Uses for evolutionary trees

The general impression of molecular evolution is often that one sequences a gene from a number of organisms and infers the evolutionary relations of the organisms. Indeed, if the sequences turn out to be orthologous and the data robust, one will get a phylogeny (tree) depicting those historical relations. But what one really obtains is a gene tree (I shall henceforth assume that the data are robust; that is another problem) and the biological messages implicit in that tree can be quite various. This article lists a number of those messages that one may have or may wish to look for.