Lewis-Williams begins with a fascinating history of the study of these images. I was surprised to find how important Marxism had been to this study, and the author's analysis of the strengths and weaknesses of various approaches, including that of famous thinkers like Claude Levi-Strauss is a useful introduction to their ideas.
Lewis-Williams argues that while art varies in terms of meaning and use through history, and indeed how we perceive things such as the colour spectrum is socially determined, there is one universal for anatomically modern humans, which is that we all (and we all have) experience a the same "full spectrum of consciousness". Describing the various stages that people go through in altered consciousness states, Lewis-Williams points out that "all people experience the states characteristic of the autistic trajectory. And they experience them in terms of their own culture and value system; this is what has been called the 'domestication of trance'."
Lewis-Williams argues that this means that we can trace some universals to the images on cave-walls, and understand them in terms of how various cultures have related to states of altered consciousness. Discussing the San people who made rock painting into the modern time, as part of shamanistic religion, he points out that
Much of the painted and engraved imagery, even that which appears relastic' is shot through with these metaphors and shows signs of having been 'processed' by the human mind as it shifted back and forth along the spectrum of consciousness. The same metaphors necessarily structured the explanations of images that San people provided. The San explained the images in their own terms, not the languages of anthropologists.So the images made by the San people represented things that meant some thing to them collectively, which is not necessarily the same thing that we might "see" when we look at them. But because altered states, or trances, produced visions that the mind interprets in terms of how the world is understood, the images painted would be of things (or shapes) that originated in their world view.
Art, cosmos and spiritual experience coalesced. The San fused the 'abstract' experiences of altered states with the materiality of the world in which they lived.So the paintings made in the "social space" of the caves were the result of interactions between the social ideas of the group and their world-view. Lewis-Williams argues that this meant that the images were more than images, they were insights into a spirit world, or actual embodiments of that world over-lapping with the contemporary world. He writes that a "set of animals already carried... symbolic meaning for west European anatomically modern communities. It now became important for those people to fix their images of another world, belief in which was one of the key traits that distinguished them from the Neanderthals."
Lewis-Williams argues that it was the process of doing this, creating the art, that paved the way for new social relations that "we consider fully modern". I remained unconvinced by this conclusion, as I think the "images" are more likely to represent the cultural output of a community and thus reflect social relations rather than create them. But as Lewis-Williams correctly points out, we cannot every know a correct answer when trying to understand what the images mean. His book however is a fascinating insight into the reasons that humans have created cave-art and painting through history and by hunter-gatherer communities in modern times. It is well worth a read.
Mithen - After the Ice: A Global Human History
Stringer - The Origin of Our Species