PSYC 220: Theories of Development – Biological, Evolutionary, and Genetic Foundations

Theories of Development

This guide summarizes foundational theories and biological bases of human development, focusing on genetic, evolutionary, and systems perspectives. Understanding these frameworks is essential for analyzing how nature and nurture interact to shape psychological growth across the lifespan.

Main Approaches to Development

• Biology/Evolutionary

• Psychoanalytic

• Learning

• Cognitive

• Systems

Each approach offers a unique lens for understanding the origins and progression of human behavior and mental processes.

Biological/Evolutionary Foundations

Genetic and Epigenetic Factors

Biological and epigenetic factors interact with the environment to influence health, wellbeing, and development. Genetic and physiological processes underlie human behavior and psychological traits.

• Genetics is the study of inherited traits, including the role of DNA in shaping individual physical and behavioral characteristics.

• Epigenetics examines gene regulation and the influence of environmental factors on gene expression, affecting both physical and behavioral outcomes.

Basic Genetic Concepts

• Human cell nuclei contain 23 pairs of chromosomes.

• Each chromosome is made of DNA and divided into segments called genes.

• There are approximately 20,000–22,000 genes in each cell nucleus.

• Each gene occupies a specific locus (location) on a chromosome, consistent across individuals of the same species.

Genotypes and Phenotypes

• Genotype: The specific genetic material present on an individual's chromosomes.

• Phenotype: The observable characteristics or traits of an individual, resulting from the interaction of genotype and environment.

Example: A person may have the genotype for brown eyes (genetic code), but the phenotype is the actual eye color observed.

Patterns of Inheritance

• Dominant-Recessive Inheritance: A single dominant gene can determine a trait, while two recessive genes are needed for the recessive trait to appear.

• Polygenic Inheritance: Many genes contribute to a single trait (e.g., height, intelligence).

• Multifactorial Inheritance: Traits are influenced by both genes and environmental factors.

• Biparental Inheritance: Children inherit genes from both the mother (egg) and father (sperm).

Table: Sources of Traits

Dominant Genes	Recessive Genes	Polygenic (many genes)
Thick lips	Thin lips	Height
Dimples	Flat feet	Eye colour
Curly hair	Straight hair	Body type
Type A blood	Type O blood	Skin colour
Rh-positive blood	Rh-negative blood	Personality
Brown hair	Blond hair
	Red hair

Epigenetics

• Epigenetic markers regulate gene expression by signaling genes to "turn on" or "turn off." These mechanisms are influenced by environmental experiences.

• Epigenetic changes can be heritable and may increase the risk for certain physical and psychological disorders.

• Gene expression can be modified throughout the lifespan and passed to the next generation.

Example: Exposure to stress or toxins during pregnancy can alter gene expression in the developing fetus, potentially affecting health outcomes later in life.

Key Evolutionary Theories

• Ethology: The study of genetically determined survival behaviors that have evolved through natural selection.

• Behaviour Genetics: Examines how genetic differences contribute to behavioral differences, often using twin and adoption studies.

• Evolutionary Psychology: Focuses on how inherited cognitive and social traits have evolved to promote survival and reproduction.

Example: Infants are born with reflexes (e.g., sucking, grasping) that increase their chances of survival.

Additional info:

• Genetically inherited cognitive and social characteristics may appear at different stages of life, supporting adaptation to changing environments.

• Rather than being a "blank slate," humans are born with predispositions to learn and develop in certain ways.