they live in some places and not others. Other ecologists are working to find the general rules that might govern these patterns, in the hope that in a decade or two there will be a set of theories that can explain the patterns in nature. This begs the question of whether such theories could be linked into something even more general, something ecologists have already begun to explore. Drew Allen is combining metabolic theory and neutral theory to investigate the dynamics of evolution and extinction in foraminifera. Brian Enquist is teaming up with ecologists who study food webs and with those who study the patterns in how widespread and how common species are, to try and work out how size influences feeding behavior, and how animals use space. Steve Hubbell is working with physicists to incorporate energy into neutral ecology and to get a handle on species diversity in the process. Perhaps, he thinks, a metabolic view of mutation rates can help quantify the rate at which new species evolve, and provide a variable to plug into the formula for the universal biodiversity number. One day, Hubbell expects there to be a theoretical prediction of the number of species on Earth. Geoff West is dreaming of a grand unified theory of ecology that would bring all these ideas together, just as physicists seek links between quantum theory and relativity. Across the board, macroecologists are seeing where their ideas can take them, forming new collaborations, and creating a few antagonisms.
But we should also remember how little we know about nature. We have firm notions about how life works. It would be shocking—at least as momentous as finding extraterrestrial life—to discover a bacterium that did not use DNA to transmit genetic information or that had a genetic code radically different from the one humans use, or that didn’t use ATP as an all-purpose molecular fuel. It would be almost as surprising to find a mammal as small as a bee or an insect the size of a chicken. Yet we have almost no idea whether there are 5 million, 50 million, or 500 million species in the world. There are surprises to be had on even the best-known branches of the tree of life. The day I wrote this passage a new species of African monkey, the highland