Systematics and Macroevolutionary Hypotheses

Why we need to connect the study of genealogy to systematics. A genealogy connects the members of a set of individuals or taxa by a criterion of relationship by descent. Owing to extinction and to lack of preserval of many fossil species, any hypothetical genealogy is likely to lack many taxa and all we can hope to do is draw the relationships among the remainder. The object of systematics is to produce a classification of taxa; genealogy may be one of several criteria used to construct the classification, but our real classifications of various taxonomic groups are based on a mixture of criteria, unified only by a hierarchical structure. I will argue forcefully that any systematic scheme should be congruent to the genealogical relationships we can establish. I have to admit, however, that the acquisition of molecular data in recent years has caused the reports of genealogies to outstrip our capacity, and perhaps even our will, to incorporate them into systematic schemes.

The need to unify systematics with genealogy is very clear upon reading articles on diversity change in the fossil record. Systematics creeps into macroevolution because of the taxic approach to analysis, in which the comings and goings of taxa at given levels (e.g., family) are recorded as extinctions and appearances, which are converted to rates (e.g., Newell 1952; Sepkoski 1993). It is impractical to identify or record the comings and goings at the species level, so some higher taxonomic level is necessary as a surrogate (Sepkoski 1978, 1979, 1993).