e of human development the science that seeks to understand how and why people change or remain in the same over time. Developmentalists study people of all ages and circumstances. empirical based on observation, experience, or experiement; not theoretical. dynamic-systems theory a view of human development as always changing. ecological-systems approach a vision of how human development should be studied, with the person considered in all the contexts and interactions that constitute a life. butterfly effect the idea that a small effect or thing can have a large impact if it happens to tip the balance, causing other changes that create a major event. computer expert in a baseball cap cohort differences become most apparent when new technology appears. socioeconomic status (SES) a person's position in society as determined by income, wealth, occupation, education, place of residence, and other factors. the culture of poverty poor nutrition, substandard housing, average life xpectancy of 52 years. ethnic group people whose ancestors were born in the same region who often share a language, culture, and religion. race a group of people who are regarded (by themselves or others) as genetically distinct from other groups on the basis of physical appearance. social construction an idea that is built more on shared perceptions than on objective reality. (ex: childhood, adolescence, yuppies, senior citizens). mirror neurons brain cells that respond to actions performed by someone else, as if the observer had done that action. replication the repetition of a scientific study, using the same procedures on a similar (but not identical) group of participants, in order to verify, refine, or dispute the original study's conclusions experiment a research method in which the researcher tries to determine the cause-and-effect relationship between two variables by manipulating one variable (called the independent