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 Influences in Development

• Human development is bidirectional: 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

Impact of Early Life Events

• Early experiences can significantly impact development, but experiences throughout life also play crucial roles.

• Theories such as infant determinism (the idea that early experiences are overwhelmingly influential) and childhood fragility (children are highly vulnerable to stress) have limited empirical support.

• Research shows that children are generally more resilient than previously believed.

The Nature-Nurture Debate

Genetic and Environmental Contributions

• Both nature (genetics) and nurture (environment) are essential in shaping development; it is no longer viewed as an "either-or" issue.

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

• Modern research focuses on how much each factor contributes to different aspects of development, rather than which is more important overall.

Conception & Prenatal Development

Stages Before Birth

• Prenatal refers to the period before birth.

• A zygote forms when a sperm cell fertilizes an egg, marking the beginning of human development.

• There are three main stages of prenatal development: germinal, embryonic, and fetal.

Prenatal Development

Stages of Prenatal Growth

• 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): Major organs, limbs, and facial features form.

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

Brain Development

Neural Growth in the Womb

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

• This rapid neural proliferation lays the foundation for later brain function and cognitive abilities.

Obstacles to Development

Risks During Prenatal Development

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

• Alcohol consumption can cause fetal alcohol spectrum disorder (FAS), leading to learning disabilities, growth delays, facial malformations, and behavioral disorders.

• Genetic disruptions may result from inherited disorders (e.g., Down Syndrome) or random errors in cell division.

• Prematurity (birth before 36 weeks) increases the risk of serious complications; the less time in utero, the higher the risk.

Motor Development

Development of Movement Skills

• Infants are born with automatic motor behaviors called reflexes (e.g., sucking and rooting, essential for feeding).

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

• Children learn to reach, crawl, and walk, but the rate and manner of achieving these milestones vary widely due to physical maturity, cultural, and parenting practices.

• Despite timing differences, developmental milestones are achieved in the same sequence for all children.

Adolescence

Physical and Sexual Maturation

• Adolescence is the transition from childhood to adulthood, marked by puberty (sexual maturation and reproductive potential).

• Hormonal changes involve estrogens (higher in females) and androgens (higher in males).

• Genes and environment both influence the onset of puberty.

• Primary sex characteristics: Reproductive organs and genitals.

• Secondary sex characteristics: Features not directly related to reproduction (e.g., breast development, deepening voice).

• Menarche: Onset of menstruation; spermarche: First ejaculation.

Physical Development in Adults

Changes Across Adulthood

• Most adults reach their physical peak in their early 20s (strength, coordination, cognitive speed, flexibility).

• Physical declines begin soon after, affecting muscle mass, sensory processes, and fertility.

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

Theories of Cognitive Development

How Thinking Changes Over Time

• Theories differ in three main ways:

  • Stagelike vs. gradual changes in understanding

  • Domain-general vs. domain-specific cognitive abilities

  • Principal source of learning: physical experience, social interaction, or biological development

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 (distinct stages) and domain-general (broad cognitive abilities).

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

Assimilation and Accommodation

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

• Accommodation: Modifying existing schemas to incorporate new information when assimilation no longer works.

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	Can construct mental representations, but egocentric and unable to perform mental operations
Concrete Operations	7 to 11 years	Can perform mental operations, but only for actual physical events
Formal Operations	11 years to adulthood	Can 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 hypothetical and abstract concepts.

Contributions of Piaget's Theory

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

• Children are not simply small adults; learning is active, not passive.

• Highlighted the importance of general cognitive processes across multiple domains.

Lev Vygotsky's Sociocultural Theory

Social and Cultural Influences on Learning

• 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 knowledge.

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, but 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.

• Children's social and emotional styles reflect differences in temperament (basic emotional style, largely genetic).

Temperament

Major Temperament Styles

• Early-appearing and largely genetic.

• Three major styles:

  • Easy (40%)

  • Difficult (10%)

  • Slow-to-warm-up (15%)

• About 10% of children may be behaviorally inhibited (shy, cautious).

Attachment

Emotional Bonds and Sensitive Periods

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

• Imprinting and sensitive periods are important for healthy relationships (e.g., Lorenz's geese, Rutter's Romanian orphan studies).

• Longer stays in low-quality orphanages are associated with poorer outcomes; early adoption leads to better outcomes.

Contact Comfort

Role of Physical Touch in Attachment

• Contrary to behaviorist assumptions, Harry Harlow's monkey studies showed that physical contact (not just nourishment) is crucial for attachment.

• Contact comfort: Positive emotions afforded by 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%)