Word with human or second

… NATURE

Think of a term that describes inherent qualities or instincts, often paired with "human" to discuss behavior or "second" to imply something acquired.

This clue plays on two possible meanings of "second." One is the adjective "second" as in "second nature," a phrase meaning something that feels instinctive. The other is "second" as in the word following "human" in "human nature." The answer is the last part of that phrase, so you drop "human" and keep "nature.