It is a natural human impulse to think of evolution as a long chain of improvements, of a never-ending advance towards largeness and complexity - in a word, towards us. We flatter ourselves. Most of the real diversity in evolution has been small-scale. We large things are just flukes - an interesting side branch. Of the twenty-three main divisions of life, only three - plants, animals and fungi - are large enough to be seen by the human eye33, and even they contain species that are microscopic. Indeed, according to Woese, if you totalled up all the biomass of the planet - every living thing, plants included - microbes would account for at least 80 per cent of all there is34, perhaps more. The world belongs to the very small - and it has done for a very long time.