Predictions of children's emotionality from evolutionary and epigenetic hypotheses

Abstract

Sex-dependent effects of mismatched prenatal-postnatal maternal conditions are predicted by combining two evolutionary hypotheses: that foetal conditions provide a forecast of likely postnatal environments (Predictive Adaptive Response), and that the female foetus is better adapted than the male to maternal adversity (Trivers-Willard hypothesis). Animal studies have implicated glucocorticoid mechanisms modifiable by effects of postnatal tactile stimulation on glucocorticoid receptor gene expression. In this study we examined behavioural predictions in humans based on these evolutionary and epigenetic models. Mothers in a general population cohort provided self-reported anxiety scores at 20 weeks pregnancy, and at 9 weeks, 14 months and 3.5 years postpartum, and frequency of infant stroking at 9 weeks. Mothers and teachers reported child symptoms at 7 years. SEM models with maximum-likelihood estimates made use of data from 887 participants. There was a three-way interaction between prenatal and postnatal anxiety and maternal stroking in the prediction of irritability, seen only in girls. This arose because lower maternal stroking was associated with higher irritability, only in the mismatched, low-high and high-low maternal anxiety groups. We provide evidence that mechanisms likely to have evolved well before the emergence of humans, contribute to the development of children's emotionality and risk for depression.

Figure 1

Summary of SEM for prediction of child irritability, accounting for general psychopathology, from prenatal and postnatal maternal anxiety and stroking. Main effects are shown in black, interactions in red and potential mediation of effects via general psychopathology ‘p’ in blue. Correlations among all observed predictor (exogeneous) variables are not shown.

Figure 2

Associations between maternal stroking at 9 weeks and child irritability at 7 years, in matched and mismatched prenatal and postnatal maternal anxiety groups. In the left hand panel the dotted regression lines show the association between maternal stroking age 9 weeks and irritability at age 9 years in each mismatched maternal anxiety group (low prenatal - high postnatal; high prenatal - low postnatal) and the solid lines in each matched group (low prenatal - low postnatal; high prenatal - high postnatal). The groups were generated using medians of the maternal anxiety distributions. The right hand panel shows the regression lines and 95% confidence intervals in the combined mismatched and matched groups.