and adrenocortical reactivity and buccal cell

Background: The origins of mental disorders arise often in childhood. Early life is a period of unique sensitivity with long lasting effects on mental health. However, the mechanisms for these effects remain unclear. Objective: This thesis describes a variety of studies using a developmental framework to promote greater understanding of the influence of nature (genotypes) and nurture (e.g., environmental risk and protective factors) on outcomes later in childhood. Method: The aim of this thesis is to investigate gene and environmental influences on behavioural, emotional, and cognitive outcomes in different samples from the Netherlands and Singapore, most derived from the general population. We assessed early life influences from a neurobiological, social, and a psychological perspective by using a biopsychosocial framework. Results: Our studies support the hypothesis that all experiences during life, including early experiences in utero, will influence the expression of genes and in the end the mental health of individuals. However, genotypes influencing stress responses are found to be ‘‘plastic,’ ’ which implies that they can be modulated by environmental experiences during life. In line with this, patterns of resilience are found to be context-dependent too. Conclusions: The model of ‘‘epigenetic programming’ ’ suggests the predictive power of the environment in utero and early childhood on mental health later in life. This association is probably determined by a neurodevelopmental pathway with individual differences in neural and endocrine responses to stress.

Developmental psychologists have identified a discrete group of children who, despite similar biological or behavioral sus-ceptibilities, either wither or bloom depending on the environ-ments in which they are reared. The differential-susceptibility hypothesis (Belsky, Bakermans-Kranenburg, & van IJzendoorn, 2007) and the related theory of biological sensitivity to context (Boyce & Ellis, 2005) contend that within the right rearing environments, individuals with traits that make them suscep-tible to environmental influences will achieve levels of adap-tation that regularly exceed those of their less susceptible, presumably hardier peers (Ellis, Boyce, Belsky, Bakermans-Kranenburg, & van Ijzendoorn, 2011). However, if susceptible individuals are born into environments that afford constant diets of adversity, their susceptibilities will function princi-pally as vulnerabilities that predispose them to many of the