A Macromolecular Perspective on The Material Basis of Evolution

Abstract

Comparisons of homologous proteins and nucleic acids in extant organisms allow us a routine and relatively objective access to much of an evolutionary picture previously clouded or utterly unknown. This increased clarity applies as much to the evolutionary processes involved as to the phylogenetic framework linking those organisms and, by implication, their fossilized progenitors. The particular virtues of the molecular comparative approach are several. First, the comparative material is ubiquitous — the homologous molecules are always present for any necessary comparison, and homologies are only rarely in question. Next, the unit of change, an amino acid or nucleotide substitution, is known. Third, the pattern of change is known — protein and nucleic acid evolution produce, in the main, differentiation. Finally, one need not have specialized knowledge of a particular group to work out its phylogeny — the various techniques available are rather routinely applicable. It then follows that the differences among modern organisms are measurable along a common scale in the same units and are patently derived characters. Thus, one is able to, in large part, simply to count the amino acid or nucleotide sequence differences among extant species and apportion them along a unique, derived phylogeny linking those species.