WAGNER, G P: What are morphological characters and how may they originate?

From an organismal point of view the increase in apparent complexity of organisms is correlated or may even be defined as the increase in the number of individualized body parts. Hence, from this point of view, the increase in metazoan complexity is synonymous with the origin of new characters. In order to understand the origin of new characters we need to establish what apomorphic developmental features are necessary to obtain a new character. Based on a comparison of examples from vertebrate evolution I propose that the origin of a new character requires one of the three following types of evolutionary events: 1) the origin of a new developmentally individualized body part, or 2) the transformation of an existing body part to acquire a new set of constraints or variational opportunities, or 3) the integration of ancestrally independent characters into a new unit. For the first kind or transformation the origin of the tetrapod autopodium will be discussed. In particular I will focus on recent work on what kind of genetic changes might be involved in the origin of the tetrapod limb. For the second kind, the origin of feathers as proposed by Richard Prum will be discussed.