outweigh those of “land-sparing” (farming intensively on a smaller area). A couple of recent papers—a theoretical one by David Tilman of the University of Minnesota and an empirical study by Ben Phalan of Cambridge University, looking at data from Ghana and India—suggest that land-sparing wins. Richer countries tend to be better informed about the value of ecosystems and take a longer view. That is why China, having destroyed so much of its forest, is now paying its farmers to plant trees. The ecological value of some of the resulting forest is open to doubt—a lot of it is monoculture of imported varieties that do not always suit the local climate—but the numbers are impressive. Forest cover increased by a third between 1990 and 2010. Better-off countries also have more effective governments, without which conservation would be impossible. Elephants are doing better in southern Africa than in East or Central Africa. South Africa, Zimbabwe and Botswana all have well-administered parks and reasonably effective police forces; in Congo, Chad and Tanzania, those institutions are shakier. Richer countries are generally more peaceful, too. That is good for their people, but notalways for other species. Biodiversity sometimes benefits from conflict: where it keeps people out, it may conserve habitats for other creatures. The 1,000-sq-km demilitarised zone between North and South Korea, for instance, has become a de facto nature reserveof great interest to scientists. On balance, though, conflict tends to do more harm than good to biodiversity, destroyinghabitats and undermining states’ efforts to protect other creatures. That is another reason why elephants are doing better in southern Africa than in Central and East Africa, where militias have plenty of guns and a financial interest in selling ivory to fund their wars. The impact of prosperity on human demography also benefits biodiversity, but it takes time. In its early stages economic growth often causes people to multiply faster as death rates come down but birth rates stay high, as is happening in Africa now. That intensifies competition for resources between humans and other species. But when countries become richer, more women get educated and take jobs, more people move away from farms and into cities and birth rates start falling. In East Asia fertility has fallen from 5.3 children per woman in the 1960s to 1.6 now. In some countries—Japan, Russia, much of eastern Europe and some of western Europe—the population is already declining. But in Africa it is still rising fast, which is the main reason why the UN expects the world’s population to continue expanding to the end of this century. Lastly, growth brings scientific advance, which makes it easier to mitigate threats to biodiversity. So far conservation has been dominated by men in shorts with not much more than a pair of binoculars. Now the digital revolution is transforming it.