The publication by Meaney and Szyf (2005) describes how early environmental influences—particularly parental care—have long-lasting effects on the regulation of the stress system. Their work is based on animal research, especially in rats, and shows that differences in maternal behavior (such as licking and grooming) cause lasting changes in the stress response of offspring.

Central to this is the hypothalamic-pituitary-adrenal axis (HPA axis), the system that regulates the production of stress hormones such as cortisol (in humans). Rat pups that receive a lot of care develop a more efficient negative feedback in this system. This means that their stress response calms down more quickly. Pups that receive less care, on the other hand, show an increased and longer-lasting stress response.

According to the authors, the key to these differences lies in epigenetic mechanisms, particularly DNA methylation. They demonstrate that maternal behavior influences the methylation of the gene encoding the glucocorticoid receptor in the hippocampus. More care leads to less methylation and thus to higher gene expression, resulting in better stress regulation. Less care produces the opposite effect.

Remarkably, these changes remain stable into adulthood but are not immutable. Experimental interventions were able to partially reverse the epigenetic markers. With this, Meaney and Szyf underscore that genes do not determine a fixed fate: environmental influences “program” biological systems, but plasticity persists.

The study provides fundamental evidence that early experiences leave biological traces that influence behavior and stress sensitivity. The work formed an important basis for subsequent studies into the intergenerational transmission of stress and trauma in humans.