THE HAZARDS OF LIVING ON A SINGLE PLANET: What zoonotic diseases are, and how to stop them. “New human pathogens arise in two ways. They may evolve from old ones, or they may jump to humanity from other species. The second is the more common route. Infections that jump in this way are called zoonotic diseases, or zoonoses. This seems to have been the route taken by Ebola fever, the latest outbreak of which has claimed more than 10,000 lives. . . . Zoonoses are particularly likely to develop when people and animals live in close proximity to each other. One reason southern China often spawns them (SARS was not unique; a lot of influenza begins there, too) is that the region has a plethora of small farms, in which many species of animal live in close quarters with each other and with human beings. The constant crossing of pathogens between the species involved makes it more likely that one will emerge that can thrive in people.”