Life is a series of changes. Beginning as tiny,
two-celled organisms, people eventually become babies, children, teenagers, and adults.
Countless new skills, both simple and complicated, accompany each new stage. Babies
learn how to smile and laugh, children learn how to count and spell, and college
students learn how to set their own schedules and wash their own clothes.
All the changes that mark our lives make
up a process called development, which is the series of age-related changes that
happen over the course of a life span. Many factors influence development, including
genes, parental upbringing, parents’ educational and economic backgrounds, and life
experiences. Even historical events over which we have no control can
influence our development.
