The baby's "feeling of himself" first arises in the midst of the earliest interactions with his parental partner, establishing his 'drive monatges' whose acomplishment forms a circuit latching on to something in the first other. In the course of these early interactions, the 'new subject' evoked by Freud will gradually take on its own qualities.
The condition of the human subject demands that he acquire his existence at the price of a real passion. And what indeed could inspire more passion than this ambiguous being, constantly trying to balance dynamically where nature and of culture intersect?