TREE OF LIFE

A metaphor describing the interrelationships of all life on Earth in the context of evolution. However, the concept of the tree of life has been used in science, religion, philosophy and mythology. The tree of life illustrates the idea that all life forms branched out from a common ancestor and aids the understanding of evolution. Charles Darwin is attributed with having produced one of the first evolutionary trees of life in AD 1859, although several trees had previously been produced. These early trees only focused on part of life; for example, the first tree published [Page 1112]in 1801 by Augustin Augier showed the relationship between members of the plant kingdom. Jean-Baptiste Lamarck produced the first branching tree of animals in 1809, but he did not believe in a common descent of all life and thought that life consisted of separate parallel lines advancing from simple to more complex forms. In 1840, Edward Hitchcock published the first tree of life based on palaeontology but he had separate branches for plants and animals and they both began with multiple origins. The year before Darwin published his tree of life, Heinrich Bronn proposed a hypothetical tree of life with a single origin but did not propose a mechanism of change. Since Darwin’s tree of life was published, there has been plenty of evidence to support the theory of evolution by natural selection, and genetics has confirmed that all life on Earth had a common ancestor.

The concept of a tree of life is simplistic, and modern evolutionary trees exclude the assumption that evolution progresses from primitive to developed, with the anatomically modern humans (AMH) at the top. While a model of a tree is still considered valid for eukaryotic life forms, prokaryotes (archaea and bacteria) have the ability to transfer genetic information between unrelated organisms through horizontal gene transfer by processes such as recombination, gene loss, duplication and gene creation, which causes variation that is not due to vertical transfer. The modern view is that evolution is much more complex; modern trees of life are called phylogenetic trees, which show the inferred evolutionary relationships among various biological species based upon similarities and differences in their physical and/or genetic characteristics.