Cytochrome b phylogeny and the taxonomy of great apes and mammals

In the Linnaean system of classification, the generic status of a species i s part of its binomial name, and it is therefore important that the classif ication at the level of genus is consistent at least in related groups of o rganisms. Using maximum-likelihood phylogenetic trees constructed from a la rge number of complete or nearly complete mammalian cytochrome b sequences, I show that the distributions of intrageneric and intergeneric distances d erived from these trees are clearly separated, which allows the limits for a more rational generic classification of mammals to be established. The an alysis of genetic distances among hominids in this context provides strong support for the inclusion of humans and chimpanzees in the same genus. It i s also of interest to decipher the main reasons for the possible biases in the mammalian classification. I found by correlation analysis that the clas sification of mammals of large body size tends to be oversplit, whereas tha t of small mammals has an excess of lumping, which may be a manifestation o f the larger difficulty in finding diagnostic characters in the classificat ion of small animals. In addition, and contrary to some previous observatio ns, there is no correlation between body size and rate of cytochrome b evol ution in mammals, which excludes the difference in evolutionary rates as th e cause of the observed body size taxonomic bias.