Perhaps it is awe-inspiring to evolutionary biologists to try to work a puzzle, trying to find how everything is connected by common ancestry.
Molecular clocks are a relatively simple concept.
Winston Ewert recently published a paper in BIO-Complexity suggesting that life is better explained by a dependency graph than by a phylogenetic tree.
One of the central pillars of the standard evolutionary model is the belief that all living species evolved from a common ancestor through a gradually unfolding tree of life.
The orderly pattern of biogeographic distribution of plants and animals was one of the lines of evidence that Charles Darwin mentioned in support of his theory.