| A cladistic taxonomy represents a distinct approach to trait categorization insofar as trait categories are determined not by morphological or functional features, but by historical relations. This essay attempts to articulate the contents of a cladistic system for categorizing organismic traits.; Under a cladistic taxonomy, trait categories should be conceived as delimited historical lineages of traits where all members of the category are homologues of one another. I argue, moreover, that the analysis of 'homology' necessary for individuating homologous traits, and in turn cladistic categories of traits, is one that features in the genetic basis of development for those traits. Specifically, evolutionary conserved developmental pathways represent a means by which homologous traits can be distinguished from one another.; Importantly, this analysis of homology also accommodates the hierarchical nature of a cladistic system. A successful taxonomy of traits must provide for the possibility of both wide and narrow trait categories. On this view, a wide category will be one that is more evolutionarily divergent and narrow categories will be more evolutionarily proximate. I emphasize here the fact that developmental pathways preserve genetic elements across evolutionary time, and that wide cladistic categories will share a limited set of elements found in a historical line of developmental pathways, while a narrow cladistic category will show greater similarity in the numbers of elements.; Once fully characterized, I evaluate a cladistic taxonomy's place within the biological sciences. I examine, in particular, whether the success of a cladistic taxonomy of traits should motivate the displacement of functional categories, gesturing intermittently to the role of morphological categories as well. I show first that cladistic categories will often prove more useful for many discipline specific projects in biology. But despite these advantages of a cladistic taxonomy, I maintain cladistic categories should not displace functional classification, since only functional categories will be appropriate in disciplines such as ecology. I advocate, therefore, a pluralist view of trait categorization in biology. |
