Of course we want to save the panda. Pandas are cuddly, furry and charismatic, and even cuter when they sneeze. But a new approach to conservation policy suggests that we ought to be prioritising our efforts in a different way. The Evolutionarily Distinct and Globally Endangered (EDGE) index aims to measure how "evolutionarily distinct" (ED) a given species is, with the idea that more evolutionarily distinct species are more worth preserving.

Conservation is, on the whole, a worthwhile aim; let us take that as read. But, in a world where thousands of species are in imminent danger of extinction, how should we focus our efforts? Certainly it may be useful to develop metrics such as the EDGE index to help us assess how we should prioritise in making decisions about which species to save. Without an account of what it is we value about biological species and why, however, these numbers are meaningless; we might as well be measuring size, or colourfulness, or some other arbitrary trait.

So, why is evolutionary distinctness valuable? There are of course many possible answers to this question: the 'weirdness' of a species may correlate with its significance within an ecosystem, its potential uniqueness, its value to science and related applications. The point stands, though, that we need to be aware of where this value lies, if we are to base our actions upon it. In setting conservation policy we need to define what we consider to be valuable and why, and understand how the statistics presented to us reflect this.