Schematic of coalescence. Lines connect individuals with their ancestors, with each generation a horizontal array of individuals (e.g., ). Time advances going up the page; hence, the parent of an individual is in the line below (e.g., is the parent of ). The coalescent is indicated with thick lines. Individuals and are in the coalescent; is not in the coalescent but is descended from the MRCA of the coalescent; is not in the coalescent and is not descended from the MRCA of the coalescent.
