"Second Nature"
My child asked once where the phrase "second nature" came from. Also...what would be one's "first" nature
Kim
SECOND NATURE -- "Said of a habit or way of doing things that has become so ingrained that it is instinctive." From Brewer's Dictionary of Phrase and Fable revised by Adrian Room (HarperCollinsPublishers, New York, 1999, Sixteenth Edition).
The first nature would be those things we are genetically programed to do, like, the song says: "breathing out and breathing in."