Interactive Contributions of Genes and Early Experience to Behavioral Development: Sensitive periods and lateralized brain and behavior

Over recent years studies examining the interaction between genetic and epigenetic factors during the development of behavior have been, to a large extent, pushed aside by the focus on molecular genetics and the accompanying rise of first socio-biology and then evolutionary psychology (Bateson, 2005; Kaplan & Rogers, 2003). Despite this, some research on behavioral development has continued and now it is increasingly apparent, to neuroscientists in particular, that understanding behavior and the influence of experience is essential to expanding knowledge of brain function and development. Gottlieb's concept of "probabilistic epigenesis" is relevant to this understanding (Gottlieb, 2000, 2007; Gottlieb & Lickliter, 2007). It refers to the multiple and reciprocal influences between levels (genetic, neural, behavioral, social, etc.) on an organism's development and hence their contribution to the expression of its phenotype. In other words, his concept replaces the central dogma of molecular biology (e.g., Crick, 1970, and discussed by Lewontin, 1991), which sees causation from genes through proteins to structure and behavior as a unidirectional pathway, by a concept of bidirectionality both within and between levels. Gottlieb's conceptualization of the processes involved in development and expression of phenotype involves continual dynamic interactions between genes and environment (Gottlieb, 1998, 2000, 2002). Other authors too have drawn attention to the complex interactions between genetic and environmental influences and stressed the importance of moving away from reductionist thinking, meaning that the causation of complex behavior should not be reduced to unitary genetic explanations (e.g., Oyama, 1985; Rogers, 1999a; Rose, 1997). Despite their popularity, unitary genetic explanations of complex behavior are fallacious not only because they ignore the complex, multiple interactions between genetic expression and experience but also because they are a static view of the organism (Rose, 1997). This applies to the behavior of all species, from lower organisms to humans.