Individual differences in cognition, emotion, and behaviour develop during ontogeny. Using a comparative approach, this contribution focuses on the modulation of behavioural profiles by the social environment in mammals. I review evidence that such shaping of behavioural profiles occurs from the prenatal phase through adolescence and beyond. Causation is discussed, in particular, how behavioural profiles are shaped by social stimuli through behavioural and neuroendocrine processes. Finally, function is addressed and it is argued that the shaping of behavioural profiles by social experience represents an effective mechanism for repeated and rapid adaptation during the life time.