Aggression and Its Causes: A Biopsychosocial Approach

To date, there has been little agreement on the developmental origins and semantic meaning of aggression. Pioneering social psychologist Albert Bandura (1973) quipped that reviewing the literature on aggression was like entering into a semantic jungle. Bandura (1983) defines aggression as “behaviour that results in personal injury and physical destruction” (p. 2), whereas Dollard et al (1939, as cited in Bjørkly, 2006) define it as a “sequence of behaviour, the goal-response to which is the injury of the person toward whom it is directed” (p. 9). One point of agreement across the literature is that aggression refers to intentional physical or psychological harm to another.

Previous research exploring aggression has been inconsistent and contradictory. Multiple conflicting theories have surfaced within the field of psychology differing in their views on the origin, catalysts, and regulators of aggressive behaviour (Bjørkly, 2006). Central to these disparities is their differential emphasis on environmental or individual factors in the onset and maintenance of aggression. Modern research focuses on exploring the biological, environmental, psychological, and social factors (Anderson & Bushman, 2002), in turn facilitating the understanding and management of aggression’s destructive effects on individuals, their families, and society at large. While social learning theories see human aggression primarily as a social phenomenon shaped through learning principles, this essay will argue that aggressive behaviour results from the complex interplay of biological, psychological, and social factors.

Early theorists postulated aggression as an intra-psychological phenomenon. Known interchangeably as the instinctual or dual-drive theory, Sigmund Freud postulated all aggressive behaviours are the result of an interaction between two antagonistic forces: Eros, the life instinct, and Thanatos, the death instinct (Bjørkly, 2006). Central to the dual-drive theory is sublimation, a process in which destructive energies are transmuted into more productive behavioural outcomes: if aggressive impulses are not depotentiated by the life instinct, through sublimation, then destructive aggressive behaviour will ensue. The main weakness of this theory is that the basic concepts in Freud’s theories are metaphorical, and cannot be measured using the scientific method (Tedeschi & Felson, 1994). Cognitive Neo-association Theory (CNA) differs from dual-drive theory in several important ways. Marking a shift toward cognitive psychology, CNA explains aggression as beginning with an aversive reaction to external stimuli that, in turn, create networks of internal associations that produce a negative affect that culminates in a fight or flight that results in aggressive behaviour (Anderson & Bushman, 2002). The external cues present during an aversive event become associated with the cognitive & emotional responses triggered by the event: various aggressive thoughts, emotions, and behaviours link together in memory, activating aggressive behaviours (Collins & Loftus 1975). Turning now to consider one of the most influential social theories of aggression: Social Learning Theory (SLT).

Social learning theorists maintain that aggression is evoked by the complex interplay of individual personality and social factors (Bjørkly, 2006, p. 15). Central to this view are the processes of imitation, observation, and modelling thought to be core to the development and maintenance of aggressive behaviours. First, an individual must observe aggressive behavioural events that are then encoded into memory (observation); second, these encoded memories are transformed into imitative patterns (modelling); finally, given the proper incentives, these behaviours will be performed (imitation) (Bandura, 1973). Leading on from this, Bandura claimed that family members, peer networks, and mass media are the three main sources of aggressive modelling (Bjørkly, 2006). A serious weakness of SLT is its assumption that the social world remains stable long enough for the process of learning to unfold (Stewart, 2012): modernity is characterised by the constant change in which we interact with multiple networks of disconnected communities regularly. Having provided an overview of the theory, this paper will now consider biological, psychological, and social factors implicated in the development of aggression in-depth.

There is a large volume of research accumulating discussing the impact of evolutionary processes on human aggression. Evolutionary psychologists conceptualise aggression as an evolved strategy sensitive to context (Buss & Duntley, 2006). Humans are one of the few species documented to perform coordinated aggressive massacres of their own kind (Wrangham & Peterson, 1996). Rather than a maladaptive pattern, aggression aided survival and reproduction through the forceful appropriation of resources, defending against attacks, & ascending social dominance hierarchies (Buss & Duntley, 2006). Conversely, modern social psychologists dismiss the role of evolution in aggressive behaviour (Zimbardo, 2004), viewing learning principles in combination with the influence of violent media as a primary cause of aggressive behaviours (Buss & Duntley, 2006). However, this view gives way to historical records demonstrating homicidal behaviour in humans far back into prehistory. In general, therefore, it seems that aggressive behaviour endures as one of the many environmentally-evoked responses that proved useful enough to be kept in the gene pool, resulting from a complex network of biological, psychological, and social forces.

The literature on aggression has highlighted several links between biology and aggressive behaviour. Serotonin (5-HT) is implicated in aggression more than any other molecule in the literature (Kravitz & Huber, 2003): multiple studies have linked lower levels of serotonin in the nucleus accumbens and prefrontal cortex in rats with extensive experiences of aggressive behaviour (Miczek et al., 2007). This view is supported by Linnolila et al. (1983) who found that violently aggressive individuals had a reduced response to serotonergic drugs. Neural correlates of moral reasoning identified are non-offenders were found to be impaired among populations exhibiting aggressive behaviours (Raine & Yang, 2006). This suggests that individual biological constitutions have an impact on aggressive behaviours. Interestingly, scholars have highlighted the conundrum that if offenders’ aggressive behaviours can be attributed to pathological brain functioning, then ethical issues arise as to what punishment they should be given for morally unethical acts (Miczek et al., 2007).

While multiple studies have demonstrated a link between testosterone and aggression in animals, human research has been divergent: some studies find strong positive relationships, some negative relationships, and others find no relationship (Archer, 1992). Studies in which non-human animals were castrated and subsequently injected with testosterone overwhelmingly demonstrate heightened aggressive behaviours (Book et al., 2001), and castration without subsequent testosterone administration results in decreased aggressive behaviour (Vom Saal, 1983), suggested a direct causal link between testosterone and aggression. While mechanisms through which testosterone affects aggression are still generally unknown, a general throughline is that testosterone and aggression seem to circulate around competitive endeavours such as establishing territory, mating opportunities, & competing for resources. For example, human male testosterone levels fall and remain lower when a man is married, rising after divorce (Mazur & Michalek, 1995). Rather than being a solely cognitive or social phenomenon, these observations support the hypothesis that aggression results from complex interactions of biological, psychological and social factors.

The past two decades have seen an increasing amount of literature exploring the developmental trajectory of aggression. Consistent pre-birth indicators of highly aggressive behaviour include having other young siblings, low income, & having a mother that displayed high levels of antisocial behaviour in adolescence or who started having children early (Tremblay et al., 2004). In the same vein, developmental research shows that the spontaneous onset of physical aggression in school-age children is highly unusual (Nagin & Tremblay, 1999). This indicates that developmental precursors of physical aggression are present before school age. Seeing as highly aggressive preschool children are at the greatest risk for adverse life outcomes in adulthood (Flanders et al., 2009), further research into different forms of early interventions may prove beneficial. These results reflect the evolutionary interactionist perspective, indicating that the development of aggression begins in early childhood, mediated by biological, psychological, & social factors that are not necessarily in the control of the individual themselves.

This essay set out to critically discuss theories of aggression. Aggression can be evoked and maintained through biological, psychological, and social factors such as hormonal fluctuation, neurological damage, and physical danger. These factors network in ways that may play a causal role in aggression. The data presented seem to support the hypothesis that aggression results not only from social factors, but biological and psychological factors, too. Because aggressive behaviour can be identified in early life, and these lead to violent psychosocial outcomes in adulthood, further research exploring interventions may prove useful for individuals, their families, and society at large.

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