The idea of a species - How do we define species?
The phenetic species concept
Species are in practice recognized by taxonomists by their phenotypic characters. This has been extended to the phenetic species concept in which the pheneticist then says that species are groups of individuals with certain morphological characters. What defines the bird opposite as a golden eagle is simply the fact that it conforms to the phenetic description of a golden eagle.
However, for the evolutionary biologist this is inadequate. When species are identified phenetically, it is only for practical convenience and the underlying theoretical concept of species is something other than a phenetic cluster.
For the theorist, a successful species concept should satisfy these conditions:
• Whether they make internal theoretical sense: that is, whether they identify a fundamental unit in evolutionary theory.
• Whether they explain the existence of phenetic clusters in nature.
In this tutorial we will examine different species concepts and see how well they meet these criteria.