Biological and environmental initial conditions shape the trajectories of cognitive and social‐emotional development across the first years of life

Human development is thought to evolve from the dynamic interchange of biological dispositions and environmental provisions; yet the effects of specific biological and environmental birth conditions on the trajectories of cognitive and social‐emotional growth have rarely been studied. We observed 126 children at six time‐points from birth to 5 years. Intelligence, maternal sensitivity, and child social engagement were repeatedly tested. Effects of neonatal vagal tone (VT) and maternal postpartum depressive symptoms on growth‐rates were assessed. Cognitive development showed a substantial growth‐spurt between 2 and 5 years and social engagement increased rapidly across the first year and more gradually thereafter. VT improved cognitive and social‐emotional growth‐rates across the first year, whereas maternal depressive symptoms interfered with growth from 2 to 5 years. Differences between infants with none, one, or two non‐optimal birth conditions increased with age. Findings shed light on the dynamics of early development as it is shaped by biological and environmental initial conditions.