The term ‘personality’ derives from the Greek word persona or mask. It refers both to an individual's attitudes and ways of thinking, feeling and behaving, and to the social ways in which individuals interact with their environment. At an individual level, personality is not a single unitary entity, but a way to organise a number of different capacities that underpin one's sense of self (Allport, 1961). At a social level, an individual personality profile allows one to be recognised over time by others, and is a powerful regulator of social relationships, which, as we are group animals, are crucial for our survival.

In evolutionary terms, personality is best understood as a regulation of biopsychosocial factors in the service of good-quality survival of the individual within the particular constraints of their habitat and environment (Box 1.1).

Theories of personality

In Ancient Greece, physicians attributed individual differences in personality to imbalances of bodily fluids or humors; other popular theories have included the influence of the stars’ positions at birth, body build and skull shape (Knutson & Heinz, 2004). In the 20th century, research into personality moved to the level of the psychological, although still influenced by dominant social assumptions such as gender or racial difference. Freud emphasised the role of innate drives, an early account of what we might now understand as the genetic basis of stress responses. He is also attributed as being the first to describe the concept of ‘defences’ against stress and their effect on the expression of adult personality. Later theorists, such as Klein and Bowlby (in somewhat different ways), emphasised the importance of the interaction between the child's innate individual features and the environment in the development of normal personality functioning.