As for the Blombos find. There is a far better interpretation than "tally" marks.
It is very unlikely that anyone was counting 75K years ago enough to have to record them.
There is a far more convincing and interesting interpretation concerning geometric patterns.
These are the forms you see if you are taking drugs, or in a trance state from dance or other ritual, or from sensory deprivation of the sort you get if you spend a long time in a cave.
Here's an extract from an essay I wrote a while ago. (Sorry I can't link the images)
Leroi-Gourhan's categories may be considered to be have a direct analogue with Ronald Siegel's three stages of trance: entoptic(pure geometric), construals (geometric figurative) and Iconics(synthetic figurative). Although such an idea would require more work it could demonstrate some fundamental propositions in art. In a natural landscape there are so few straight lines that it could be said that nature abores clean edges (exceptions, rock strata, horizons). The occurance of lines and geometric shapes in so called "primitive art" requires explanation which is provided by entoptic theory. This holds that geometric shapes derive from the fundamental neurophysiological structure of the visual cortex. These shapes can be "seen" at times when the normal visual work of the nervous system is interrupted such as: concussion, under the influence of drugs, extended periods of visual depravation, and trance states. Such shapes are universal and relate to background neural activity. The appearance of geometric shapes and dots may indicate any of the above activities and may help understand the human activity of geometry and building. Of particular interest would be dance or drug induced states of trance involved in shamanistic ritual activity proposed by many of those involved in palaeo-art studies.
Here's a link that might help.
http://dspace.dial.pipex.com/town/avenu ... toptic.htm
