The main departure is looking at how lanaguages actually stymie the flow of ideas. With a greater disversity of languages in more densely populated regions of the world, their number ringfence idea pools, preserving group's competitive advantage (or so he muses). These differences even reduce the flow of genetic information. This phenomena is an interesting counter reaction to the potentially homognising force of horizontal idea transfer.
Clearly, an situation like this can be thought to have evolved as much for it's widespread benefits, as for any short-term, local, competitive advantages. Just like the evolution of cellular life created myriad parallel laboratories for evolving better genes (through speciation), all these weakly connected cultural domains forster diversity. This is essential to avoid the entire population getting stuck down dead end paths, local optima that are impossible to back-track from. Diversity is the truly dominant evolutionary force (not refinement!), and it applies even more so to memetics, as with genetics.