Growth suggests an increase in size only when the principal changes do not take place in the existing structures. For example, when the human body grows, it increases in size. In contrast, development is associated with changes in organization, which suggests specialization of cells and changes in their functioning. When human body develops, some parts start functioning in a different way. For example, as the human turns from a child into an adult, gonads start working, new contacts between brain cells form, sebaceous glands start functioning.