Developmental Psychology

Foundations of Development

Nature vs Nurture

The debate: How much of who we are is determined by genes vs environment?

Modern answer: It is never either/or-genes and environment interact in complex ways.

Genes influence behavior, but environment determines how genes are expressed^[1]-this is called epigenetics.

Heritability estimates tell us about populations, not individuals^[2]-even highly heritable traits can be changed by environment.

Critical and Sensitive Periods

Critical period: A specific window when an experience MUST occur for normal development.

Language acquisition has a sensitive period^[3]-learning a second language to native proficiency becomes much more difficult after the late teens.

Sensitive period: A time when the brain is especially responsive to certain experiences, but learning is still possible later.

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Cognitive Development

Piaget's Stages

Jean Piaget proposed that children think qualitatively differently at different ages:

1. Sensorimotor Stage (0-2 years)

• Learning through senses and actions
• Developing object permanence (objects exist even when hidden)
• No symbolic thought yet

Object permanence develops gradually in the first year^[4].

2. Preoperational Stage (2-7 years)

• Symbolic thinking emerges (language, pretend play)
• Egocentric thinking (difficulty taking others' perspectives)
• Lack of conservation (volume/quantity changes when shape changes)

3. Concrete Operational Stage (7-11 years)

• Logical thinking about concrete objects
• Conservation understood
• Can classify and order objects
• Still struggles with abstract hypotheticals

4. Formal Operational Stage (11+ years)

• Abstract and hypothetical thinking
• Scientific reasoning
• Can think about thinking (metacognition)

Criticisms of Piaget:

• Underestimated children's abilities
• Stages are not as distinct as proposed
• Did not account for cultural variation

When tasks are simplified, even infants show surprising competence^[5].

Vygotsky's Sociocultural Theory

Key idea: Cognitive development happens through social interaction.

Zone of Proximal Development (ZPD): The gap between what a child can do alone vs with help.

Learning happens best in the ZPD-not too easy, not too hard^ⓘ.

Scaffolding: Adults provide temporary support that is gradually withdrawn as the child becomes competent.

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Social and Emotional Development

Attachment Theory

John Bowlby proposed that infants are biologically programmed to form attachments to caregivers for survival.

Attachment Styles (Mary Ainsworth)

Measured via the "Strange Situation" procedure:

Secure attachment (~65%):

• Uses caregiver as safe base for exploration
• Distressed when caregiver leaves, comforted when they return
• Develops from consistent, responsive caregiving

Anxious-ambivalent (~10%):

• Clingy and anxious even before separation
• Not easily comforted when caregiver returns
• Associated with inconsistent caregiving

Avoidant (~20%):

• Little distress at separation
• Ignores or avoids caregiver on return
• Associated with rejecting or emotionally unavailable caregiving

Disorganized (~5%):

• Confused, contradictory behaviors
• Often associated with frightening or abusive caregiving

Early attachment patterns influence relationships throughout life^[6]-but they can change with new experiences.

Temperament

Temperament: Inborn behavioral style that appears early and remains relatively stable.

Thomas and Chess identified three types:

• Easy: Regular rhythms, positive mood, adaptable (~40%)
• Difficult: Irregular, negative mood, slow to adapt (~10%)
• Slow to warm up: Mild negativity, slow adaptation (~15%)
• Mixed: (~35%)

Goodness of fit between temperament and environment matters more than temperament alone^ⓘ.

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Adolescent Development

Physical Changes

Puberty begins earlier today than in the past^[7]-likely due to better nutrition and possibly environmental factors.

Brain development continues until mid-20s^[8]-especially the prefrontal cortex (planning, impulse control).

Identity Formation (Erikson)

Key task of adolescence: Developing a coherent sense of identity.

Identity statuses (James Marcia):

1. Identity diffusion: No exploration, no commitment

2. Foreclosure: Commitment without exploration (adopting parents' values)

3. Moratorium: Active exploration, no commitment yet

4. Identity achievement: Exploration completed, commitment made

Identity formation is ongoing-it does not end after adolescence^[9].

Social Changes

Peer relationships become central:

• Conformity to peers peaks around age 14
• Peer influence can be positive or negative
• Quality of friendships matters more than quantity

Authoritative parenting (high warmth + high expectations) is associated with best adolescent outcomes^[10].

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Adult Development

Early Adulthood (20s-40s)

Key tasks (Erikson): Intimacy vs isolation

• Establishing intimate relationships
• Career development
• Possible parenthood

The "emerging adulthood" period (18-25) has become more distinct in modern societies^[11]-delayed marriage, education, career.

Middle Adulthood (40s-60s)

Key task (Erikson): Generativity vs stagnation

• Contributing to future generations
• Career peak and reassessment
• Managing multiple responsibilities (children, aging parents)

The "midlife crisis" is largely a myth^[12]-most people do not experience dramatic upheaval.

Fluid intelligence (processing speed) declines, but crystallized intelligence (knowledge) continues to grow^[13].

Late Adulthood (60s+)

Key task (Erikson): Integrity vs despair

• Reflecting on life
• Adapting to physical changes
• Finding meaning

Emotional well-being often IMPROVES in older age^[14]-this is called the "positivity effect."

Older adults prioritize meaningful relationships over expanding social networks^ⓘ-"socioemotional selectivity theory."

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Moral Development

Kohlberg's Stages

Level 1: Preconventional Morality

• Stage 1: Avoid punishment
• Stage 2: Self-interest (what is in it for me?)

Level 2: Conventional Morality

• Stage 3: Good boy/girl (seek approval)
• Stage 4: Law and order (rules must be followed)

Level 3: Postconventional Morality

• Stage 5: Social contract (rules can be changed democratically)
• Stage 6: Universal ethical principles (conscience guides)

Criticisms:

• May reflect Western male values
• Moral reasoning does not always match moral behavior
• Carol Gilligan argued Kohlberg undervalued "care" orientation more common in women^ⓘ

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See also: [Psychology](/psychology) for cognitive biases, [Social Psychology](/social-psychology) for social influences, [Parenting](/parenting) for practical applications