The affinities of all beings in the same class have sometimes been represented by a great tree.
I believe this simile largely speaks the truth. The green and budding twigs may represent existing species, and those produced during each former year may represent the long succession of extinct species. The limbs divided into great branches, and these into lesser and lesser branches, were themselves once budding twigs. This connection of the former and present buds by ramifying branches may well represent the classification of all extinct and living species in groups subordinate to groups.
From the first growth of the tree, many limbs and branches have decayed and dropped off. These lost branches, of various sizes, may represent whole orders, families, and genera that have no living representatives. They are known to us only from having been found in a fossil state. As buds give rise to fresh buds through growth, and these buds, if vigorous, branch out and overtop all feebler branches, so I believe it has been with the Tree of Life. It fills with its dead and broken branches the crust of the earth and covers the surface with its ever-branching and beautiful ramifications” (Darwin, 1859). Bibliography: The theory of evolution, formalized by Charles Darwin, is as much a theory as the theory of gravity or the theory of relativity.
Unlike theories of physics, biological theories, and especially evolution, have been argued long and hard in socio-political arenas. Even today, evolution is not often taught in primary schools. However, evolution is the binding force of all biological research. It is the unifying theme. In paleontology, evolution gives workers a powerful way to organize the remains of past life and better understand the one history of life.
The history of thought about evolution, in general, and paleontological contributions specifically, are often useful to today’s workers. Science, like any iterative process, draws heavily from its history.