Human development is the study of human growth and change across the lifespan, from conception to death. Human development is peculiar in the social and behavioral sciences in that its primary study is on humans as organisms that grow and develop within particular human environments. Although the academic field of human development emerged relatively recently with the advent of the child study movement in the mid to late 19th century (Siege & White, 1982), people have always been intrigued by the sometimes dramatic changes that characterize human lives. As existentialist philosophers have insightfully pointed out, we are the one species that is keenly aware of our own mortality—that one day our lives will end. This existential awareness of death in the human life cycle has been a frequent theme in Western literature, as poignantly expressed in the following famous passage from Shakespeare’s As You Like It:

William Shakespeare, 1564-1616 (the Chandos portrait

All the world’s a stage,
And all the men and women merely players:
They have their exits and their entrances;
And one man in his time plays many parts,
His acts being seven ages.
At first the infant, Mewling and puking in the nurse’s arms.
And then the whining school-boy, with his satchel
And shining morning face, creeping like snail
Unwillingly to school.
And then the lover,
Sighing like furnace, with a woeful ballad Made to his mistress’ eyebrow.
Then a soldier,
Full of strange oaths and bearded like the pard,
Jealous in honour, sudden and quick in quarrel,
Seeking the bubble reputation.

This passage also directs our attention to another important aspect of the contemporary study of human development: the attempt to identify and describe the normal predictable stages of the human life cycle. Within this investigation of normative stages of development, scholars are concerned with both change and continuity in development and how these influences interact. The most influential stage theories include Freud’s theory of psychosexual development (Renkins, 2017), Erikson’s (1994) psychosocial theory of ego development and identity formation, Piaget’s cognitive-developmental perspectives (Morra, Gobbo, & Marini, 2013), and beyond, to more modern interpretations such as Bronfenbrenner’s (1979) ecological systems.