Human development refers to the pattern of growth and change that begins at conception and continues throughout the lifespan. It includes both growth and decline and can be positive or negative. There are some major principles of human development including that development proceeds from the center of the body outward and from the head downward, while the rate and outcomes of development vary between individuals. Development is a complex process influenced by biological, cognitive, and socio-emotional factors. Approaches to studying human development include the traditional perspective that sees little change after childhood and the lifespan approach that views development as ongoing throughout life in multiple dimensions.