Almost always both.<p>Environment triggers changes in gene expression and reverse is also true. There are multiple ways of how nature and nurture interact.<p>Take for example stress during childhood. It seems that stressful environment leads epigenetic changes an behavioral changes like lower impulse control, aggressive or more promiscuous behavior.<p>Is the change in behavior damage caused by the environment, or is it evolutionary adaptation to uncertain and dangerous environment? It's possible that dangerous environment triggers different epigenetic survival strategies? Breed faster, be more aggressive and do quick decisions.<p>Differentially Methylated Genes in Saliva are linked to Childhood Stress
<a href="https://www.nature.com/articles/s41598-018-29107-0" rel="nofollow">https://www.nature.com/articles/s41598-018-29107-0</a>