Temperament
The biologically based emotional and behavioral style present from infancy.
What it means
Temperament is the set of early-appearing, biologically rooted individual differences in emotional reactivity, activity level, attention, and self-regulation that form the foundation on which later personality develops. Identifiable in infancy and partly heritable, temperament dimensions — such as negative affectivity, surgency/extraversion, and effortful control in Rothbart's model, or classic categories like 'easy,' 'difficult,' and 'slow-to-warm-up' — show meaningful continuity into adult traits like the Big Five. Temperament is shaped by, and interacts with, the environment over development rather than being fixed destiny. It matters because it represents the earliest measurable layer of individual differences in decision-relevant tendencies — reactivity, approach/avoidance, and self-control — and clarifies how much of adult personality is grounded in early biology versus experience.
Examples
An infant who is highly reactive and slow to soothe often grows into a more cautious, anxiety-prone adult.
Two siblings raised in the same house differ from the first weeks: one settles happily into any new room, the other cries at every stranger, long before parenting could explain it.
A four-year-old who waits her turn and stays with a hard puzzle is showing effortful control — the same regulation her teachers will later be calling conscientiousness.
First described in Thomas & Chess (1977); Rothbart; Kagan.