It is a natural human impulse to think of evolution as a long chain of improvements, of a never-ending advance toward largeness and complexity—in a word, toward 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 eye, and even they contain species that are microscopic. Indeed, according to Woese, if you totaled up all the biomass of the planet—every living thing, plants included—microbes would account for at least 80 percent of all there is, perhaps more. The world belongs to the very small—and it has for a very long time.
人们自然会不由自主地想到，进化是个不断完善的漫长过程，一个朝着更大、更复杂的方向——一句话，朝着形成我们的方向——永远前进的过程。我们是自己奉承自己。在进化过程中，实际差异在大多数情况下向来是很小的。出现我们这样的大家伙完全是一种侥幸——是一种有意思的次要部分。在23种主要生命形式中，只有3种——植物、动物和真菌——大到人的肉眼能看得见的程度。即使在它们中间，有的种类也是极小的。据沃斯说，即使你把植物的全部生物量加起来——包括植物在内的每一生物，微生物至少要占总数的80%，也许还多。世界属于很小的生物——很长时间以来一直如此。

So why, you are bound to ask at some point in your life, do microbes so often want to hurt us? What possible satisfaction could there be to a microbe in having us grow feverish or chilled, or disfigured with sores, or above all expire? A dead host, after all, is hardly going to provide long-term hospitality.
因此，到了生命的某个时刻，你势必会问，微生物为什么那样经常地想要伤害我们？把我们弄得发烧，或发冷，或满身长疮，或最后死掉，对微生物来说到底会有什么好处？毕竟，一个死去的寄主不大能提供长期而适宜的环境。
To begin with, it is worth remembering that most microorganisms are neutral or even beneficial to human well-being.
首先，我们应当记住，大部分微生物对人体健康是无害的，甚至是有益的。