Bringing back extinct species could lead to biodiversity loss rather than gain, reports a paper published online this week in Nature Ecology & Evolution. The study suggests that further stretching already-strained conservation budgets to cover the costs of de-extinction could endanger extant species (species still in existence).

Joseph Bennett and colleagues performed a cost-benefit analysis to determine the number of species that governments in New Zealand (NZ) and the Australian state of New South Wales (NSW) can afford to conserve. They based their cost estimates on recently extinct species and similar extant species. They find that reintroducing some recently extinct species to their old habitats might improve existing biodiversity locally, but government-funded conservation for all 11 focal extinct species in NZ would sacrifice conservation for nearly three times as many (31) extant species. External funding for conservation of the five focal extinct NSW species could instead be used to conserve over eight times as many (42) extant species.

Although the technology for de-extinction is still some way off, the authors conclude that bringing back extinct organisms would require careful thought about what species to reintroduce, and where.