A central topic in behavioral biology is the question, which aspects of a behavior are learned or expressed due to genetic predisposition. Today it is known that our personality and behavior are far less determined by the genetic background. Especially during development environmental factors can shape brain and behavior via so-called epigenetic effects. Thereby hormones play an important role. netic predisposition. However, it is relatively hard to discriminate the effects of the environment from that of the genes.