Darwin's Theory of Descent with Modification, versus the Biblical Tree of Life

There is a strong urban myth that Charles Darwin introduced and/or advocated a ‘‘Tree of Life’’ for the classification of living organisms. This has recently been highlighted by Lawton [1], but dates back to at least Doolittle [2]. It is often combined with the idea that we require a ‘‘paradigm shift’’ to take into account extensive lateral gene transfer, especially in prokaryotes. Yes, extensive lateral gene transfer occurs widely in prokaryotes (see [3–5]), and this enriches our understanding of evolution by emphasizing a more gene-centered view. In contrast, though acknowledging the prior availability of the tree of life simile, Darwin continually referred to his ‘‘theory of descent with modification’’, an expression that encompasses a wide variety of fundamental processes including both vertical descent and lateral gene transfer, thus removing any need for paradigm shifts. For Western Europe, the Tree of Life phrase is biblical in origin and, although in Darwin’s words, it is ‘‘a useful simile’’, it is best not interpreted literally. The basic confusion may have arisen because it is not recognised that Darwin was mainly interested in the mechanisms of evolution. These include both whether mechanisms that could be studied in the present could explain past events, and establishing the continuity between all living creatures. He was not primarily interested in the description of the patterns of evolution. We need to reappraise the different concepts, what Darwin meant by them, and how he used the terms. The Tree of Life example is not the only case where Darwin’s work has potentially been misunderstood (and I will mention some of these later). In contrast to being interested in describing patterns of relationships, I argue that Darwin appears to have been more interested in the extent to which mechanisms that can be studied in the present are both necessary, and sufficient, to explain events in the past—an approach that I interpret as being learned from his geological background (Figure 1) [6,7].