After decades of debates about species concepts, there is broad agreement that species are evolving lineages. However, species classification is still in a state of disorder: different methods of delimitation lead to competing outcomes for the same organisms, and the groups recognised as species are of widely different kinds. This paper considers whether this problem can be resolved by developing a unitary scale for evolutionary independence. Such a scale would show clearly when groups are comparable and allow taxonomists to choose (...) a conventional threshold of independence for species status. Existing measurement approaches to species delimitation are typically shot down by what I call the heterogeneity objection, according to which independently evolving groups are too heterogeneous to be captured by a single scale. I draw a parallel with the measurement of temperature to argue that this objection does not provide sufficient reasons to abandon the measurement approach, and that such an approach may even help to make the vague notion of evolutionary independence more precise. (shrink)

The relation between conservation science and taxonomy is typically seen as a simple dependency of the former on the latter. This dependency is assumed to be strictly one-way to avoid normative concerns from conservation science inappropriately affecting the descriptive discipline of taxonomy. In this paper, I argue against this widely assumed standard view on the relation between these two disciplines by highlighting two important roles for conservation scientists in scientific decisions that are part of the internal stages of taxonomy. I (...) show that these roles imply that the two disciplines should be interdependent and that value-judgments should play a substantial role in both. (shrink)