A controversial article published in the PNAS suggests that zoos should manage animal populations through culling rather than contraception to ensure species survival. Researchers, including Markus Klaus from the University of Zurich and others, argue that current contraceptive methods threaten reproductive capabilities and that euthanasia might be a necessary measure for the long-term health of zoo populations. They highlight the diminishing breeding numbers of species like giraffes and stress the importance of maintaining active breeding rather than just a collection of aging animals.