5. T2: Nature, Nurture, and Human Diversity

Francis Galton

An English scientist (1822–1911) who pioneered research on heredity and individual differences. He coined the term “nature versus nurture” to describe the debate over whether traits are shaped more by genetics or environment. Galton emphasized the role of heredity in intelligence.

Hereditary Genius (book)

A book written by Francis Galton in 1869, arguing that intelligence and talent are inherited traits passed down through families.

Central Dogma of Genetics

DNA → mRNA → Protein.

Genome

The complete set of genetic material (DNA) in an organism, including all of its genes and noncoding sequences. The genome contains all the instructions needed to build and maintain that organism.

Nature

A behavior, personality trait, cognitive ability, or form of psychopathology that is primarily due to a person’s genes.

Nurture

A behavior, personality trait, cognitive ability, or form of psychopathology that is primarily due to a person’s environment.

Polygenic

Refers to a trait that is influenced by multiple genes, rather than a single gene. Most complex human traits—such as intelligence, personality, sexual orientation, and mental disorders—are polygenic, meaning many genes work together to shape their expression.

Identical (Monozygotic) Twins

Identical twins develop from a single fertilized egg. They are virtually 100% genetically identical. Sometimes identical twins do not share the same placenta (30% of the time).

Fraternal (Dizygotic) Twins

Develop from two separate fertilized eggs. They are not more genetically similar than ordinary siblings (50% genetically identical) despite sharing the same prenatal environment.

Heritability

The percentage or proportion of variance of a specific trait that is attributable to genetics.

Variation

The differences or diversity in traits among individuals within a population, often caused by genetic factors, environmental influences, or their interaction. Variation is essential for evolution and helps explain why individuals are not all the same.

Competition

The struggle among organisms for limited resources—such as food, space, or mates—which affects their ability to survive and reproduce.

Differential Survival

The process by which individuals with favorable traits are more likely to survive, reproduce, and pass on those traits to the next generation, leading to evolutionary change over time.

Natural Selection

The process whereby organisms better adapted to their environment tend to survive and produce more offspring.

Sexual Selection

Selection arising through preference by one sex for certain characteristics in individuals of the other sex.

Evolutionary Psychology

Theoretical approach to psychology that attempts to explain useful mental and psychological traits as functional products of natural and sexual selection.

Clark & Hatfield (1989)

A famous psychology study on gender differences in sexual behavior. Male and female college students were approached by strangers who asked them to go on a date, come to their apartment, or have sex. Nearly all men agreed to casual sex, while no women did.

Buss & Schmitt (1993)

Proposed the Sexual Strategies Theory, which argues that men and women evolved different mating strategies based on reproductive challenges. Men tend to favor short

Sexual Dimorphism

Distinct difference in size or appearance between the sexes of an animal, not counting differences in their sex organs.

Tournament Species

A species in which one sex (typically males) competes to mate. Most members of the competing sex never win and never mate, while almost all members of the other sex mate with a few winners.

Pair Bonding Species

A species in which males and females form pair bonds and remain relatively monogamous. Pair

Culture

The enduring behaviors, ideas, attitudes, values, and traditions shared by a group of people and transmitted from one generation to the next.

Norms

Understood rules for accepted and expected behavior. Norms prescribe “proper” behavior.

Tight Culture

Places with clearly defined and reliably enforced norms.

Loose Culture

Places with flexible and informal norms.

Individualism

A cultural pattern that emphasizes personal goals over group goals and defines identity mainly in terms of individual attributes. Common in countries like the United States, the United Kingdom, and Australia.

Collectivism

A cultural pattern that prioritizes the goals of important groups (like family or work) over personal goals. Common in countries like China, India, and Indonesia.

Sex

A biological term referring to the functional differences between males and females and their reproductive potential. Male, Female, and Intersex are biological categories.

Androgen Insensitivity Syndrome (AIS)

A genetic disorder in which someone who is genetically male (XY) is resistant to male hormones (androgens).

Hormones

Chemical messengers produced by endocrine glands that travel through the bloodstream and affect other tissues.

Androgens

Hormones that stimulate and control the development and maintenance of male characteristics. Testosterone is the most well

Estrogen

A class of hormones responsible for the female reproductive system and secondary sex characteristics. Androgens are a precursor for all estrogens.

Activational Effects

The effects of hormones on the adult organism’s behavior or physiology.

Organizational Effects

The effects of hormones during early development that shape long

Gender

In psychology, the behavioral and mental characteristics that people associate with being male or female.

Instrumental (Men)

Characterized by a tendency to take action and be competitive, independent, aggressive, and self

Expressive (Women)

Characterized by a tendency to be emotionally open, gentle, empathetic, cooperative, and concerned with the needs of others.

Social Learning Theory

The theory that people learn social behavior by observing and imitating others, and by being rewarded or punished.

Baby X Studies

Experiments in which a baby in gender-neutral clothing is introduced with either a male or female name. Participants treated “boys” more roughly and gave them trucks, while “girls” were treated more gently and given dolls.