Three roads diverged? Routes to phylogeographic inference.

Phylogeographic methods facilitate inference of the geographical history of genetic lineages. Recent examples explore human migration and the origins of viral pandemics. There is longstanding disagreement over the use and validity of certain phylogeographic inference methodologies. In this paper, we highlight three distinct frameworks for phylogeographic inference to give a taste of this disagreement. Each of the three approaches presents a different viewpoint on phylogeography, most fundamentally on how we view the relationship between the inferred history of a sample and the history of the population the sample is embedded in. Satisfactory resolution of this relationship between history of the tree and history of the population remains a challenge for all but the most trivial models of phylogeographic processes. Intriguingly, we believe that some recent methods that entirely avoid inference about the history of the population will eventually help to reach a resolution.