'Type' in morphology and phylogeny.

Comparative morphologists, developmental biologists, as well as paleontologists, recognize the existence of 'types,' or 'Baupläne,' in nature, marked out by a certain 'sameness' of structure that prevails through all variation in shape and function. The 'sameness' that marks out 'types' is one of structural correspondence (topology and connectivity), which is believed to be causally rooted in ontogeny (developmental constraints). In an evolutionary context, the structural relations that mark out 'types' are explained as relations of homology. The use of concepts such as 'type' or 'Bauplan' has been criticized from a 'populational thinking' point of view as being incompatible with current evolutionary theory. The present article explores the contrasting viewpoints, and concludes that current evolutionary theory can accommodate the concept of a 'type' in the sense of a 'homeostatic property cluster natural kind.' The 'homeostatic property cluster natural kind' is a nonessentialistic concept that allows the kind to be historically delimited. Copyright 2006 Wiley-Liss, Inc.