spontaneous
     adj 1: happening or arising without apparent external cause;
            "spontaneous laughter"; "spontaneous combustion"; "a
            spontaneous abortion" [syn: {self-generated}] [ant: {induced}]
     2: said or done without having been planned or written in
        advance; "he made a few ad-lib remarks" [syn: {ad-lib}, {unwritten}]
     3: produced without being planted or without human labor; "wild
        strawberries" [syn: {wild}]
Source: WordNet® 2.0