Nature, nurture and stages
Developmental psychologists study how we change over a lifetime. A core debate is nature versus nurture: how much comes from genes and how much from environment. Modern answer: both, and they interact. Another debate is continuity versus stages: some theories describe smooth change, others describe distinct stages.
Prenatal development
A teratogen is a substance that can harm a developing foetus, such as alcohol, certain drugs or infections. The timing and dose matter. A sensitive (critical) period is a window when experience has an unusually strong effect on development.
Piaget's cognitive stages
Jean Piaget argued children think differently from adults, moving through four stages:
- Sensorimotor (birth to about 2): learning through senses and actions. Key milestone: object permanence, knowing objects exist when out of sight.
- Preoperational (about 2 to 7): symbolic thought and pretend play, but egocentrism and difficulty with logic.
- Concrete operational (about 7 to 11): logical thinking about real objects. Children grasp conservation, such as that pouring water into a taller glass does not change the amount.
- Formal operational (about 12 on): abstract and hypothetical reasoning.
Erikson's psychosocial stages
Erik Erikson proposed a crisis at each life phase. A few: infancy, trust vs mistrust; early childhood, autonomy vs shame; school age, industry vs inferiority; adolescence, identity vs role confusion; young adulthood, intimacy vs isolation.
Attachment
Mary Ainsworth's "Strange Situation" classified infants. A securely attached infant uses the caregiver as a safe base, is upset when the caregiver leaves, and is soothed quickly on return. Insecure patterns include avoidant and anxious (ambivalent).
Moral development (Kohlberg)
- Preconventional: right and wrong depend on reward and punishment.
- Conventional: right means following rules and meeting social expectations.
- Postconventional: right is guided by abstract principles such as justice.
Parenting styles (Baumrind)
- Authoritative: warm and responsive with firm, explained limits. Linked to the best outcomes on average.
- Authoritarian: strict, demanding, little warmth.
- Permissive: warm but few limits.
- Neglectful: low warmth and low control.
Worked example
A 9-month-old watches a toy covered by a blanket and keeps looking for it. A 4-month-old might lose interest.
Reasoning: searching for a hidden toy shows object permanence, which Piaget places in the sensorimotor stage. The 9-month-old has it; younger infants do not yet. Meanwhile, a 5-year-old who insists a tall thin glass holds more juice than a short wide glass of the same amount has not reached conservation, which fits preoperational thinking.