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 first language after age ~7 becomes much more difficult.
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 typically develops around 8 months[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Scaffolding: Adults provide temporary support that is gradually withdrawn as the child becomes competent.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[7]-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[9]-likely due to better nutrition and possibly environmental factors.
Brain development continues until mid-20s[10]-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[11].
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[12].
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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[13]-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[14]-most people do not experience dramatic upheaval.
Fluid intelligence (processing speed) declines, but crystallized intelligence (knowledge) continues to grow[15].
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[16]-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
References
- Ian C. G. Weaver et al. (2011). Broad Epigenetic Signature of Maternal Care in the Brain of Adult Rats. PLOS ONE. [DOI]
- Stephen J. Bezek et al. (2020). Estimating the heritability of psychological measures in the Human Connectome Project. PLOS ONE. [DOI]
- Joshua K. Hartshorne, Joshua B. Tenenbaum, Steven Pinker (2013). The Critical Period Hypothesis in Second Language Acquisition: A Statistical Critique. PLOS ONE. [DOI]
- Katherine E. White, Jozsef Fiser (2020). Pupillometric VoE paradigm reveals 18-month-olds spontaneously represent occluded objects. PLOS ONE. [DOI]
- Fabian Stapel, Christine Hunnius, Sabine Bekkering, Harold (2013). Looking Ahead: Anticipatory Gaze and Motor Ability in Infancy. PLOS ONE. [DOI]
- Maria Morelli et al. (2022). Parental bonding in retrospect and adult attachment style: A cross-cultural study. PLOS ONE. [DOI]
- Lise Aksglaede et al. (2008). Forty Years Trends in Timing of Pubertal Growth Spurt in 157,000 Danish School Children. PLOS ONE. [DOI]
- Beatriz Luna et al. (2011). Cognitive Control in Adolescence: Neural Underpinnings and Relation to Self-Report Behaviors. PLOS ONE. [DOI]
- Aileen S. Garcia et al. (2023). The sum of all parts: Racial and ethnic identity formation during emerging adulthood. PLOS ONE. [DOI]
- Sabrina Robijahs et al. (2022). Authoritative parenting stimulates academic achievement via self-efficacy and intention. PLOS ONE. [DOI]
- Florencia Pezzutto et al. (2019). Effects of mother-offspring and father-offspring dynamics on emerging adults' adjustment. PLOS ONE. [DOI]
- Caroline Kraus et al. (2015). Unequally Distributed Psychological Assets: Social Disparities in Optimism and Life Satisfaction. PLOS ONE. [DOI]
- Douglas M. Tucker-Drob (2019). Age and cognitive decline in the UK Biobank. PLOS ONE. [DOI]
- Germaine Y. Cheng et al. (2018). Positive perception of aging is a key predictor of quality-of-life in aging people. PLOS ONE. [DOI]