Cancer is in fact a biological phenomenon that appeared more than half a billion years ago and has persisted through the evolution of many organisms, including the human species. And that changes everything. Our oldest enemy is governed by the same rules that govern all living systems. Thus it is in the light of evolutionary biology that we need to reconsider our approach. Thanks to a 150-year-old theory -- that of Darwin, to be exact –we are finally beginning to understand the logic of cancer and can hope one day to stop it.