Human Development: How and Why We Change (Developmental Psychology)

Developmental Psychology

Overview of Developmental Psychology

• Developmental Psychology is the scientific study of how humans grow, develop, and change throughout the lifespan, from infancy to old age.

• It examines physical, cognitive, social, and moral development across different age groups: infancy, childhood, adolescence, early, middle, and late adulthood, and end of life.

• Key areas of interest include: physical development, language development, social development, cognitive development, and moral development.

Bidirectional Influences

Mutual Impact of Development and Experience

• Human development is a two-way street: children's development influences their experiences, and their experiences also influence their development.

• As individuals age, they gain more control over selecting their own environments, further shaping their developmental trajectory.

Influence of Early Experience

Resilience and Early Input

• Early experiences have a significant impact on development, but experiences throughout life also play crucial roles.

• Theories of infant determinism (early experiences are overwhelmingly influential) and childhood fragility (children are highly vulnerable to stress) are not strongly supported by research.

• Children demonstrate greater resilience than previously believed.

The Nature-Nurture Debate

Genetic and Environmental Contributions

• Both nature (genetics) and nurture (environment) are essential in shaping development.

• The debate is no longer about which is more important, but about how much each contributes to different aspects of development.

• Gene-environment interaction: The impact of genes on behavior depends on the environment in which behavior develops.

Conception & Prenatal Development

Stages Before Birth

• Prenatal refers to the period before birth.

• A zygote forms when a sperm cell fertilizes an egg.

• Three main stages of prenatal development: germinal, embryonic, and fetal stages.

Prenatal Development

Key Stages and Milestones

• During the germinal stage, the zygote divides repeatedly to form a blastocyst (a ball of identical cells).

• By the middle of the second week, cells begin to specialize, and the blastocyst becomes an embryo.

• The embryonic stage (weeks 2–8): formation of limbs, facial features, and major organs.

• By the 9th week, the fetal stage begins: major organs are established, heartbeats are detectable, and the fetus continues to mature until birth.

Brain Development

Neural Growth in the Prenatal Period

• Between day 18 and about 180 days (6 months), neurons proliferate at an extraordinary rate—up to 250,000 neurons per minute.

• Proper brain development is crucial for later cognitive and behavioral functioning.

Obstacles to Development

Risks During Prenatal Development

• Teratogens: Environmental factors that can negatively impact prenatal development (e.g., smoking, drugs, chicken pox).

• Fetal Alcohol Spectrum Disorder (FAS): Caused by alcohol consumption during pregnancy; leads to learning disabilities, growth delays, facial malformations, and behavioral disorders.

• Genetic disruptions: Disorders (e.g., Down Syndrome) or random errors in cell division can affect development.

• Prematurity: Birth before 36 weeks increases the risk of complications; less time in utero means higher risk.

Motor Development

Reflexes and Milestones

• Infants are born with automatic motor behaviors (reflexes), such as sucking and rooting, essential for feeding.

• Motor behaviors are bodily motions resulting from self-initiated force that moves bones and muscles.

• Children achieve motor milestones (e.g., reaching, walking) at different rates, influenced by physical maturity, culture, and parenting practices.

• Developmental milestones are achieved in the same sequence, though timing varies.

Adolescence

Physical and Sexual Maturation

• Adolescence is the transition from childhood to adulthood.

• Puberty: Achievement of sexual maturation, largely due to hormonal changes (estrogens and androgens).

• Emergence of primary sex characteristics (reproductive organs/genitals) and secondary sex characteristics (e.g., breast development, deepening voice).

• Menarche (first menstruation) and spermarche (first ejaculation) mark reproductive maturity.

Physical Development in Adults

Changes Across Adulthood

• Physical peak is typically reached in the early 20s (strength, coordination, cognitive speed, flexibility).

• Declines in muscle mass, sensory processes, and fertility begin soon after.

• For women, fertility declines sharply from ages 30 to 40, ending with menopause (end of menstruation and reproductive potential).

Theories of Cognitive Development

Understanding How We Learn and Think

• Theories differ in whether changes are stagelike or gradual, domain-general or domain-specific, and in the principal source of learning (physical, social, or biological).

Jean Piaget's Theory

Stage Theory of Cognitive Development

• Swiss psychologist Jean Piaget proposed the first comprehensive theory of cognitive development.

• His theory is stage-like and domain-general (applies across multiple domains of knowledge).

• He believed the endpoint of cognitive development is the ability to reason logically about hypotheticals.

Assimilation and Accommodation

• Assimilation: Absorbing new experiences into current mental schemas (models).

• Accommodation: Altering existing beliefs or schemas to make them more compatible with new experiences.

Piaget's Stages of Cognitive Development

Stage	Typical Ages	Description
Sensorimotor	Birth to 2 years	No thought beyond immediate physical experiences
Preoperational	2 to 7 years	Able to think beyond the here and now, but egocentric and unable to perform mental transformations
Concrete Operations	7 to 11 years	Able to perform mental transformations but only on concrete physical objects
Formal Operations	11 years to adulthood	Able to perform hypothetical and abstract reasoning

• Sensorimotor Stage (Birth–2 years): Focus on the present; lack object permanence and deferred imitation; major milestone is mental representation.

• Preoperational Stage (2–7 years): Can construct mental representations; limited by egocentrism and inability to perform mental operations; lack conservation (understanding that quantity remains the same despite changes in appearance).

• Concrete Operations Stage (7–11 years): Can perform mental operations on physical objects and events.

• Formal Operations Stage (11 years–adulthood): Can reason about hypotheticals, abstract concepts, and logical problems.

Contributions of Piaget's Theory

• Changed the way we think about children's cognitive development.

• Emphasized that children are not simply small adults; learning is active, not passive.

• Explored general cognitive processes that apply across domains.

Lev Vygotsky's Sociocultural Theory

Social and Cultural Influences

• Emphasized the role of social and cultural factors in cognitive development.

• Scaffolding: Parents and others structure learning environments and gradually remove support as children become more competent.

• Zone of Proximal Development: The range of tasks a child can perform with guidance but not yet independently.

Theory of Mind

Understanding Others' Thoughts and Beliefs

• The ability to reason about what other people know or believe.

• Often assessed using false belief tests, which measure whether children understand that others can hold beliefs different from their own.

Cognitive Changes in Adolescence

Brain Maturation and Risk-Taking

• The frontal lobes (responsible for impulse control and planning) do not fully mature until late adolescence or early adulthood.

• This immaturity contributes to increased risk-taking behavior, though other factors (such as more opportunities and different risk evaluations) also play a role.

• Adolescents may experience a "personal fable," believing they are unique and invulnerable.

Early Social Development

Attachment and Temperament

• Infants quickly develop interest in others; stranger anxiety peaks at 12–15 months.

• Temperament: Basic emotional style, largely genetic, evident early in life.

• Three major temperament styles: Easy (40%), Difficult (10%), Slow-to-warm-up (15%). About 10% may be behaviorally inhibited.

Attachment

Emotional Bonds and Sensitive Periods

• Attachment is the emotional connection with those to whom we feel closest.

• Imprinting (as seen in geese) and sensitive periods are important for healthy relationships.

• Studies (e.g., Rutter's research on Romanian orphans) show that longer stays in low-quality orphanages are linked to poorer outcomes, while early adoption leads to better outcomes.

Contact Comfort

• Harry Harlow's work with monkeys demonstrated that physical contact (not just nourishment) is crucial for attachment—contact comfort provides positive emotions through touch.

Attachment Styles

Patterns of Infant-Caregiver Relationships

• Attachment styles are assessed using the "Strange Situation" task.

• Four main categories:

  • Secure attachment (60%)

  • Insecure-avoidant attachment (15–20%)

  • Insecure-anxious attachment (15–20%)

  • Disorganized attachment (5–10%)