Ancestral Areas: A Cladistic Reinterpretation of the Center of Origin Concept

Abstract

The search for centers of origin has fallen into disrepute because of unfounded assumptions and spurious criteria. Nevertheless, a proper approach to understanding ancestral areas would enhance the study of the natural history of organisms. If there is reason to assume that a group originally had a more restricted distribution than it has today, a method for estimating that ancestral distribution is warranted. I describe a cladistic procedure for approximating ancestral areas of individual groups from the topological information in their area cladograms. Each area is treated as a single character, which may be optimized onto the cladogram using either forward or reverse Camin-Sokal parsimony. By comparing the numbers of necessary gains and losses under the two optimizations, respectively, it is possible to estimate which areas were most likely parts of the ancestral area. By applying the method to a cladogram of the globally distributed angiosperm family Asteraceae, I estimated that the ancestral area involved both South America and the Pacific. Application to recently published cladograms of human mitochondrial DNA provides an objective evaluation of the support for any particular geographic origin of humans.