have also emphasized that there is a gendered difference in the reproduction of aggression due to intrasexual competition (Trivers, 1972). Males have less parental investment in offspring than females, so this provides them with opportunities for greater success in reproduction. This creates greater competition among males to fight for their share of female mates, to ensure the passing on of their genes to future generations. Contemporary research has supported the innateness of aggression by exploring the cross culturalism of aggression in regards to male aggression. Theorists like Craig and Halton (2009) found that government data in the US showed men are ten times more likely than females to commit murder and Moffitt et al. (2001) found in a sample of 1000 individuals living in New Zealand, men were 2.4 times more likely to be involved in anti-social behaviour.

Despite there being clear empirical support to the claim, there are clear methodological issues. There is a lot of contradiction; evolutionary theories claim that aggression was used to protect one’s community, but in a contemporary setting, humans use aggression against their closest relatives in cases of domestic abuse and child abuse. An example is the brutal murder of a mother at the hands of her violent ex-boyfriend (The Mirror, 2017). Another example is the ‘House of Horrors’ case, where the parents of 11 children were arrested and charged with torture, child abuse, imprisonment and sexual assault (The Telegraph, 2018). This may suggest that evolutionary theories aren’t as applicable to modern society as first thought, which may be the result of changes in attitudes and social behaviour. Also, such explanations cannot account for the variability in aggressive acts or cultures. It fails to provide an explanation for the variation in aggressiveness in a number of contexts, for instance, where a woman has acted unfaithful to her husband: in one case her husband beats her, in a second her husband murders her and in the third case he gets drunk. Furthermore, it doesn’t explain cultural differences; for example, in the Yanomami culture male violence is often positively associated with a position of status, whereas in other cultures violence has negative societal associations. Thus, this questions the contribution of evolutionary theories regarding how innate aggressive behaviour is.

Another main theory that supports the biological perspective of aggression examines the role of hormones and genes. Research has suggested a positive correlation between the male hormone, testosterone, and aggressive tendencies. For example, males with high testosterone levels were more likely to be involved in delinquent and violent behaviour (Archer, 1991). Likewise, serotonin has been linked to an increase in levels of aggression in humans. More specifically, low levels of the serotonin metabolite, 5-hydroxy-indole acetic acid (5-HIAA), in cerebrospinal fluid, has been directly linked with violent behaviour. Birger et al. (2003) supported this as he discovered suicide attempters who used violent means had reduced levels of 5-HIAA in their spinal fluid.

In regards to the genetic predisposition towards aggression, twin and adoption studies have explored this. Research looked into the heritability of aggression and found that 50% of the variance in aggressive behaviour can be explained by genetic influences in both genders, whilst the other 50% can be explained by environmental factors (Rhee and Waldman, 2002). Twin studies looked at monozygotic (MZ) and dizygotic (DZ) twins and found a greater concordance rate of 87% in aggression in MZ twins, who share 100% of their genes, compared with 72% in DZ twins, who share just 50% of their genes (McGuffin and Gottesman (1985). An adoption study by Mednick et al., (1983) found a strong positive correlation between the number of criminal convictions of biological fathers and the number of criminal convictions of their sons, who had been adopted. Therefore, this supports the biological nature of aggression.

However, evidence for this theory is largely mixed. There is not yet conclusive evidence to support the theory that hormones like testosterone and serotonin cause aggressive behaviour. Some research has contradicted the relationship between testosterone and aggression; Kreuz and Rose (1972) found no significant differences in testosterone levels between prisoners who fought frequently and prisoners who did not, suggesting that testosterone does not play a main role in aggression. The issue of gender may also confound the results. Research into hormones focus predominantly on male aggression and therefore suggest that males are more aggressive than females, but this is not always the case. There are many instances where a female has committed acts of aggression i.e. murder. Rose West is an infamous serial killer who was found guilty of the torture, rape and murder of 10 young women, and sentenced to life in prison in 1995. Therefore, this criticises the biological study into aggressive behaviour.

In light of these flaws, there is the argument that aggression has social psychological origins. An explanation of these origins is the frustration-aggression hypothesis. This suggests that ‘’frustration always leads to some form of aggression’’ (Dollard et al., 1939) and referred to situations where an individual’s goals or expectations are thwarted, so they feel frustrated and often engage in aggressive behaviour. This hypothesis can be applied to a number of contexts such as sport aggression. Edmans et al. (2007) found that after players’ positions were altered in a soccer game leading to poor results, the supporters became frustrated and began throwing objects onto the field. This shows that because their expectations of the team playing well were thwarted, they became violent. Therefore, this provides supporting evidence for the frustration-aggression hypothesis.

However, this theory can be hugely criticised for being deterministic. It assumes that frustration will inevitably lead to some form of aggression but this is incorrect. In some cases, there are other factors that may cause aggression with frustration i.e. social factors like the location or the presence of weapons. Frustration can lead to a whole host of emotional responses including sadness, despair and motivation. Frustration does not only have negative effects, but can be a positive force for change as it can encourage individuals to challenge the obstacles and work harder towards their goal. Likewise, aggression doesn’t always occur out of frustration; it could be the product of revenge, social and economic instability or the lack of social consequence. Therefore, there is not a clear causal link between frustration and aggression, and devalues its contribution to the explanation of aggression.

Nevertheless, another social psychological explanation is deindividuation theory, which looks at crowd influence on an individual’s behaviour. Being part of a crowd leads to a loss of self-identity (Diener, 1980) and encourages anti-social behaviour. One might argue that this is due to individuals believing they are just another face in the crowd, so they are less likely to be identified and held accountable for their actions. Under these anonymous conditions, individuals may be more motivated to deviate from the socially accepted norms of behaviour, and instead turn to violent and aggressive behaviour. Anonymity has been found to have a direct link to group size; the larger the size of the group, the more anonymous an individual is, which leads to a greater engagement in anti-social behaviour (Kugihara, 2001). Research that explores deindividuation theory and the effect of anonymity focuses predominantly on negative social behaviour such as aggression. For instance, Silke (2003) found that perpetrators that committed around half of the violent assaults in Northern Ireland between the years 1994 to 1996 wore disguises. Similarly, Douglas and McGarty (2001) discovered that online individuals are more likely to send harmful content to others, as their identities are hidden from their victims, and thus would not face any consequences. This, therefore, provides strong support that when individuals’ identities are hidden, they are more likely to engage in anti-normative behaviour, disproving the innateness of aggression.

But, deindividuation theory has several flaws. It assumes that individuals in a deindividuated state will always act in an aggressive and violent manner, but this is not true. In some contexts, being part of a crowd can lead to an increase in pro-social behaviours. The hacktivist group, Anonymous, is an international organisation consisting of an online and offline community, so identities are protected even in public when members wear masks to conceal their identity. The group involves itself in political, social and environmental issues i.e taking down white supremacist sites, protesting against animal cruelty and hacking pro-ISIS twitter accounts. Supporters of the group have referred to them as ‘freedom fighters’, whilst others have denounced them as ‘cyber-terrorists’. Furthermore, there is a lack of supporting evidence to support deindividuation theory; for example, Postmes and Spears (1998) conducted a meta-analysis of 60 studies and found that anti-normative behaviour was not more common in large groups or crowds, contradicting the claim that group membership increases anti-social behaviour.

Alternatively, there are other models that looks at the social-environmental causes of aggression in childhood and later life. This explanation also disproves the biological nature of aggression as it states that an individual’s social environment is a central factor when explaining the causes of aggression. The ‘cycle of violence’ theory established by Wisdom (1989) states that exposure to a dysfunctional environment in childhood can lead to an increased risk of exhibiting aggressive behaviour in youth and adolescence. This was later supported by Loeber et al., (2005) who said that violent youths are twice as likely to have grown up around high rates of violence within the family. A dysfunctional environment can be categorised as childhood maltreatment or conflict.

But, theorists have tried to combine biological and social explanations of aggression. Recent studies have explored the gene vs. environment interaction, by looking at the role of the monoamine-oxidase A (MAOA) gene, and the relationship between exposure to abuse and anti-social behaviour. Fergusson et al., (2011) discovered that individuals with low levels of the MAOA gene, who were exposed to abuse in childhood, were more likely to develop anti-social behaviour in later life. Like these researchers, Anderson & Bushman (2002) developed the General Aggression Model, which integrates social, cognitive, developmental and biological explanations, in the attempt to explain aggressive behaviour. Thus, this provides us with a holistic approach that supports the innateness of aggression, but also highlights the social contexts in which aggression takes place.

To conclude, after considering the evidence, aggression can be argued to be an innate response in humans through evolutionary theories and hormonal and genetic research but there is also the argument that it is not, by looking into social psychological explanations like the frustration-aggression hypothesis and deindividuation theory. However, the flaws of each of these theories have called for an integrated approach to truly assess the role of biology in aggression. Although theorists have attempted this, an example being the genes vs. environment interaction and the General Aggression Model, there is always a need for further research to gain a better understanding of human behaviour, in this case aggression.