Peculiarly enough, it was a matter of topography. The plateau which reached above the clouds rose with a steep slope from the valley in which Burl and the others had lived. To westward, however, the highland was subject to an indentation which almost severed it. No more than twenty miles from where Burl's group had climbed to sunshine, there was a much more gradual slope downward. There, mushroom-forests grew almost to the cloud-layer. From there, giant insects strayed up and onto the plateau itself. They could not live on the plateau, of course. There was no food for their insatiable hunger. Especially at night, there was no warmth to keep them active. But they did stray from their normal environment, and some of them reached the sunshine, and perhaps some of them blundered back down to their mushroom-forests again. But those that did not find their way back were chilled to torpor during their first night on the highland. They were only partly active on the second day if, indeed, they were active at all. And few or none recovered from the second night of cold. Certainly none kept their full ferocity and deadliness. And this was how the dogs survived. Unquestionably the dogs were descended from dogs on the wrecked ship--name now unknown--which had landed on this planet some forty-odd human generations since. The humans had no memories of that ship, and the dogs had surely no traditions. But perhaps because those early dogs had less of intellect, they had possessed more useful instincts. Perhaps dogs were bred by the first desperate generations of humans, to warn them against dangers. But no human civilization could survive the environment of the lowlands. The humans inevitably reverted to the primitive. The environment was not one in which dogs could survive, so somehow they took to the heights. Perhaps dogs survived their masters. Perhaps some were abandoned or driven away. But dogs had reached the heights. And they did survive because of the simple fact that giant insects blundered up after them--and could not survive the proper environment for dogs and men. There was even a reason why they had not multiplied excessively. The food-supply was limited. When there were too many dogs, their attacks on stumbling insects were more desperate, and made earlier before ferocity of the insects was lessened. And more dogs died. So there was a specific adjustment of the dog population to the food-supply. There was also a selection of those intelligent enough not to attack foolishly, but not of those whose cowardice left them out of conflict altogether.