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Determinants of Intelligence - Hereditary Factors

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Topics

  • Introduction
  • Main Studies and Evidence
  • IQ and Heredity Studies
  • Real-Life Application
  • Key Point Summary
CISCE: Class 12

Introduction

Heredity refers to the genetic transmission of traits - including intelligence - from parents to offspring. Scientists study twins and family members to understand how strongly genes affect intellectual ability versus environmental factors.

CISCE: Class 12

Main Studies and Evidence

Twin Studies:

  • Identical Twins (Monozygotic): Share 100% of genes.
  • Fraternal Twins (Dizygotic): Share 50% of genes.

Key Research:

  • Newman, Freeman & Holzinger (1937): Compared identical twins raised apart; their IQ scores were extremely similar—suggesting genes matter most.
  • Shields (1962): Studied 88 pairs of identical twins (half raised together, half apart). IQ correlations: 0.77 (together), 0.76 (apart); again, genes played a larger role than upbringing.
  • Other studies: Even with environmental changes, IQ usually remains stable after early childhood.
CISCE: Class 12

IQ and Heredity Studies

CISCE: Class 12

Real-Life Application

Imagine baking two cakes using the same recipe but in different ovens. If both taste alike, it's the recipe (genes), not the oven (environment), that’s most important.

CISCE: Class 12

Key Point Summary

  • Identical twins have highly similar intelligence, whether raised together or apart.
  • Family IQ correlations are much higher than those between unrelated people.
  • Genetic (hereditary) influence on intelligence is stronger than most environmental effects after early childhood.
  • Intelligence differences in populations still involve both genetic and environmental factors.

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