Determinants of Intelligence

Have you ever wondered why siblings sometimes differ sharply in intelligence, even though they share parents and a home? Psychologists explain these individual differences using two powerful forces: heredity (nature) and environment (nurture).

• Intelligence is influenced by genes inherited from biological parents.
• Heredity sets the upper and lower limits ("potential range") of intellectual ability.
• Example: Identical twins separated at birth often show similar IQs, revealing the strong influence of genetics.

• Environment means all external influences - family, education, nutrition, culture, and social opportunities.
• A stimulating, healthy environment enables a person to approach their genetic potential.
• Example: Nutrition, educational quality, and family support all make a measurable difference to IQ.

Neither heredity nor environment alone determines intelligence. Both interact continuously.

Diagram explanation:
Heredity sets a range (as if marking the boundaries of a track), while environment determines the position (like a runner’s final spot within those lanes).

• The “Flynn effect”: Average IQ scores have risen over the last century thanks to better education, nutrition, and living conditions, not changes in genetics.
• Adoption studies: Children from deprived environments adopted into enriched families show marked IQ improvement, highlighting environmental effects.

• Intelligence develops through the interaction of genetics (heredity) and life experiences (environment).
• Heredity sets the possible range, while environment determines the outcome within that range.
• Both strong genetics and healthy environments are important for intellectual growth.