Genetic Bases of Development - Personality

Personality refers to the combination of thoughts, feelings, and behaviors that make each person unique. Heredity means the passing of traits from parents to children through genes and chromosomes. Psychologists believe that heredity plays an important part in shaping certain aspects of personality, such as temperament and emotional tendencies. However, environment and life experiences also influence how these inherited traits are expressed in real life.

Scientists have tried to find out whether heredity influences behaviors such as aggression, introversion, and extraversion.
The results show that:

• Some people show repeated acts of violence or aggression, which may have a biological link.
• A study of very tall male prisoners found that about 10% had 47 chromosomes (XXY or XYY) instead of the normal 46.
• In the general public, such an abnormality is present in only 1% of people.

This suggests heredity may influence some tendencies, but genes alone cannot explain behavior. Life experiences, family environment, and social factors play important roles.

To understand how much behavior is affected by genes, psychologists compare identical twins and fraternal twins.

Results show that some traits, like shyness or sociability, have genetic roots, though the environment affects how they grow.

Research suggests heredity partly influences these personality traits:

• Introversion: Being quiet, thoughtful, and shy.
• Extraversion: Being lively, outgoing, and friendly.

These traits are part of Eysenck’s biological theory of personality, where genetics and environment together shape who people become.​

Two brothers brought up in the same home may still be different:

• One enjoys parties and talking to people (extrovert).
• The other prefers staying alone and reading (introvert).

Though their environment is the same, their genetic makeup creates differences in behavior.

• Heredity and environment work together in forming personality.
• Genes provide basic tendencies, but surroundings shape their expression.
• No single gene causes a particular behavior — all traits are results of interaction.
• Twin studies and chromosomal research help show how behavior has biological roots.
• The introversion–extraversion dimension is partly genetic.