It was hypothesized by John Locke, that an individual begins life as a tabula rasa or ‘blank slate’. Locke presented in 1690, Essay Concerning Human Understanding, which argued an originary state of formlessness (R. Duschinsky), whereby the mind is receptive to learning, but experience is the determinant in attaining knowledge. Locke’s behaviourist perspective favours the role of experiential growth (nurture), over genetic predisposition (nature), in the development of human behaviour. This notion is inaccurate, as in actuality, the shaping of human behaviour does not rely solely on learned experience. Human behaviour is in fact a mutual interaction of both genetic and environmental factors, with genetic predisposition playing a substantial role. It was argued by G.W Leibniz that an individual inherently contains the sources of various notions which external objects merely rouse up on suitable occasions. This essay will concur with Leibniz’s philosophy that in fact it is the interplay of individual nature and nurture which drives the development of human behaviour, in particular, antisocial behaviour, to in turn, contradict John Locke’s tabula rasa hypothesis. Antisocial behaviours are disruptive acts characterised by hostility, intentional aggression towards others and destructive behaviour. The behaviour includes repeated violations and definance of social rules and authority, and a reckless disregard for self and others. It is characterised by deceitfulness and theft, and is considered socially unacceptable (D.C Hardy). Researchers have produced convincing evidence that antisocial behaviour in adulthood is often the product of childhood/adolescent conduct problems. Patterns of persistent deviant behaviour, attention difficulties and overly aggressive behaviour (Moffitt, 1993, 2003) are associated with antisocial behaviour later in life. Between forty to fifty percent of children who manifest these developmental precursors (Lytton, 1990) displayed Antisocial Personality Disorder (APD) in adulthood. Research from behavioural genetic procedures including twin and adoption heritability studies, have been utilized as a means of revealing the influence of genotype relative to the environment. A considerable body of evidence supports the idea that certain traits, including behavioural traits, have a substantial heritable component (burton). Longitudinal studies conducted comparing twins reared in shared versus non-shared environments, investigated the significance of both genetic factors and environmental pressures in the development of personality and behaviour (Rhee & Waldman, 2002 ; Jacobson et al. 2002 ; Tuvblad et al. 2006). This methodology relied on the different levels of genetic relatedness between monozygotic ‘identical’ (MZ) and dizygotic ‘fraternal’ (DZ) twins, to determine the contributions to individual differences in a specific phenotype. As MZ twins share one hundred percent identical genetic material, and DZ twins share, on average fifty percent of their genes, any variations between the expression of a phenotype can be attributed to experiential factors. A Minnesota study (Tellegen et al., 1988) examined 217 monozygotic (MZ) and 114 dizygotic (DZ) adult twin pairs who had been reared together in the same environment and 44 MZ and 27 DZ adult twin pairs who had been reared apart in differing environments. The study measured a number of different traits including wellbeing, aggression, achievement, and traditionalism. The results showed a substantially higher correlation across all personality attributes in MZ twins reared together than in DZ twins reared together. Almost identical results were found for twins who were reared apart and had been separated for many years. Given the identical twins were raised in completely different family environments, the expection would be that the correlation between personality traits would be much lower. The fact that these results were almost identical provides strong evidence that traits are in deed, inheritable.

Similarly, a series of studies of Swedish adoptees have demonstrated the role of nature and nurture in behavioural development (Cadoret et al. 1995). It was determined that an adult adoptee, whose biological parent a had tendency for antisocial behaviour, is three times more susceptible to have issues with antisocial/aggressive behaviour, than a person who does not. Also, a person whose adoptive parent had APD, is three times more likely to display antisocial behaviour, regardless of their biological history (burton). This research demonstrates the influence biological predisposition has on individual characteristics and demonstrates that human cognition is not shaped solely by environmental factors, but more relying on biological instinct. The evidence from both twin and adoptees studies is undeniable; hereditary factors do in fact make a sizable contribution to differences in personality and behaviour and therefore demonstrates the inaccuracies in Locke’s tabula rasa hypothesis.

With regards to specific genes, understanding of the human genome and the influences it has on human behaviour remains preliminary. However, research on specific genes in human populations have begun to provide evidence for the contribution of genes in the development of APB. It is important to recognise that single genes do not appear, to deterministically cause APD, but rather interact with each other. It is more likely that numerous genes are either directly or indirectly involved and have yet to be identified. On the genetical level, the gene most strongly associated with antisocial behaviour, is the gene responsible for producing the enzyme monoamine oxidae (MAOA), and is located on the X chromosome. The enzyme MAOA breaks down the neurotransmitters dopamine, serotonin and norepinphrine. Although a low-MAOA genotype does not, on its own, cause APD, it appears that its presence places an individual at risk of developing APD, as deficiencies in the MAOA gene have been related with aggression. If the right environmental triggers are present such as physical or sexual abuse, or a violence family environment APD can result. This research contradicts Locke’s position on the importance of nurture, when in fact, genes can predispose an individual to specific behaviour, including antisocial behaviour.

Understanding the development of human behaviour from an evolutionary perspective enables an understanding an of the causal processes that lead to the development of APD. It is a likely process of genetic selection due to specific environmental pressures, whereby aggressive behaviour is an adaptation to environmental pressures which provides a selective advantage. Buss and Shackelford (1997) provide an outstanding explanation of the underlying premises of an evolutionary perspective towards aggressive behavior. It was argued that aggression can be viewed as an adaptive response to external stimuli. The way in which genes and the environment interact renders the individual more flexible in dealing with environmental threats. This relates to the nurture position in that, an individual with a genetic predisposition to antisocial behaviour

Research has demonstrated that the development of human behaviour spans beyond the influence of individual experience, to a cognitive and biological level of functioning. Neuroimaging studies have been used to document that deficits and lesions in portions of the brain (ie. frontal lobes of the cortex), related to executive functioning, have been demonstrated to predict overly aggressive, impulsive, antisocial behaviour. A recent study conducted at Vanderbilt University, found a link between ‘an overly reactive nucleus accumbens’ and antisocial behaviour. In this study, a correlation between a robust dopamine release and a high rate of impulsive antisociality was established, providing evidence of the relationship between an individual’s innate ‘reward system’ and an individual’s behaviour. The study concluded that a responsive ‘reward system’ may pose an indication of antisocial behaviour.

A series of studies conducted in Amsterdam, the Netherlands, investigated the relationship between neuroendocrinological systems and human behaviour, in delinquent adolescent males. The study examined the activity of the hypo-thalamus-pituitary-adrenal (HPA) axis (stress regulating system), and its relationship with antisocial behaviour. With respect to the study of antisocial behaviour, the HPA activity has predominately been investigated within the templar of the low arousal theory. This theory suggests patterns of low arousal to be characteristic of antisocial behaviour. This can be interpreted with the fearlessness theory, with claims that low arousal levels are indicative of low levels of fear (Lykken, 1957; Raine, 1993), resulting in an inclination to partake in delinquent acts and antisocial behaviour. Without a normal level of biological stress regulation, there is a lack of fear conditioning. This low level of arousal at baseline in response to violent or typically anxiety-provoking stimuli can also be observed through the psychological analysis of psychopaths. The amygdalae of a psychopath has been shown to be less active during aversive conditioning, expression recognition and emotional testing. This is indicative of psychopathy and heightens the risk of the individual developing antisocial behaviour.

Similarly, an interaction between cortisol and testosterone was found to result in overt aggression. However, the relationship between testosterone and aggression was only present with low levels of cortisol, not with high levels. These results indicate that cortisol acts as a moderator between testosterone and overt aggression in males (Popma et al., 2007b).

It is obvious that both genetic predisposition and experiential growth are essential components of the human condition. It therefore than can be concluded that in fact human behaviour is influenced by an interplay of environmental factors and genetics, but it is genetic predisposition which provides the fertile ground for the development of human behaviour, in particular antisocial behaviour. John Locke’s tabula rasa hypothesis should therefore be regarded as a mere rhetoric extreme of human originary potentiality.