Internal evolutionary conflicts: a conceptual synthesis and mathematical primer

Internal evolutionary conflicts arise when elements within an organism have diverging fitness interests. Examples range from meiotic drive and cytoplasmic male sterility to transposable elements and supernumerary B chromosomes. While once treated as genetic curiosities, they are now seen as widespread and major drivers of eukaryotic genome evolution. Yet their study remains fragmented, with no clear entry point not only for those who wish to gain an overview of theoretical advances, or those who wish to construct models of their own. Here, we discuss ways in which internal evolutionary conflicts have been modelled and develop a common population genetic framework for building such models. The framework provides explicit criteria for what counts as conflict, distinguishing it from fitness trade-offs, and formalises how and when internal conflicts arise. By treating different cases within the same structure, it shows that these diverse phenomena share a common logic.