 However, one unanticipated consequence of such a proliferation of data and trees has been the repeated finding that many prokaryotic organisms exchange genes between lineages, including genes of major lineage-defining importance. The extent and significance of such transfers is such that the standard method of constructing a phylogeny, in the form of a graph-theoretic representation of lineages admitting only vertical descent, is violated. In addition, molecular data reveals the extent of hybridization in multicellular organisms (Mallet et al. 2016). The tree of life therefore becomes a questionable construct (Doolittle &amp; Bapteste 2007; Dagan &amp; Martin 2009), both metaphysically and pragmatically. At the very least, any philosopher reflecting on the tree of life and what it represents will have to consider microbial evolution (Velasco 2010).