ABSTRACT
A phylogeny is the set of genealogical relationships between species. There are many definitions of what a species is and how we should recognize species (Mayden, 1999). Nevertheless, there is general agreement among the differing species concepts that a species will be made up of a lineage of populations that are connected by ancestor-descendant relationships between the individuals. Significantly, different species do not represent independent samples from some pool of possible species. Rather, species typically arise by a process of diversification in which one ancestral species splits to form two or more descendant species. Hybridization between existing species is another speciation mechanism (see Mallet, 2007, for a recent review). In either case, different species can be classified based on how closely they are related – how far back in time one must go to find their common ancestor.
