Potential scenarios for genetic patterns of differentiation detected after admixture between two diverged lineages. FST is calculated between two populations before (grey) and after admixture (black) for a large number of loci. As a result of the admixture, the current mean differentiation is reduced compared to the historical mean by an amount ΔMFST. The FST observed at individual loci will also change but the difference between the current and the historical value (ΔLFST) will depend on the selection regimes before and after admixture. Note that filled circles indicate loci under divergent selection, and empty circles indicate loci evolving neutrally at a given point in time. In a genome scan carried out today (i.e. after admixture), a locus would fall within the tail of the current FST distribution (black shaded area) and be considered an outlier under one of the following scenarios: a) On-going selection before and after admixture. b) Novel selection only after admixture. c) Past selection only before admixture, representing the ‘ghost of selection past’. Under scenario “c”, the outlier status of the locus will be transient.