The scale invariance in branch diameter dictates how much smaller a limb should be as it branches and how much investment a tree makes in a few thick branches versus many thin ones. Trees have evolved ...
Like the trees ... same tree that was a seedling when, say, King Tut was a boy. Now, if only King Tut and the rest of us brief-lived humans could have figured out a way to hang on so long.
The labels at the "tips" of a phylogeny can correspond to individual organisms, to species, or to sets of species, as long as each tip makes up a separate branch on the tree of life. In fact ...