Ghost population

In genetic research, a "ghost population" refers to a population that has been inferred when analyzing genomes through the use of statistical techniques, yet which has not been adequately associated with a physical specimen.

Researchers may infer "ghost" populations when they identify sections of an individual's genome as displaying "excessively high sequence diversity" compared to the rest of their population, as such variation may reflect the individuals' inheritance of material ultimately sourced from members of "other", notably diverged lineages. However, "ghost" populations may not be so easily identified by contrast within a population when their inputs become common. Recently, a number of scholars have thus argued that analysis of population history can be improved by accounting for scenarios in which "ghost" populations have contributed similar material to various groups, as such analysis may disentangle various otherwise muddied relationships.

Importantly, the term "ghost population" is a functional term used in science and not a prescriptive one: populations are "ghosts" when they are inferred through scientific methods yet not identified with specific remains, and cease to be so if/when such remains are identified. For example, when Hall (2017) responded to Pagani et. al. (2016)'s claim that certain Oceanian populations had ancestry from an unknown "ghost" population, he noted that this ancestry was probably not "ghost" ancestry because it could reasonably be attributed to a branch of Denisovans.