Depicting the Tree of Life: the Philosophical and Historical Roots of Evolutionary Tree Diagrams

Abstract

It is a popularly held view that Darwin was the first author to draw a phylogenetic tree diagram. However, as is the case with most popular beliefs, this one also does not hold true. Firstly, Darwin never called his diagram of common descent a tree. Secondly, even before Darwin, tree diagrams were used by a variety of philosophical, religious, and secular scholars to depict phenomena such as "logical relationships," "affiliations," "genealogical descent," "affinity," and "historical relatedness" between the elements portrayed on the tree. Moreover, historically, tree diagrams themselves can be grouped into a larger class of diagrams that were drawn to depict natural and/or divine order in the world. In this paper, we trace the historical roots and cultural meanings of these tree diagrams. It will be demonstrated that tree diagrams as we know them are the outgrowth of ancient philosophical attempts to find the "true order" of the world, and to map the world "as it is" (ontologically), according to its true essence. This philosophical idea would begin a fascinating journey throughout Western European history. It lies at the foundation of the famous "scala naturae," as well as religious and secular genealogical thinking, especially in regard to divine, familial (kinship), and linguistic pedigrees that were often depicted by tree images. These scala naturae would fuse with genealogical, pedigree thinking, and the trees that were the result of this blend would, from the nineteenth century onward, also include the element of time. The recognition of time would eventually lead to the recognition of evolution as a fact of nature, and subsequently, tree iconographies would come to represent exclusively the evolutionary descent of species.

Categorizing Ideas about Trees: A Tree of Trees

“…After all, the botanist Augustin Augier (1801) provides compelling evidence: he used such a “tree” that way –obviously in a non-computerized manner- in a non-transformist theory of life. And outside science, trees had been used for long ago to organize the world in a hierarchical manner without any evolutionary connotations [9].…”

“…Also, we limited the sampling to the modern scientific era. Trees used to support metaphysical views beyond science before the XVII th century (see [9] are out of the scope of the present analysis. In the same way, we chose to limit ourselves to Natural History: we study trees depicting the diversity of life, not trees organizing knowledge (e.g.…”

Historical and Epistemological Perspectives on What Horizontal Gene Transfer Mechanisms Contribute to Our Understanding of Evolution

“…For one, trees are the number one icon for many world religions, and they were also used in pre-evolutionary societies to depict non-evolutionary, abstract and logical, or genealogical descent relations of divine and earthly phenomena. Debunking tree images therefore hardly feeds into creationist thought (Gontier 2011). Secondly, reticulate evolution can be proven by an enormous amount of data, and these theories in no way lend credibility to the ideas of creationism.…”

“…Darwin pondered about these questions in his Notebook B that he filled in 1837-38. Inspired by familial pedigree thinking and genealogical tree models that illustrate the natural history of languages (Gontier 2011), on the one hand, Darwin favored a "tree of life metaphor" because species do not "really pass into each other." On the other hand, he wondered whether "The tree of life should perhaps be called the coral of life, base of branches dead; so that passages cannot be seen," but he added that such an imagery "offers contradiction to constant succession of germs in progress" and "makes it excessively complicated" (Darwin 1837(Darwin /1838.…”

Reticulate Evolution

“…Inspired by familial pedigree thinking and genealogical tree models that illustrate the natural history of languages (Gontier 2011), on the one hand, Darwin favored a "tree of life metaphor" because species do not "really pass into each other." These non-evolutionary genealogical tree diagrams were later adopted by Charles Darwin and Ernst Haeckel to understand and depict evolutionary descent relationships of biological species.…”