I read this book years ago and have never been able to find it, can anybody help. Aliens land on him accidentally, and one of them repairs the damage and adds a little something extra. The character grows a new leg after a cave lion rips it off, and returns to his tribe, becoming a shaman with the ability to alter his physical being, discovers he never ages, goes through all of human history, survives aztec sacrifice attempt by growing a second heart while his is cut out, world war 2 interacts with hitler, many other forest gumplike adventures, all the while pondering his uniqueness, finally entering space age and becoming one with the universe or something, at last realizing the origins of his powers.