Intellectual development is the product of a complex interplay of hereditary factor (nature) and environmental conditions (nurture). Heredity sets the range and environment shapes the development.
Nature (Hereditary factors): The most convincing evidence comes from twin studies and adoption studies. influences intelligence.
| Studies | Correlation |
| Identical twins reared together | 0.90 |
| Identical twins reared in different environments | 0.72 |
| Fraternal twins reared together | 0.60 |
| Siblings reared together | 0.50 |
| Siblings reared apart | 0.25 |
Nurture (Environmental factors): Evidence for environmental influences on intelligence comes from the following observations: Adoption studies demonstrate that adopted **** show some similarity in IQ to their adoptive parents.IQ declines over time in **** raised in deprived environments. Conversely, IQ improves in **** who leave deprived environments and enter enriched environments. Family background and socio-economic status; Nutrition; Schooling etc.
