Modern classification, based on phylogeny, no longer places humans at the center of nature. Groups of organisms are no longer defined by their general appearance, but by their different individual characteristics. Phylogeny, therefore, by showing common ancestry, outlines a tree of evolutionary relationships from which one can retrace the history of life. This book diagrams the tree of life according to the most recent methods of classification. Each branch of the tree is a group that includes the hypothetical ancestor and all its descendants. The basis for classification is the evolutionary adaptations that the unique ancestor passed to its modern-day descendants.