The "concept" of shamanistic thought or more "real"istically non thought has to be learnt by the majority of folk not being given the blessing naturally. A lot of folk havn't the function for objective being, so to experience this state, nature or the "world" closest to man, has given us a short cut to realize this state (albeit for a short period) and to gain knowledge from it, to maybe realize its true understanding.
Only when those unblessed have something tangible to use as a goal can the knowledge be understood, hence graham hancocks use of his shortcuts to taste the hidden depths of mans conciousness can only inspire him to become more spiritual, and this can be seen as he descibes each journey in this book.
The cave drawings act only as a subjective trigger to his realization, probably for which they were designed. :)