Lifespan development from prenatal through aging. Covers Piaget's stages of cognitive development (sensorimotor, preoperational, concrete operational, formal operational), Erikson's psychosocial stages, attachment theory (Bowlby, Ainsworth, secure/avoidant/anxious/disorganized), moral development (Kohlberg, Gilligan), language acquisition (critical period, LAD, stages), adolescent identity formation, adult development, and aging. Use when analyzing how cognitive, social, emotional, and moral capacities develop and change across the human lifespan.
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Lifespan development from prenatal through aging. Covers Piaget's stages of cognitive development (sensorimotor, preoperational, concrete operational, formal operational), Erikson's psychosocial stages, attachment theory (Bowlby, Ainsworth, secure/avoidant/anxious/disorganized), moral development (Kohlberg, Gilligan), language acquisition (critical period, LAD, stages), adolescent identity formation, adult development, and aging. Use when analyzing how cognitive, social, emotional, and moral capacities develop and change across the human lifespan.
Developmental psychology studies how people grow, change, and maintain stability across the lifespan -- from conception to death. The field addresses cognitive, social, emotional, moral, and physical development, asking not just what changes but why and how. The central tension is between nature (genetic endowment, maturation) and nurture (environment, experience, culture), with modern developmental science treating the interaction between them as the fundamental unit of analysis.
Piaget, Vygotsky, information processing theorists
2
Attachment
How do early bonds shape later relationships?
Bowlby, Ainsworth, Main
3
Moral development
How does moral reasoning mature?
Kohlberg, Gilligan, Turiel
4
Language development
How do children acquire language?
Chomsky, Bruner, Tomasello
5
Identity and adolescence
How does the self emerge?
Erikson, Marcia
6
Adult development and aging
What changes (and what doesn't) in adulthood?
Baltes, Schaie, Carstensen
Domain 1 -- Piaget's Stages of Cognitive Development
Jean Piaget (1896-1980) proposed that children actively construct knowledge through interaction with the world. Development proceeds through four invariant stages, each characterized by qualitatively different forms of thought. Children do not simply know less than adults -- they think differently.
Core mechanisms
Schema -- an organized pattern of thought or action. Schemas are the building blocks of knowledge.
Assimilation -- fitting new experience into existing schemas ("that four-legged animal is a dog").
Accommodation -- modifying schemas when new experience does not fit ("that four-legged animal has stripes -- I need a 'zebra' schema").
Equilibration -- the drive to balance assimilation and accommodation. Cognitive conflict (disequilibrium) motivates schema change.
The four stages
Stage 1: Sensorimotor (birth to ~2 years). The infant knows the world through action -- sucking, grasping, looking. The major achievement is object permanence: the understanding that objects continue to exist when out of sight (demonstrated by Piaget's A-not-B task). Before roughly 8 months, "out of sight" is literally "out of mind."
Stage 2: Preoperational (~2 to ~7 years). Symbolic thought emerges: language, pretend play, drawing. But thinking is egocentric (the child assumes others see the world as they do -- the three-mountains task), centrated (focusing on one dimension at a time), and lacks conservation (pouring water into a taller glass makes "more water"). Reversibility of mental operations is not yet achieved.
Stage 3: Concrete operational (~7 to ~11 years). Conservation is achieved. The child can perform mental operations (reversibility, classification, seriation) on concrete objects. Logical thinking emerges but is tied to the physical world -- hypothetical and abstract reasoning remain difficult.
Stage 4: Formal operational (~11+ years). Abstract, hypothetical, and systematic thinking becomes possible. Adolescents can reason about possibilities (not just realities), test hypotheses systematically, and think about thinking (metacognition). Not all individuals reach formal operations in all domains; cultural and educational factors play a significant role.
Critiques of Piaget
Underestimated infant abilities. Baillargeon (1987) showed object permanence understanding as early as 3.5 months using looking-time paradigms.
Stage transitions are gradual, not abrupt. Children often demonstrate abilities in one domain before another (horizontal decalage).
Cultural variation. Formal operational thinking depends heavily on schooling; it is not a universal endpoint.
Social dimension neglected. Piaget focused on the individual child constructing knowledge; Vygotsky provided the social corrective.
Domain 2 -- Attachment
Attachment theory (Bowlby, 1969) proposes that infants are biologically predisposed to form emotional bonds with caregivers, and that the quality of these early bonds shapes internal working models of relationships that persist into adulthood.
Bowlby's ethological framework
Bowlby drew on ethology (Lorenz's imprinting studies) and psychoanalysis to propose that attachment is an evolved behavioral system. The attachment system is activated by threat (separation, danger, illness) and deactivated by proximity to a responsive caregiver (the "safe haven" and "secure base" functions).
Ainsworth's Strange Situation
Mary Ainsworth (1978) developed the Strange Situation procedure to classify attachment patterns in 12-18 month olds:
Pattern
Behavior
Caregiver style
Prevalence (~US)
Secure (B)
Distressed at separation, comforted at reunion, uses caregiver as base
Sensitive, responsive
~60%
Avoidant (A)
Little distress at separation, ignores caregiver at reunion
Rejecting, emotionally unavailable
~20%
Anxious-resistant (C)
Very distressed at separation, ambivalent at reunion (seeks contact but resists)
Inconsistent responsiveness
~15%
Disorganized (D)
No coherent strategy, freezing, contradictory behaviors
Frightening or frightened caregiver
~5%
Adult attachment
Main and colleagues (1985) extended attachment classification to adults via the Adult Attachment Interview (AAI). Adults who can discuss childhood attachment experiences coherently (even if those experiences were negative) are classified as "autonomous" and tend to have securely attached children. The intergenerational transmission of attachment is one of the most robust findings in developmental psychology.
Criticisms
Cross-cultural variation in attachment distributions (van IJzendoorn & Kroonenberg, 1988) raises questions about universality of the "secure = optimal" assumption.
The temperament hypothesis (Kagan, 1984) suggests infant temperament contributes to attachment classification, not just caregiver sensitivity.
Earned security (Roisman et al., 2002) shows that adults can revise insecure working models through later relationships.
Domain 3 -- Moral Development
Kohlberg's stages
Lawrence Kohlberg (1969) proposed six stages of moral reasoning across three levels, based on responses to moral dilemmas (the Heinz dilemma):
Level 1: Preconventional (childhood). Stage 1: Obedience and punishment orientation ("it's wrong because you get punished"). Stage 2: Instrumental purpose ("I'll do it if there's something in it for me").
Level 2: Conventional (adolescence/adulthood). Stage 3: Good boy/good girl ("it's right because people will approve"). Stage 4: Law and order ("it's right because it's the law").
Level 3: Postconventional (rare in adults). Stage 5: Social contract ("laws are agreements that can be changed through democratic process"). Stage 6: Universal ethical principles ("some principles transcend law -- justice, human dignity").
Gilligan's critique
Carol Gilligan (1982) argued that Kohlberg's stages were biased toward a justice orientation (typically male) and neglected an equally valid care orientation (typically female). The care perspective emphasizes relationships, responsibility, and contextual sensitivity over abstract principles. Modern moral development research acknowledges both orientations without privileging either.
Domain theory
Turiel (1983) distinguished moral rules (harm, fairness -- universal, not authority-dependent) from social-conventional rules (dress codes, etiquette -- culturally specific, authority-dependent). Even 3-year-olds distinguish between these domains, suggesting some moral understanding is present much earlier than Kohlberg's framework implies.
Domain 4 -- Language Development
Milestones
Age
Milestone
Birth
Preference for native language, categorical perception of phonemes
~6 months
Babbling (canonical: "bababa," then variegated: "badago")
~10-12 months
First words, phonemic narrowing (lose ability to discriminate non-native contrasts)
Nativist (Chomsky): Universal Grammar is innate; children are biologically prepared for language. Evidence: poverty of the stimulus, critical period effects, universal structural principles.
Social-interactionist (Bruner, Tomasello): Language is learned through social interaction. Child-directed speech ("motherese"), joint attention, and cultural routines scaffold acquisition. Evidence: children learn language in social contexts, not from television alone.
Connectionist/usage-based: Language emerges from statistical learning over large amounts of input. Evidence: infants track transitional probabilities between syllables (Saffran et al., 1996).
Critical period
Lenneberg (1967) proposed a critical period for first language acquisition ending around puberty. Evidence from feral children (Genie, studied by Curtiss, 1977) and late-deafened individuals supports the claim that language acquisition becomes dramatically harder after the critical period closes.
Domain 5 -- Adolescent Identity
Erikson's identity crisis
Erik Erikson (1968) proposed that the central task of adolescence is identity versus role confusion -- the integration of childhood identifications, talents, and values into a coherent adult identity. Identity formation involves exploration (trying out roles, ideologies, relationships) and commitment (settling on a direction).
Marcia's identity statuses
James Marcia (1966) operationalized Erikson's theory into four identity statuses based on exploration and commitment:
Status
Exploration
Commitment
Description
Achievement
Yes
Yes
Has explored and committed
Moratorium
Yes
No
Currently exploring
Foreclosure
No
Yes
Committed without exploration (adopted parents' values)
Diffusion
No
No
Neither exploring nor committed
Identity achievement is not a one-time event. Individuals may cycle through statuses across different domains (career, religion, relationships) and across the lifespan.
Domain 6 -- Adult Development and Aging
Cognitive aging
Fluid intelligence (novel problem-solving, processing speed) declines gradually from the mid-20s. Crystallized intelligence (accumulated knowledge, vocabulary) remains stable or increases into the 60s and 70s (Schaie, 1996 -- Seattle Longitudinal Study). The brain shows compensatory activation patterns (HAROLD model -- Cabeza, 2002) and maintains plasticity throughout life.
Socioemotional selectivity theory
Carstensen (1992) proposed that as people age and perceive time as limited, they prioritize emotionally meaningful relationships over novel social contacts. This explains the "positivity effect" in older adults: preferential attention to and memory for positive information.
Successful aging
Baltes and Baltes (1990) proposed the Selection, Optimization, and Compensation (SOC) model: successful aging involves selecting domains of high priority, optimizing performance in those domains, and compensating for losses. The concert pianist Rubinstein exemplified SOC: he played fewer pieces (selection), practiced them more (optimization), and used tempo contrasts to simulate speed (compensation).
Cross-References
piaget agent: Cognitive development stages, schema theory, and constructivism. Primary agent for developmental questions.
vygotsky agent: Zone of proximal development, scaffolding, and the social/cultural dimension of development that Piaget's theory underemphasizes.
rogers agent: Humanistic perspective on self-development and self-actualization across the lifespan.
cognitive-psychology skill: The cognitive architecture (attention, memory, perception) whose development this skill traces.
social-psychology skill: Social influences on development, including conformity, group dynamics, and prejudice formation.
clinical-foundations skill: Developmental psychopathology -- how developmental trajectories go awry.
References
Ainsworth, M. D. S., Blehar, M. C., Waters, E., & Wall, S. (1978). Patterns of Attachment. Lawrence Erlbaum.
Bowlby, J. (1969). Attachment and Loss: Vol. 1. Attachment. Basic Books.
Erikson, E. H. (1968). Identity: Youth and Crisis. Norton.
Gilligan, C. (1982). In a Different Voice. Harvard University Press.
Kohlberg, L. (1969). Stage and sequence: The cognitive-developmental approach to socialization. In D. Goslin (Ed.), Handbook of Socialization Theory and Research. Rand McNally.
Piaget, J. (1952). The Origins of Intelligence in Children. International Universities Press.
Piaget, J. (1954). The Construction of Reality in the Child. Basic Books.
Schaie, K. W. (1996). Intellectual Development in Adulthood: The Seattle Longitudinal Study. Cambridge University Press.
Vygotsky, L. S. (1978). Mind in Society. Harvard University Press.
