Phylogenies And Quantitative Characters

Abstract

Systematists and evolutionary geneticists don't often talk to each other, and they routinely dispaiage each other's work as being of little relevance to evolution. Systematists sometimes invoke the punctuationist argument that most evolutionary change does not occur by individual selection and hence that within-population phenomena are largely irrelevant to evolution. They sometimes make the pattern-cladist contention that evolutionary processes cannot be inferred from any observation about pattern, nor can any knowledge of evolutionary processes inform inferences about pattern. More frequently systematists feel, with considerable justification, that evolutionary geneticists have simply failed to concern themselves with morphological characters and data on differences between species. Evolutionary geneticists in turn dismiss the idea that studies comparing species anciently diverged, using morphological characters far removed from the level of the gene and using nonquantitative methods, can either be sound in their inferences of pattern or can shed much light on evolutionary processes. Changes in the methods of collecting and analyzing data are invalidating some of these views. Molecular data, such as nucleic acid sequences, give us observations at the gene level that are comparable across many species, and consideration of these data has drawn population geneticists across the species boundary. The availability of microcomputers and digitizers is leading to more quantitation of morphological data by systematists, and the field of