Common ancestry is one of the pillars of Darwin’s theory of evolution. Today, the tree of life, which represents how all life is genealogically related, is often thought of as an essential component in the foundations of biological systematics and so therefore of evolutionary theory – and perhaps all of biology itself. It is an iconic representation in biology and even penetrates into popular culture.

Massive amounts of time, effort, and money are being put into understanding and reconstructing the tree. Yet there are serious debates as to the usefulness and even the very existence of the tree. Here I will attempt to critically evaluate the merits of some of these worries. In doing so, we will see that questions about the tree and the foundations of systematics can be answered in the light of a wide range not only of empirical considerations but of philosophical considerations as well. A historically informed picture of how and why we got to where we are today is important for understanding these debates; however, here I can give only the briefest of introductions to the history of the tree as it has been used in systematics before turning to contemporary and future considerations.