[exschke]

Well yes, the idea of shrinking brains is not that simple to explain. We want to believe that we're smart because we have to deal with louds of information, solve complex problems and other bla-bla-bla.
But perhaps it is true that humanity is very narrow minded in its development. Perhaps we miss some important spheres of growth. I.e., spiritual develpment, with all that it can entail. Somehow people always want to believe that humanity develops from simple to more complex. It could be that Cro-Magnons were experienced in shamanistic practices and could achieve things that we never even dream of now...
For instance, some research say that meditation can increase in brain size... http://www.physorg.com/news10312.html