Prenatal and early postnatal influences on measured intelligence.

Area of Science:

• Human Physiology
• Developmental Biology
• Evolutionary Biology

Background:

• Natural selection favors reduced litter size and longer gestation in mammals.
• Human pregnancy, typically single, extends beyond optimal fetal growth support.
• Extended gestation may confer advantages like enhanced immunity at birth.

Purpose of the Study:

• To investigate the relationship between prolonged gestation and fetal growth.
• To determine the effect of prenatal growth retardation on measured intelligence.
• To explore the influence of postnatal factors on cognitive development.

Main Methods:

• Comparative analysis of prenatal and postnatal growth rates.
• Examination of verbal reasoning scores in relation to birth weight and gestation duration.
• Comparison of cognitive scores between twins raised together and separately, and single births.

Main Results:

• Prolonged gestation does not negatively affect measured intelligence, despite potential fetal growth limitations.
• Differences in cognitive scores related to birth weight, gestation, maternal age, and birth order are not observed within siblings.
• Twins raised apart show higher verbal reasoning scores than those raised together, indicating the impact of postnatal environment.

Conclusions:

• Extended human gestation is likely an evolutionary adaptation for improved postnatal survival, not cognitive enhancement.
• Postnatal experiences play a crucial role in shaping verbal reasoning abilities, outweighing prenatal growth effects.
• The cognitive differences observed between singletons and twins are primarily attributable to postnatal environmental factors.