Genes and environment are inextricably intertwined. Old notions of the natureānurture and braināmind dichotomy have been supplanted by a rich web of synergistic relations between nature and nurture, soma and psyche. In attempting to address the natureānurture debate, the two dominant psychological approaches of the last century ā learning theory and psychoanalysis ā agreed that experience with parents was pivotal in shaping the individualās characteristics, values and dysfunctions in adaptation. Of the two approaches, psychoanalysis continued to emphasise that biologically inherited traits limited the changes that could be effected by socialisation and environmental influences (Freud, 1920). During the last decades of the twentieth century, quantitative behavioural genetic research1 eroded classical socialisation theories that emphasised the role of parenting and early family experiences (Scarr, 1992). The role of the environment was further eclipsed by the excitement of the human genome project and the promise that molecular genetics would uncover single mutated genes that caused specific behaviours and psychiatric disorders. Instead, epigenetics revealed that the environment can lead to heritable changes in gene expression in an organism, thus focusing anew on the important role played by the social environment in the final phenotype. Furthermore, molecular genetic methods uncovered even more complex and subtle mediators and moderators of geneāenvironment interaction in the pathways from genotype to phenotype. The individualās subjective perception of the event or trauma has emerged as a potentially significant additional factor influencing the path from gene to behaviour. Thus, intrapsychic representational processes are not merely the consequences of environmental and genetic effects, but may be the critical moderators of these effects.
This chapter reviews the natureānurture debate and the advances brought by molecular genetics to the current understanding of geneāenvironment interaction. It argues for the need to integrate the findings of genetics with the insights of psychoanalytic theory, in order to enhance our understanding of the role played by the psyche, genes and environment in the impact and consequences of traumatic experiences.
Geneāenvironment interaction
The modern history of the natureānurture debate began with two cousins: Darwin, the father of the modern theory of evolution, and Galton, the father of human behavioural genetics. While Darwin (1864) investigated the genetic inheritance of characteristics,2 Galton (1869, 1883, 1889) studied the inheritance of human behaviour.3 Our understanding of human behaviour and mental life was revolutionised in the first half of the twentieth century by psychoanalysis (Kandel, 1999). Freud and his followers provided remarkable insights into unconscious mental processes, infantile sexuality and psychic determinism and about the irrationality of human motivation. Freud showed that powerful unconscious wishes motivate human behaviour and ā to the extent that these motives remain unconscious ā they determine behaviour. However, by analysing these unconscious wishes, phantasies, dreams and defence mechanisms, the individual can become more conscious of these powerful forces and no longer be subject to them, but have greater freedom of self-determination.
Although psychoanalytic thinking continued to progress in the second part of the twentieth century, there were fewer brilliant insights, with the exception of advances in the understanding of child development. Psychoanalysis still represents the most coherent and intellectually satisfying description of the mind. Its power derives from its ability to investigate mental processes from a subjective perspective, as experienced and constructed by the individual. This strength, however, is also a weakness as subjective processes do not easily lend themselves to empirical enquiry. Consequently, psychoanalysis did not progress like other areas of psychology and medicine in the latter half of the twentieth century.
Within the field of infant mental health, Anna Freud offered the first compelling evidence for the environmentās important influence in early childhood. Working in the Hampstead War Nurseries in London, her study of the traumatic effects of family disruption during the Second World War revealed
the crucial importance of early relationships between parents and children (Freud & Burlingham, 1942, 1974). Her work was extended by Spitz (1945), and later by Bowlby (1951). Their work ushered in a period of environmentalism (from the 1950s to the early 1960s). Although important genetic research was conducted during that time (Slater & Cowie, 1971), its impact on mainstream psychiatry and psychology was minor.
As behavioural and psychiatric genetics gained momentum in the 1960s, āenvironmentalismā waned (from the 1960s to the 1980s). Better twin designs and the greater availability of adoption data lead to convincing evidence for important genetic influences on most types of psychopathology. By the end of the 1980s, there was general acceptance of genetic influences on variations in the individual liability to mental disorders (Rutter et al., 1990a, 1990b, 2006). This acceptance, together with the development and application of molecular genetic strategies to psychiatric genetics, led to a decade in which environmental influences were denied (from the 1980s to the early 1990s). While quantitative genetics research determines the sum of heritable genetic influences on behaviour, it cannot identify which genes are responsible for genetic influence. Consequently, the new molecular genetic techniques initially brought great excitement and expectations that individual mutated genes would be discovered to be aetiological for specific behaviours and psychiatric disorders (Kidd, 1991). The initial claims of finding a gene āforā specific behaviours and disorders were not replicated, leading to disillusionment about the possibility of understanding the role played by genes.
Five major changes in concept occurred in the early 1990s that ushered in the current era (from the early 1990s to the present) (Rutter et al., 2006). Firstly, the simplistic notion of single basic causes was abandoned in favour of accepting that genetic effects on normal and (most) pathological development reflect the actions of many genes, each with a small effect (Lykken, 2006). Secondly, there was growing criticism of empirical behavioural genetics and extreme biological determinism. Thirdly, research strategies testing environmental mediation re-established the importance of environmental influences. Fourthly, geneāenvironment interplay received renewed interest. Fifthly, epigenetic mechanisms4 (described below) began to be elucidated. This led to the recognition that genetic effects are crucially dependent on gene expression (the functional activation of the gene) and that such expression is influenced by numerous factors including environmental features (Jaenisch & Bird, 2003).
The current understanding is that genes and environment are inextricably connected in shaping human behaviour. Numerous studies of twins, adoption and families that used quantitative genetic strategies have shown unequivocally the genetic influence on individual differences in the liability to
show particular behaviours (Plomin, 1994; McGuffin et al., 2001). Despite the shortcomings and biases of quantitative genetic methods, there is no doubt that genes substantially influence all forms of human behaviour. However, according to Rutter (2002: 996), the genetic influences are āstrong and pervasive, but rarely determinativeā.
Mounting evidence over the past two decades suggests that the social environment can moderate the expression of genetic influences on adaptive and pathological behaviour (for a review, see Reiss & Leve, 2007). The first evidence came from genetically informed twin and adoption studies that showed that psychopathology in birth parents predicts psychopathology in their adopted offspring only when the adoptive rearing environment is adverse (Cadoret & Cain, 1981). These studies do not reveal whether one or more genes are involved, nor identify the specific polymorphism (allele or form of the gene). Secondly, studies of specific alleles identified by molecular genetic techniques show that specific alleles manifest only if a child-rearing environment was adverse, or if the developing adult was exposed to stress. As in the case of genetic influences, āempirical evidence shows that environmental influences are strong and pervasive, but rarely determinativeā (Rutter, 2002: 997).
Studies of traumatic environmental effects have shown that there are large individual differences in responses: some individuals are severely affected, while others show few consequences. This has given rise to the concept of resilience: the relative resistance to the negative effects of psychosocial adversity (Luthar et al., 2000). Individual differences in response suggest that the individualās understanding and processing of the traumatic event may influence the pathway between gene and behaviour. Gabbard (quoted in Knowlton, 2005: 3) proposes that an individualās intrapsychic representational system forms an active filter between genotype and phenotype: āwhether or not environment factors trigger the expression of the gene may depend on the conscious or unconscious meaning attributed to these experiencesā. Thus, intrapsychic representational processes are not merely the consequences of environmental and genetic effects; they may be the critical moderators of these effects.
Furthermore, parents and caretakers can contextualise events to enable the child to make sense of them in beneficial ways. Anna Freud documented that a childās response to wartime air raids was largely determined by their parentās reaction to the traumatic events. Children whose parents remained relatively calm were far less traumatised than children whose parents became distressed (Freud & Burlingham, 1974). Thus, the childās subjective experience of the early environment and the quality of parenting assume ā once again ā central roles in the pathway from genotype to phenotype. Psychoanalysis re-emerges to play a potentially crucial role in explaining these subjective experiences. One implication i...
