But we know for certain that this back-to-the-water evolution ... these animals is necessarily a direct ancestor of the whales we know today; they may be side branches of the family tree.

A new book details how lignin once protected algae from UV radiation, then later in evolutionary time became a structural support for trees.

Evolutionary trees show how different species have evolved ... So the question is, why? How could an animal be so precisely adapted to a particular lifestyle? The answer is natural selection.