I have just finished reading The Mind in the Cave: Consciousness and the Origins of Art by David Lewis-Williams.
In this book, the author examines rock art from the upper paleolithic, and compares it with case studies of known art and shamanistic practices from the San people of southern Africa and American natives. The working hypothesis is that the known samples of rock art are depictions of hallucinations of “spirit animals” during altered states of consciousness promoted e.g. through hallucinogens or through music, dancing and breathing routines.
The evidence at hand are described practices among the San people and North American natives, and features of both ancient and near contemporary rock art that closely resembles sensory disturbances experienced during migraines, where the disturbances can be explained by the neural architecture of the part of the brain that interprets the sensory input, and therefore follows from biology. We can see the same type of features in rock art in sites as far apart as southern Africa, Europe and the Americas. This is evidence backing up the hypothesis that these features are results of human neurology, and result from shamanistic rituals that involve altered states of consciousness.
Additionally, I especially noted the following, where the author quotes another researcher: “[S]hamanism, the result of cultural adaptation to biologically based [altered states of consciousness], is the origin of all later religious forms.”
In all, this book was very interesting both from the perspective of a geek that is interested in archaeology-based prehistory, and from the perspective of an atheist that is interested in the origins of religion and superstition.
Edit: I should also mention that I found an error in this book, namely the assertion that matings of Homo Neanderthalensis and Homo Sapiens could not bring forth fertile offspring. This is demonstrably false, as shown by evolutionary geneticist and Nobel laureate Svante Pääbo(*) (Wikipedia), who among other things documented gene transfer from neanderthals to Homo Sapiens. However, Lewis-Williams’s book predates Pääbo’s results, so the error is quite forgivable.
(*) I can highly recommend Pääbo’s book Neanderthal Man: In Search of Lost Genomes