Development
PS 101: General Psychology
Development - Fall 2025
Development Question #1: Heredity vs. The Environment
Nature Argument: Genetics and biology determine who we are.
Nurture Argument: We are born as a tabula rasa (blank slate), shaped entirely by environment and socialization.
Heredity vs. Environment: An Interaction?
Interaction Argument:
Neither nature nor nurture can consistently explain development on their own; behavioral traits arise from their interaction.
The Environment Alters Our Gene Expression
Epigenetics:
The study of how environmental factors influence gene expression.
Maturation:
The orderly development of behavior patterns based on genetic “blueprints.”
Development Question #2: Continuous vs. Stage Development
Continuity: New behaviors build upon previous developments.
Discontinuity: New behaviors differ in quality from preceding stages.
Psychologists who emphasize learning view development as continuous, while those focused on maturation view it in stages.
Development Question #3: Critical Periods in Development
Concerns about the importance of timing in environmental input for learning skills.
Critical Periods: Windows in development where specific experiences are essential for the development of certain behaviors.
Imprinting:
Newly hatched ducklings follow the first moving object they see as a protective attachment.
Critical Periods & Harlow’s Monkeys
Harry Harlow's 1950’s study:
Baby monkeys deprived of maternal contact comfort exhibited:
Inappropriate aggression
Excessive timidity
Maladaptive repetitive behaviors
Such behaviors persisted into adulthood.
Can Childhood Imperfections Lead to Lifelong Deficits?
Early attachment and social adjustment in the first six months of life may be crucial, but children can recover with later nurturing experiences.
Example: Infants raised in impoverished orphanage conditions can develop well-adjusted personalities if later provided loving care.
Experimental Designs for Studying Development
Cross-Sectional Studies: Compare multiple cohorts at one time.
Risk of cohort effect due to generational differences.
Longitudinal Studies: Follow the same cohort over time, more costly and time-consuming.
Risk of loss to follow-up.
Cross-Sequential Studies: Combine cross-sectional and longitudinal methods, following multiple groups over shorter periods.
How Can We Study Child Development?
Infants cannot verbally express thoughts, making developmental study challenging.
Early ability to gaze provides insights into cognitive development before verbalizations occur.
Eye Tracking: Non-invasive technology to identify what infants focus on and for how long.
Increased looking indicates interest, surprise, or attention.
Building Life with Genes & Proteins
Genes: Chemical blueprints containing DNA.
DNA transcribes into RNA, which is used to synthesize proteins, essential for living beings.
Epigenetics: Determines which genes are activated.
Genetic information is organized within chromosomes, containing thousands of genes.
The Beginning of Life
Humans possess 46 chromosomes; gametes (sperm and ovum) each hold 23 chromosomes.
Upon fertilization, a complete set of chromosomes is established, including mitochondrial DNA, which acts as the cell's energy factory.
Twin Studies
Identical (monozygotic) twins: Result from a single fertilized ovum dividing, sharing identical genes.
Fraternal (dizygotic) twins: Arise from two fertilized ova, sharing about 50% of genes.
Insights into Heritability from Twin Studies
Higher concordance in identical twins compared to fraternal ones indicates a strong genetic basis for traits.
Similar concordance means significant environmental influences.
Genotypes vs. Phenotypes
Genotype: Inherited genetic makeup.
Phenotype: Expression of the genotype influenced by the environment.
Heterozygous: Different alleles for a trait (e.g., blue and brown eyes).
Homozygous: Identical alleles for a trait (e.g., both brown eyes).
Determining the Phenotype
Dominant genes override recessive genes in phenotype expression.
Example: Brown eyes (dominant) vs. blue eyes (recessive).
Chromosomal Abnormalities
Approximately 1% of U.S. infants have genetic or chromosomal conditions impacting physical/neurological health.
Huntington’s Disease:
Onset around age 35, characterized by jerky movements, cognitive impairment, and death; follows dominant inheritance on chromosome 4.
Phenylketonuria (PKU):
Recessive disorder causing lack of enzyme for digesting phenylalanine; untreated leads to severe intellectual disabilities.
Down Syndrome (Trisomy 21):
The most prevalent chromosomal disorder, presenting with characteristic physical features and varying levels of cognitive disability.
Prenatal Development
Occurs over approximately 9 months and comprises three stages:
Germinal Stage: First two weeks post-fertilization; zygote attaches to the uterine wall.
Developments: Amniotic sac, umbilical cord, placenta.
Embryonic Stage: Weeks 3 to 8; formation of vital organs and features; sensitive to teratogens.
Fetal Stage: From 9 weeks until birth; refinement of body features and systems.
Teratogens and Environmental Influences
Teratogens: Substances that negatively affect embryo/fetus development.
Routes of influence: Medication/drugs and their lipid solubility.
Notable disorder: Fetal Alcohol Spectrum Disorder resulting from alcohol exposure in pregnancy, leading to various cognitive and physical abnormalities.
Physical Development: Birth Through Childhood
At birth, nearly all neurons are present, though the brain is only 25% of adult weight.
Key developmental milestones of brain growth:
By 6 months: 50% adult brain size.
By 2 years: 75%.
By 5 years: 95%.
Brain development occurs in stages favoring early sensory regions and motor control.
Environmental Impacts on Brain Development
High neuroplasticity allows the developing brain to grow from environmental enrichment.
Enriched environments can lead to larger brain sizes in comparison with impoverished contexts due to increased neuron size and complexity of connections.
Physical Growth Patterns
Infants double their birth weight in the first six months and triple it in the first year; grow significantly in height too.
Growth rates slow post-3 years; approximately 2-3 inches annually until adolescence.
Motor Development
Babies initially possess involuntary reflexes critical for protection and nourishment.
Reflexes include rooting, startle (Moro), grasping (Darwinian), swimming reflex, reactions to various stimuli, and ability to place and withdraw feet.
More complex motor skills emerge as neurological development progresses; key milestones occur between 14-35 months.
Cognitive Development
Cognitive development concerns the ability to remember, perspective-taking, logical reasoning, and symbolic use.
Piaget’s Theory of Cognitive Development
Assimilation: Interpretation of new information within existing schemas.
Accommodation: Process of restructuring existing schemas to integrate new information.
Four stages:
Sensorimotor (birth ~2 years)
Preoperational (~2-7 years)
Concrete Operational (~7-12 years)
Formal Operational (12+ years)
Stages of Cognitive Development
Sensorimotor Stage: Learning through senses and gradual object permanence; facilitates basic logical reasoning.
Preoperational Stage: Symbolic thought begins; immature concepts and egocentrism prevalent.
Concrete Operational Stage: Logical operations start; mastering conservation and decentration; thinking remains limited to concrete contexts.
Formal Operational Stage: Development of abstract and deductive reasoning capabilities.
Psychosocial Development
Accompanying physical and cognitive growth, psychosocial development involves attachment formation, parenting impact, within the context of Erik Erikson's theory spanning eight stages.
Attachment
Emotional bond between infant and caregiver following a sequence:
Indiscriminate attachment (first 6-7 months): Positive social behaviors towards everyone.
Specific attachment: Babies' responsiveness escalates towards primary caregivers, leading to distress upon separation.
Separate attachments (12-18 months): Expanding interest beyond primary caregivers.
Harlow’s Landmark Attachment Studies
Study showed infant monkeys preferred contact comfort (cloth mother) over nourishment (wire mother with a feeding bottle).
Highlights that attachment is based on comfort, not solely feeding.
Impact of Attachment Deprivation
Motherless monkeys later rejected mating opportunities and struggled with nurturing offspring.
Harlow’s findings resonate with human studies of children raised in inadequate conditions, who face emotional and social difficulties unless provided with later nurturing.
Measuring Attachment: The Strange Situation
Mary Ainsworth's procedure assessed infant responses through varying parental presence.
Securely attached infants explore confidently but show distress when separated and happiness upon reunion.
Insecurely attached infants are hesitant to explore, display excessive distress, with varied responses to parental return ranging from anger to indifference.
Parenting Styles Impact on Development
Identified styles:
Permissive: Hands-off approach leads to immature, impulsive, and dependent children.
Authoritarian: Strict rules and expectations foster indecisive and less curious offspring.
Authoritative: Balanced structure and responsiveness promote well-adjusted children with a sense of agency.
Cultural Differences in Parenting Styles
Parenting impacts can be culturally specific; some cultures value individual independence while others prioritize family and community respect.
Erikson’s Psychological Development Theory
Consists of eight stages covering the entire lifespan, assessing the tension between various individual goals and societal expectations:
Trust vs. Mistrust
Autonomy vs. Shame/Doubt
Initiative vs. Guilt
Industry vs. Inferiority
Identity vs. Role Confusion
Intimacy vs. Isolation
Generativity vs. Stagnation
Ego Integrity vs. Despair
Language Development
Language constitutes a symbolic system for communication, encompassing rules that structure how symbols combine.
Psycholinguistics: The discipline studying how sounds and symbols convert into meaning, analyzing five levels of language:
Phonemes
Morphemes
Syntax
Semantics
Pragmatics
Stages of Language Acquisition
Early vocalizations: From cooing to babbling around 6 months.
First words: Approx. 1 year; initial words carry broader meanings.
Condensed speech: 1-2 years; production of simple sentences.
Expanded language: Rapid vocabulary growth and complex sentence construction after age 2.
Language in the Brain
Major areas include:
Broca’s Area: Responsible for language production; damage leads to Broca’s aphasia.
Wernicke’s Area: Involved in language comprehension; damage results in Wernicke’s aphasia.
Adolescence
Marked by physical and psychosocial transformations, including hormonal changes that impact growth and secondary sex characteristics.
Cognitive Development in Adolescence
Enhanced problem-solving skills align with cognitive stages laid out by Piaget and moral reasoning evolving through Kohlberg’s levels.
Adulthood
Peak physical capacities occur in twenties-thirties; thereafter, sensory and cognitive declines commence unless actively mitigated by lifestyle choices.
Successful Aging
Despite declines, life satisfaction tends to peak later in life; exercise and social engagement are crucial in maintaining quality of life.
Roseto Effect: Highlights the role of community in health outcomes, exhibiting lower disease rates despite high-risk lifestyles, attributing outcomes to social support and lower stress levels.