Guest Author - Catherine Ebey
The history of phylogenetics is long and complex. Several scientists created tree diagrams that illustrated the relatedness of organisms but did not use evolutionary, heritable characteristics to form their trees based on hypothetical common ancestors. After Charles Darwin proposed his theory of evolution phylogenetic trees flourished in their true forms based on heritable characteristics.
In 1801 French botanist Augustin Augier created a tree of life he called “Arbre Botanique.” This drawing detailed the relationships among plants. His tree of life was very detailed and contained different members of the plant kingdom assigned to the trunk of the tree, larger limbs, shoots and leaves.
It seems fitting that a botanist should create the first recognized phylogenetic tree, since botanists are the boldest supporters of abandoning classic taxonomy and exclusively embracing phylogenetics.
Jean-Baptiste Lamarck created a tree of life diagram that showed evolutionary relationships among animals. His tree of life was the first to illustrate heritable traits, although other aspects of his theory were later disproved by Darwin. Unlike those who had come before him, he based his tree on the connections between ancestors and descendants.
Robert Chambers studied fossil evidence in the mid-1800s. In 1844 Robert Chambers published a very simple phylogenetic diagram in his work Vestiges of the Natural History of Creation that illustrated the connections between reptiles, birds, fish and mammals.
Heinrich-Georg Bronn also constructed a tree in his work on paleontology. His work is seen as the prototype of Darwin’s tree. However, Darwin’s tree was the first to illustrate evolutionary relationships. All other precursor trees described merely used a tree to organize other biological information. Darwin’s tree was the first tree to show evolutionary relationships from a hypothetical common ancestor.
In 1872, Charles Darwin published his famous book, The Origin of Species. Darwin postulated that species evolve through natural selection. The process of natural selection enables divergence of characteristics through hereditary inheritance.
Darwin included a diagram of a basic phylogenetic tree in his book that detailed his vision of nested species and their relationships to other species. This important beginning of the theory of phylogenetics is marked by the fact that this was the only diagram Darwin included in his most famous work.
In his book, Darwin details his vision of the “great tree of life” as a pictorial metaphor for the interrelatedness of species through their ancestors and their descendents. He relates the fractal nature of the different genera, families, subfamilies and species through the branching of trees. He describes how the previously formed branches of the tree are like the extinct species that are now overshadowed by the flourishing, green shoots of new growth. These green shoots represent the new species that have evolved through natural selection for characteristics that have allowed them to overtake their ancestors.
Ernst Haeckel (1834-1919) read Darwin’s work. He supported Darwin’s theory of evolution and the use of a phylogenetic diagram or an evolutionary tree. He made several of his own phylogenetic diagrams in his investigations of single-celled organisms and human descent.
Haeckel believed that he could trace the human line through the evolutionary tree of life to the lowest life forms, which he believed were single-celled organisms (we know today these single-celled organisms—bacteria—do in fact exist. He went to great lengths to diagram evolutionary histories to illustrate his two hypotheses. He formulated a theory known as gastraea in which he endeavored to trace all multicellular organisms back to a hypothetical common ancestor.
His tree of life diagrams were highly stylized. They look quite different from the simple diagrams we use today. He went so far as to draw the fictional tree in great detail with leaves, branches and a tree trunk that were all realistically shaded with a pencil.
German zoologist Willi Hennig built on Darwin’s theory of evolution with his own theory of cladistics. In 1950 he published his ideas in German. His work was later translated into English under the name Phylogenetic Systematics. He proposed how to methodically construct phylogenies using hypothetical common ancestors, sister clades and inherited traits. According to the Willi Hennig Society, he grouped species together based on synapomorphies (shared and derived features of organisms). These similar characteristics are also known as homologues.
Willi Hennig created the basis of modern phylogenetic trees. We still use his methodologies in creating these phylogenetic tree diagrams today. Phylogenetic trees are widely used in biology to place organisms within their evolutionary and biological history. The more we learn about interspecies relationships, the easier it is to construct a complete evolutionary history of all organisms on earth.