Themes of development: origin of behavior biological vs. environmental influences, pattern of change - continuous or discontinuous development over time, contextual influences that influence developmental change. Theme 1: origin of behavior: arnold gessel. Focused on the biological factors that influence development. Concentrated on maturation (natural unfolding of an organisms genotype over the course of their life) Focused on the environmental factors that influence development. Claimed that he could produce a genius or a criminal out of anyone if given proper environment. 2 basic patterns: continuous process: (macroscopic) Each new event builds on earlier experiences. Developmental changes add to previous abilities w/o any abrupt shift. Ex: learning how to swim, you get better at it gradually: discontinous process: (microscopic) Abrupt step-like change each qualitiatively different from the one that precedes it in development. Individual characteristics can affect the context and vice versa. An aggressive child might join gangs or violent games might increase aggressive behavior in kids.