3.4 Nature and Nurture

3.4 Nature and Nurture

For evolutionary developmental biology and psychology, the developing individual and most of the associated traits emerge from an interaction between nature (genetically based programs that guide development) and nurture (experiences that influence how and when these programs are expressed). As described by Sandra Scarr and Kathleen McCartney, the relative contributions of heritable and environmental effects on children can vary from infancy through adolescence. During infancy, the environments children experience are largely controlled by their parents and thus nurture should outweigh nature. As children grow, the influence of parents begins to decline and heritable influences are more strongly expressed. These influences are expressed as children seek their own experiences and build their own niches in their peer groups and in the wider world. In other words, nature influences, to some extent, how children react to other people, how other people react to them, and how interested they are in learning about the biological and physical world, among other traits.

The result is that many estimates of heritable influences on developing traits become larger as people develop into adolescence and adulthood. However, it is not yet fully understood how the expression of heritable influences is influenced by evolutionarily expectant experiences. As described by William Greenough, James Black, and Christopher Wallace, evolution has resulted in a linking of brain development and the expected experiences that will ensure that brain, cognitive, and social development is normal for the species. As an example, human language emerges naturally, that is, without instruction, and is dependent on the maturation and functioning of an integrated system of brain regions. Though heavily dependent on nature, language will not be normal unless the child is exposed to language and social discourse: The natural language systems need experience to develop normally. Variation in language competencies may be partly heritable, but the expression of these heritable differences may also be related to differences in the types of experiences children seek as these competencies emerge.