In nonhuman mammals, the social environment in which pregnant females live is critical for their offsprings' behavioural and brain development, reproductive functioning and endocrine state later in life: social instability during pregnancy, for example, generally brings about a behavioural and neuroendocrine masculinisation in daughters and a less pronounced expression of male-typical traits in sons. These effects of prenatal social stress are not necessarily "pathological" (non-adaptive) consequences of adverse social conditions. Rather, pregnant mothers could be adjusting their offspring to the environment in which they live during pregnancy in an adaptive way. The central hypothesis of this project is that in stable social environments offspring of mothers who lived in a stable social environment during pregnancy will have benefits in terms of direct measures of fitness over offspring of mothers, who lived in an unstable social environment during this period of life. Accordingly, the reverse is expected if the offspring is living in an unstable social environment. This project may contribute in an outstanding manner to the question whether behavioural and physiological traits shaped by social factors during the prenatal phase can be adaptive.