thing is everywhere, arguing that the genetic evidence is revealing patterns in the microbial life of hotsprings and saltmarshes that are similar to those seen in the trees or birds in a forest. For example, places become less biologically similar the farther apart they are—which might seem obvious but is still contentious. The science, and debate around it, is only just getting under way. It may be that some view of life can bring bacteria and other microbes into line with other species, or it may be that microscopic life needs new rules. Either way, the possibility that we might have to junk our general theories should not dampen excitement about what biologists are discovering about the microbial world. Ecologists seeking generality have only one data point, the earth. This makes testing ideas difficult. But the microbial world gives us somewhere to test a century’s worth of theories built by ecologists who have studied plants and animals. It’s like having a whole other planet to play with.