The simultaneous mapping of DNA mutations and epigenetic changes as colorectal cancer evolves has for the first time tracked their relative contributions and shown epigenetic control of gene transcription is far more important than somatic mutations in enabling tumors to adapt and develop a survival advantage over other cells. In an analysis of 1,373 samples from 30 colorectal cancer samples, epigenetic changes were highly common in cells that had become cancerous and occurred around known cancer driver mutations. These epigenetic alterations were heritable, were passed on at each cell division, and in addition to a direct contribution to the evolution of tumors also influenced how cancer cells accumulated DNA mutations. The modifications to gene regulation conferred survival advantages that meant cancer cells grew faster than normal counterparts. While it is not news that epigenetic changes are involved in tumor development, previously it was not clear what the relative contribution was, and that their effect could be independent of DNA mutations.