M.H. Wahab (Islahi), BA Dip. in Psy. Counselling (NISD), PGD in Psy (UoP), PGD in CPR (UoC) MSc in Clinical and Health Psychology (R) (UoWL), Child Protection Officer of NCPA. wahab.haneefa @gmail.com

Introduction

For years, scientists have debated the influence of nature versus nurture. This controversy pertains to the scientific, cultural, and philosophical discussions about the relative contributions of nature and nurture to human culture, behavior, and personality. In this debate, “nature” refers to behaviors, traits, and dispositions that are genetically or hormonally determined, while “nurture” pertains to influences from experiences, culture, and the environment (Nature vs. Nurture Debate – GoodTherapy.org Therapy Blog, 2018).

Aggression is a widespread issue that poses significant public health risks (Rosell & Siever, 2015). Human aggressive behaviour has long been a subject of debate within the nature versus nurture framework, with arguments suggesting it is influenced by one, the other, or both. The American Psychological Association (2018) defines aggression as actions intended to cause physical or psychological harm to another person. Social psychology further defines aggression as behaviour aimed at harming someone who is motivated to avoid that harm (Bushman & Huesmann, 2010; DeWall, Anderson, & Bushman, 2012). Aggression can be categorized into two main types:

1. Hostile aggression, which is impulsive, angry, and aimed at causing harm (e.g., retaliatory or affective aggression).
2. Instrumental aggression, which is premeditated and goal-driven (e.g., to achieve money, social status, or other objectives).

According to proponents of nature, aggression is inborn and arises from within the individual. While self-control and a positive upbringing may help regulate these urges, aggressive tendencies are seen as intrinsic and persistent. In contrast, advocates of nurture argue that aggression is learned from the environment and that no one is born aggressive. However, modern perspectives have moved beyond this dichotomy to a more nuanced understanding of the complex interactions between genetics and environment (Craddock, 2011). Numerous studies highlight the roles of both nature and nurture in shaping human aggressive behaviour. This article explores how both factors contribute to the development and manifestation of aggression.

Nature and Human Aggression

The term “nature” refers to internal factors that influence behaviour. These innate traits, often present from birth, are seen as immutable and rooted in biology, including physiology, hormones, neurochemistry, and genetic makeup. This concept is often referred to as biological determinism.

Role of Brain Regions in Aggression

Two key brain regions involved in aggressive behaviour are the amygdala and the hypothalamus.

Amygdala. The amygdala, located in the brain’s medial temporal lobe, plays a critical role in processing sensory and emotionally charged stimuli. It integrates this information and communicates it to other brain regions to produce emotional, cognitive, and motor responses (Salzman & Fusi, 2010). Numerous studies have linked the amygdala to aggression. For instance, Vernet and Madsen (1970) found that stimulating the amygdala increases aggression. Neuroimaging studies using functional magnetic resonance imaging (MRI) also show that the amygdala is activated during anger or fear responses (Putman et al., 2004). Research has revealed that individuals with smaller amygdala volumes exhibit higher levels of aggression and psychopathic traits (Pardini et al., 2014). Conversely, lesions in the amygdala have been shown to reduce aggressive behaviour in male rats (Vochteloo & Koolhaas, 1987). These findings suggest that while the amygdala plays a functional role in aggression, environmental factors also influence its activation (Wang, 2022).

Hypothalamus. The hypothalamus, a small structure beneath the thalamus, is essential for regulating homeostasis and motivated behaviours. It is also part of the neural network involved in aggression. Studies suggest that specific regions within the hypothalamus either promote or inhibit aggression (Gregg & Siegel, 2001). An experimental study by Falkner and Lin (2014) demonstrated a strong connection between the hypothalamus and aggressive behaviour in cats. However, as Wang (2022) noted, further research is needed to fully understand these links.

Role of Hormones in Aggression

Hormones significantly influence aggression. Testosterone, the male sex hormone, is closely associated with increased aggression in both humans and animals. Dabbs et al. (1996) found that fraternities with higher testosterone levels exhibited more unruly behavior, while those with lower levels demonstrated more subdued behavior. Similarly, studies have shown that elevated testosterone levels correlate with violent behavior in prisoners and juvenile offenders (Banks & Dabbs, 1996). Importantly, this association is not limited to men; research indicates a positive relationship between testosterone and aggression-related behaviors in women, including competitiveness (Cashdan, 2003). However, early environmental factors, such as childhood experiences, can also impact testosterone levels, as shown by a study comparing males in Bangladesh and the UK (Wang, 2022).

Role of Neurotransmitters in Aggression

Serotonin. Low serotonin levels are linked to increased aggression. Studies have shown that violent offenders often have lower serotonin levels than nonviolent individuals (Virkkunen et al., 1987). Additionally, serotonin deficiency has been found to predict future aggressive behavior (Kruesi et al., 1992).

Monoamine Oxidase A (MAO-A). Monoamine oxidase A is an enzyme that influences aggression by regulating neurotransmitters like dopamine and serotonin. Brunner et al. (1993) discovered a rare mutation in the MAO-A gene associated with impulsive aggression in a Dutch family with a history of violent behavior. These findings highlight the role of genetic and neurochemical factors in aggression, although situational triggers also play a significant role in its expression.

Nurture and Human Behavior

“Nurture” refers to external factors that shape behaviour, including social influences, education, parenting, culture, and conditioning. Environmentalists and empiricists argue that behaviour is learned, not innate.

Role of Social Learning in Aggression

Albert Bandura’s Social Learning Theory emphasizes the role of observation and imitation in learning aggression. His experiments demonstrated that children imitate aggressive behavior modelled by adults, regardless of whether the model is nurturing or hostile. Bandura’s findings also showed that children exposed to aggressive media (e.g., cartoons or films) are more likely to exhibit aggression themselves. Boys tend to display greater physical aggression, while verbal aggression varies by gender and the model observed (Galanaki & Malafantis, 2022). These findings suggest that aggression can be both induced and reduced through environmental manipulations. However, Bandura’s study focused primarily on short-term effects and did not address long-term impacts on personality.

Role of Media in Aggression

Exposure to violent media is another environmental factor that influences aggression. Numerous studies have shown that violent video games, music, and television increase aggressive attitudes and behaviours in both the short and long term (Anderson et al., 2003; Bushman & Huesmann, 2001). For example, Addo et al. (2021) found that adverse environmental conditions amplify the effects of violent video games on aggression. However, future studies should consider additional factors, such as psychiatric history and prior exposure to violence, to better understand this relationship.

Role of Family in Aggression

Family dynamics play a crucial role in shaping aggressive behaviour. Research indicates that children from households with frequent conflicts are more likely to exhibit violence (Schudlich et al., 2004). Observing parents engage in physical aggression teaches children that such behavior is an acceptable way to handle disputes (Lin, 2023). These findings underscore the importance of family influences on the development of aggression.

Conclusion

Research suggests that both nature and nurture contribute significantly to the development of human aggressive behaviour. Biological factors, including physiology, hormones, neurochemistry, and genetic makeup, provide a foundation for aggression. At the same time, environmental influences, such as social learning, media exposure, and family dynamics, shape and amplify these tendencies. Together, these findings highlight the intricate interplay between innate predispositions and external experiences in shaping human behaviour, particularly aggression. Understanding these interactions offers valuable insights for addressing aggression and promoting healthier behavioural outcomes.