spontaneous

Happening or arising without apparent external cause; self-generated.

Arising from a natural inclination or impulse and not from forethought or prompting.

Unconstrained and unstudied in manner or behavior.

Growing without cultivation or human labor.

Proceeding from a conscious or unconscious internal impulse; occurring or done without the intervention of external causes; in a restricted sense, springing from one's own desire or volition, apart from any external suggestion or incitement.