Four classes of naturally rare vascular plant species are described and classified, based on parameters of spatial distribution and longevity. Properties intrinsic to these time/space parameters are explored and an importance hierarchy of causes of rarity is proposed for each class. These hierarchies serve as the basis for a predictive classification. Human causes of rarity such as habitat destruction and taxonomic difficulties are not considered in detail here but are discussed as confounding factors in the elucidation of rarity in vascular (...) plants. Several examples are provided to illustrate this classification and provide testable hypotheses concerning the origins of natural rarity in plant species. (shrink)

In his recent book on Darwinism, Daniel Dennett has offered up a species of a priori selectionism that he calls algorithmic. He used this view to challenge a number of positions advocated by Stephen J. Gould. I examine his algorithmic conception, review his unqualified enthusiasm for the a priori selectionist position, challenge Dennett's main metaphors (cranes vs. skyhooks and a design space), examine ways in which his position has lead him to misunderstand or misrepresent Gould (spandrels, exaptation, punctuated equilibrium, contingency (...) and disparity), and discuss recent results in developmental biology that suggest that an a priori position does not fill the demands of an evolutionary biology. I conclude by insisting that evolutionary biology is many leveled, complicated, and is carried on an ever shifting and expanding empirical base that when disregarded results in caricature. (shrink)