Chapter 10 – Human Development: Physical and Motor Development

Human Development

Introduction to Developmental Psychology

Developmental psychology is the scientific study of how behaviour and mental processes change over the lifespan. It explores the dynamic interplay between biological, cognitive, and social factors as individuals progress from conception to adulthood and beyond.

• Key Point: Focuses on changes and continuities in behaviour and mental processes across different life stages.

• Example: Studying how language acquisition evolves from infancy to adolescence.

10.1 Special Considerations in Human Development

Post Hoc Fallacy

The post hoc fallacy is a logical error where one assumes that because event A precedes event B, A must cause B. This reasoning is tempting when earlier behaviour seems logically related to later outcomes, but it can lead to incorrect conclusions about causality in development.

• Key Point: Correlation does not imply causation, especially in developmental sequences.

• Example: Assuming that early reading leads directly to higher intelligence without considering other factors.

Bidirectional Influences

Human development is shaped by two-way interactions. Children's experiences influence their development, and their development also affects their experiences. Parents, siblings, and teachers all play roles in this bidirectional process.

• Key Point: Developmental influences are reciprocal, not one-directional.

• Example: A child's temperament affects parental behaviour, which in turn influences the child's further development.

Keeping an Eye on Cohort Effects

Cohort effects refer to differences that arise from the unique experiences of groups of people born and living during the same time period. These effects can confound developmental research if not properly controlled.

• Key Point: Cohort effects must be considered when comparing people of different ages.

• Example: Comparing technology use between generations may reflect cohort effects rather than developmental changes.

Research Designs in Developmental Psychology

Design	Description
Cross-sectional	Examines people of different ages at a single point in time, providing a "snapshot" of age-related differences.
Longitudinal	Tracks the same group of subjects over time, allowing for the study of true developmental changes within individuals.

Issues with Longitudinal Designs

Longitudinal studies are ideal for tracking change but can be costly and time-consuming. They are also subject to attrition (participants dropping out) and selective attrition (dropout rates differing by group).

• Key Point: Attrition can bias results, especially if certain groups are more likely to drop out.

• Example: Older adults or minority groups may be underrepresented in long-term studies.

The Influence of Early Experience

Two common myths in developmental psychology are infant determinism (the belief that early experiences are overwhelmingly influential) and childhood fragility (the idea that children are easily damaged).

• Key Point: Later experiences can also be important, and children are often more resilient than assumed.

• Example: Many children recover from early adversity and thrive in supportive environments.

Clarifying the Nature–Nurture Debate

Both genetic (nature) and environmental (nurture) factors interact to shape development. Their effects are complex and intertwined.

Nature–Nurture Interaction	Definition
Gene–Environment Interaction	The impact of genes on behaviour depends on the environment in which the behaviour develops.
Nature via Nurture	Genetic predispositions can lead us to seek and create particular environments, leading to the mistaken appearance of a pure effect of nature.
Gene Expression	Some genes "turn on" only in response to specific environmental events.

Gene–Environment Interaction

Genes and environment interact throughout development. The effect of one depends on the contribution of the other.

• Key Point: Genetic predispositions may only manifest in certain environments.

• Example: Children with a genetic risk for antisocial behaviour may only develop problems if exposed to adverse environments.

Nature Via Nurture

Children with certain genetic predispositions often seek out and create their own environments. For example, highly fearful children may seek environments that protect them from anxiety.

Gene Expression

Environmental experiences can activate or deactivate genes throughout development. Stressful events may trigger the expression of genes related to anxiety or other traits.

10.2 The Developing Body: Physical and Motor Development

Conception and Prenatal Development: From Zygote to Baby

Prenatal development is the period before birth, beginning with conception and progressing through three main stages:

• Germinal Stage: The zygote begins to divide and form a blastocyst. Around the middle of the second week, cells begin to differentiate.

• Embryonic Stage: From the 2nd to the 8th week, major organs and features begin to take shape.

• Fetal Stage: From the 9th week onward, major organs are developed and the heart begins to beat.

Brain Development

Unlike most organs, the brain continues to develop after birth. Between the 18th day of pregnancy and the end of the sixth month, neurons begin developing at a rapid rate, with up to 250,000 cells per minute during peak periods.

Obstacles to Normal Fetal Development

• Teratogens: Environmental factors (e.g., drugs, alcohol) that negatively impact prenatal development.

• Genetic Disorders: Random errors in cell division can cause adverse effects.

• Prematurity: Infants born before 36 weeks are at higher risk for health complications.

Infant Motor Development: How Babies Get Going

Infants are born with a set of automatic motor behaviours or reflexes that are triggered by specific types of stimulation and fulfill important survival needs.

• Sucking Reflex: Automatic response to oral stimulation; babies clamp down and begin sucking.

• Rooting Reflex: Stroking a hungry infant's cheek causes them to turn their head and begin searching for food.

Learning to Get Up and Go: Coordinating Movement

Motor milestones are healthy markers that occur in a set order but at different times for different children. These milestones include sitting, crawling, standing, and walking, reflecting the development of muscle and bone coordination.

• Key Point: The age at which children reach milestones varies, but the sequence is generally consistent.

• Example: Most children crawl before they walk.

Physical Maturation in Adolescence: The Power of Puberty

Adolescence is the transitional period between childhood and adulthood, marked by physical maturation and the attainment of reproductive potential.

• Primary Sex Characteristics: Changes in reproductive organs and genitals.

• Secondary Sex Characteristics: Sex-differentiating traits not directly related to reproduction, such as breast enlargement, deepening voices, and pubic hair.

• Menarche: The start of menstruation in females.

• Spermarche: The first ejaculation in males.

Activity – Physical Changes in Adulthood: Fact or Fiction?

Physical changes continue throughout adulthood, but common beliefs about aging may not always be accurate. Critical evaluation of these beliefs is important for understanding adult development.

Additional info: These notes expand on the original slides and handwritten content, providing definitions, examples, and structured explanations suitable for college-level psychology students.