Introduction

Darwin was obsessed with origins. The book with which he distinguished himself as among the greatest thinkers ever to have walked on Earth, The Origin of Species by Means of Natural Selection or, The Preservation of Favoured Races in the Struggle for Life, was intended as only an abstract to a ‘big species book’ (Gould, 2002) about organisms and their environments and how they interact to elicit change over time. In a letter to Hooker (Darwin, 1871), Darwin speculated on how life, itself, might have originated, including the now infamous notion that it started in a ‘warm little pond’. As Einstein would do for physics with space and time less than a half-century later (Minkowski, 1952), Darwin, in his magnum opus and personal correspondence, accomplished for biology: ecology and evolution were inextricably linked forevermore.

But origins posed problems for Darwin, even concerning particular groups, such as metazoans (i.e., animals): ‘[t]here is another and allied difficulty, which is much graver. I allude to the manner in which numbers of species of the same group, suddenly appear in the lowest known fossiliferous rocks’ (Darwin, 1859; in the section titled ‘On the Imperfection of the Geological Record’).

In this chapter, we consider the origin of metazoans as a model for the origin of life. Considering only a group within the tree of life offers us three advantages in demonstrating our thesis (which is described in the subsequent paragraph).