WOULD the animal have made it into the ark? That’s the kind of question conservationists have been asking when it comes to the thorny issue of picking which threatened species to save.

Kerstin Zander of the Charles Darwin University in Darwin, Australia, and her colleagues looked at conserving cattle – the species with the most number of breeds to have gone extinct. They turned to an approach first outlined by economist Martin Weitzman at Harvard University.

In the 1990s, Weitzman devised a formula for prioritising species for conservation. This considers the cost of saving a species, how useful or genetically …