Abstract: Modern physics and biology satisfactorily explain the passage from the Big Bang to the formation of Earth and the first cells to present-day life, respectively. However, the origins of biochemical life still remain an open question. Any answer to the question must explain how an evolving ecology of polymers of ever-increasing length could come about on a planet that otherwise consisted only of small molecules. In this work, we use chemical reaction network theory to develop a formalism for defining a notion of ecology as well as different categories of evolution. We then construct abstract polymer models that can exhibit dynamics such that attractors in the polymer composition space with a higher average polymer length are also more probable. Furthermore, we demonstrate a polymerization model in two monomers that exhibits historical contingency. While this work provides a step forwards towards understanding the origins of biochemical life, we conclude with a discussion of the limitations of our formalism and directions where future work is needed.