I have to take issue with your use of the term "evolutionary tree". It implies directionality to evolution, which leads so many people into the error of thinking that evolution is "pursuing perfection", as if evolution were an anthropomorphic personification with a particular goal in mind. It's the misconception that enables the silly argument about "Intelligent Design". Evolution pursues only local optimization, local both in time and space. Today's local perfection is tomorrow's deceased misfit.

You're absolutely right, of course. A more accurate comparison would be to some organism that spreads over a wide area in many directions from a single original source, but unfortunately "The Fungus of Evolution" just doesn't roll off the tongue very well.

When you extend this idea into the human noosphere, it becomes apparent that social and cultural diversity confers very much the same benefit. A culture is a body of ideas and beliefs which are more-or-less functional when measured against reality. When reality changes, ideas/beliefs that were advantageous may no longer be so beneficial, and another set of ideas and beliefs is selected to come to the fore as the most powerful way to think or act; the most adaptive, in other words.

This is also true, and I've thought a lot about the concept of cultural evolution, diversity, and value judgments on cultures. The parallels to physical evolution are many. This would almost be worth a whole thread by itself, but it isn't a coincidence that cultures that happily incorporate the best parts of many other cultures seem to be the most robust ones.