I'm afraid I'm with Michael on this. That tree of life is an artifact of the visualization technique. It is only fractal in superficial ways. eg. Major branches are few, long and thick, whereas minor branches are many, short and thin. But those have no relevance - no counterpart - in the actual mechanic of evolution. They are an arbitrary human projection onto the diagram. If length of branch is mappable to time (what is length representing??), then there is no reason that some of the "narrowest twigs" in that diagram shouldn't be extremely twigs, whole others might be mere stubs. The appearance of thick=long and thin=short is, as above, an arbitrary human projection onto the diagram. The self-similarity, a hallmark of fractal processes, is imposed upon the visualization. IOW, we're making it look fractal, because it suits our aesthetics, not because the mechanics of evolutionary speciation actually dictate fractal growth.