背景：网上找了很久没找到原文。下面是比较接近的内容，大概说了一下两种理论。
Those highly specialized animals iliving entirely in the groundwater environment, and absent in surface waters, are called stygobites. 接下来说stygobites都有什么习性，包括哪些动物（记得有说蛇）。There are two main theories of cave colonization and troglobite evolution: 1. the pleistocene effect theory (Barr and Holsinger), 2. the adaptive shift theory (Howarth). The Pleistocene effect has been the most widely accepted model for the evolution of terrestrial troglobites until quite recently, During cold glacial climates, the cooler, wetter conditions south of the continental ice masses of Europe, Asia and America favoured the spread of invertebrates inhabiting both temperate forest ecosystems and caves. With the ameliorations of climate, those taxa that survived were those living in caves as the forest ecosystmes changed radically. Ultimately geographic and genetic isolation in these cave rerugia produced adaptive radiation and the evolution of distinct troglobites. In favor of this theory are the close affinities between closed forest and cave taxa, the present distributions of taxa in mountain areas separated by deep valleys, and former wider distributions evidenced from the fossil record.
The second theory, that of adaptive shift, was advanced by Howarth to explain the origin of troglobites in the Hawaiian lava tubes, but many have much wider applicability. This theory does not rely on climate change; rather it proposes that partially adapted ancestral species moved into cave niches almost continuously. These may have been species out-competed in surface environments. Thus the availability of food is the keystone of this theory, and troglobite evolution has been continual rather than episodic.这是关于第一种P理论的补充知识（没有在考试文章出现，不过对理解有帮助）The pioneering studies of cave life were predominantly carried out in the karst areas of Europe and North America, areas directly or closely associated with regions repeatedly covered by ice during the Pleistocene. Hence, the effects of glaciation came to dominate the debate about both the distribution and the origin of troglobitic animals. The classic view of the evolution of terrestrial troglobite is, in essence, that climatic instability in the surface environment - especially changes to cold and arid conditions associated with the onset and retreat of Pleistocene glaciations - led to the extinction of surface populations of species that mostly lived in forest soil and litter. This process disrupted interbreeding between the various troglophilic populations and permitted adaptation to the cave conditions in the now-isolated cave populations.
