A new comparative analysis across mammals brings order to previously ambiguous results on the effects that maternal stress has on the developing offspring. Different studies (often on the same species) have reported that early adversity enhances, hampers, or has no effect on offspring development and performance. Researchers from the German Primate Center and Universities of Göttingen and New Mexico have now proposed a hypothesis that largely predicts such highly variable patterns in the growth rates of disadvantaged offspring across 719 studies on 21 mammal species. “The idea is that prenatal stress affects offspring in two different ways depending on the timing of the stressor during pregnancy – yielding different outcomes before birth, after birth, and after weaning” says Andreas Berghänel, the lead author of the study. The study was published in the journal PNAS.