erm, there's no such thing as 'natural language' it is ALWAYS ALWAYS culturally and ideologically loaded ALWAYS...just so that happens sign language is more accessiable and easier to use, doesnt mean its 'natural', it never is. "Second nature", maybe yes, but its never natural, even for deaf babies with Deaf parent , sign language isnt natural, never!.
true and im not saying this to make SL look wrong, English is never natural for hearing people, niether is French or German or Tongan.
Drawing is natural either, it is learned, or some might say gifted - well thats another story...
G