Expertise is an intensely practical term, in that it's the ability to accurately apply appropriate knowledge. As such it is relative and therefore reliant on context for meaning. The problem is that the context is changing so fast that expertise has a very limited shelf-life. The accurate application of appropriate knowledge defines an Expert as opposed to a Practitioner. Previously, when it was knowledge and not expertise that was limited, Experts climbed further to the end of each branch of learning, and were acclaimed when they discovered a new bifurcation in their area of the tree. The tree is now growing so quickly that this kind of expertise is being buried by an avalanche of discovery. New kinds of what I would call "Meta-Experts" are needed -- those who cross-branch learning and bring it back into circulation. Perhaps we need a different model. Instead of a Tree, why not a circulatory-system? Mainstream, Institutional learning could be likened to the arterial-side and the novel, opportunistic expertise that returns it for general circulation, the venous side. Each depends on the other for social-progress, although often neither are prepared to admit it.