Frozen Evolution. Or, that’s not the way it is, Mr. Darwin. A Farewell to Selfish Gene.

Evolutionarily derived forms are termed apomorphic forms, abbreviated apomorphies. If several species (or higher taxa) within the studied phylogenetic line inherited certain apomorphies from their common ancestor, this apomorphy is termed a synapomorphy; in contrast an autapomorphy is an apomorphy that no other species shares with the given species. The distribution of synapomorphies within the given set of studied species is the best guide for reconstruction of cladogenesis. Even if two species share a large number of plesiomorphies, they need not be closely related in the particular line (Fig. XXIII.6). This could be only a consequence of the fact that the particular species did not change much during evolution, in contrast to other species, for example because it lives in the same environment as the common ancestor of the given line. In contrast, if two species share a large number of synapomorphies, this is most probably a result of the fact that they have a common ancestor that is simultaneously not the common ancestor of any of other studied species._s see Synapomorphies