When some prehistoric man, wounded and hungry (as he always was), stepped out onto the plain, he could find around him what he needed to survive. He could find plants and animals to eat, and those plants and animals would provide him with just enough energy to find more plants and animals, and when a little energy was left over, he could find some material to shelter him from the elements.

But of course, the animals didn’t lay down and offer themselves to him. The rocks cleaved to the earth; the plants tried to hold fast in the ground. The sad fact is that work was required. Work, stone-cold work, made the difference between life and death. But at least he could do it. And with each hard meal, and with each driving rain or bitter cold snap that he passed warm and dry, prehistoric man gained another day. But only having another day was not enough to satisfy him, not enough to convince him to rest.