This writer is not a disturbingly deep thinker. That is why the breezily narrated travel stories and able recapitulation of myths and religious beliefs from all over the world of import to the book's thesis gives way to great uncertainty (and countless "I feel as if..." and "I believe...") whenever it is time to draw some conclusions from the gathered factoids.
Had he been even better read-up on ancient religious practice and more versed in philosophical thinking the reader would have been spared the programmatic and (as used) shallow phrase "life and death", repeated throughout without any fleshing out. The writer seems not be able to approach such a weighty theme and the theorizing concerning shamanic practices suffers accordingly. Make no mistake, the book was quite readable, but fell apart when it was time for the theory itself to speak up.
The attempt to come to grips with why shamans of the past would have entered remote and inaccessible caves also strikes me as just about the silliest I have ever read in this genre. (The company tags this book as "History" - a fraud if there ever was one!) And yet the author has the solution to the "cave mystery" within sight, having talked about the symbolic value inhering in the female genitals throughout. It appears he doesn't realize he has already "solved" the mystery, since he mentions the task of solving of the cave riddle long after having presenting a summary on Egyptian religious beliefs. For some real, groundbreaking thinking, see Peter Kingsley's highly acclaimed Ancient Philosophy, Mystery and Magic. It deals incomparably better with the topic. Hint: the cave or dug pit into which the shaman withdraws is easily understood in terms of ritual death, burying and spiritual rebirth.
On the other hand I think he is onto something as far as the constellation Cygnus is concerned. I do buy into the idea of the capability of mankind to diffuse and then preserve traditions as Collins notes apropos the naming of certain postures in the martial arts. The bit about the age during with the Chinese star map would have made sense is absolutely thrilling when pondered upon.
But then there are also the occasional hint within the book that some of the ideas were the fruit of lazy Internet research; checking up on the basis for author's siding with the suggestion that Nobel prize winner Francis Crick was high on LSD when discovering the DNA double helix, I soon found that ONE sensationalistic (never corroborated) report. But I also noted another side of the question, seemingly carrying more weight: the issue of whether Crick and Watson filched important parts of the theory from another scientist. I do agree with the author that psychoactive plants do have mind changing properties, but using rumours as fact will not help the writer's argument.
In all fairness, the book presents many an interesting fact, all on loan from other thinkers, and this book served me best as a pointer to one or two real scientists and their theories. Given the central idea that human evolution was speeded-up by some intensive showers of cosmic radiation, it is a pity the author weren't around then to receive a sprinkle of it himself. :-)
The biggest laugh of this book was the notion that the cosmic rays at one time way back was extremely strong, but that the shamans cleverly hid themselves inside the rock caves to "filter" the radiation and so benefit from the "evolutionary rays" and thereby furthered themselves even more. Do you find that a bit hard to digest, you may want to pass on this title because that seems to be the bottomline: the white shamans in the northern hemisphere were the first to develop (and spread) modern intelligence, presumably not too dissimilar from the author's own.