Maturation a genetically determined process of growth that unfolds naturally over a period of time. Arneld gesell (1928) believed course of development was largely predetermined by biological factors. John b. watson (1928, a behaviourist) placed emphasis strictly on the environment, assumed that biological factors placed no restrictions on the ways that the environment can shape the course of a child"s development. Continuous: each new event builds on earlier experiences, development is smooth. Discontinuous: a series of discrete steps or stages in which behaviours get reorganized into a qualitatively new set of behaviours. Most contemporary child researchers see development as basically continuous or quantitative, but sometimes interspersed with periods of change that are discontinuous or more qualitative. Many developmental psychologists adopt an interactionist viewpoint when it comes to individual and contextual factors, i. e. children with aggressive personality traits are more likely to join a gang or enrol in a karate class.