During the first years of life, what will be the bases of human condition is made up –the whole of it is subject to an interaction between heredity and environment’s effects. In this work –which addresses both graduate and non-graduate students–, the author presents general theories and biological bases of memory, language, problem solving, rationing, school skills, temperament, attachment, genre, the ego, development of spatial cognition and perception, cognitive development…, with theoretical perspectives and styles of both classical and nowadays research.