A world of categones devmd of spirit waits for life to return. Saul
Bellow, Humboldt's Gift The stock-in-trade of communicating hypotheses
about the historical path of evolution is a graphical representation
called a phylogenetic tree. In most such graphics, pairs of branches
diverge from other branches, successively marching across abstract time
toward the present. To each branch is tied a tag with a name, a
binominal symbol that functions as does the name given to an individual
human being. On phylogenetic trees the names symbolize species. What
exactly do these names signify? What kind of information is communicated
when we claim to have knowledge of the following types? "Tetonius
mathewzi was ancestral to Pseudotetonius ambiguus. " "The sample of
fossils attributed to Homo habzlis is too variable to contain only one
species. " "Interbreeding populations of savanna baboons all belong to
Papio anubis. " "Hylobates lar and H. pileatus interbreed in zones of
geographic overlap. " While there is nearly universal agreement that the
notion of the speczes is fundamental to our understanding of how
evolution works, there is a very wide range of opinion on the conceptual
content and meaning of such particular statements regarding species.
This is because, oddly enough, evolutionary biolo- gists are quite far
from agreement on what a species is, how it attains this status, and
what role it plays in evolution over the long term.