One thing we seem to be able to see, in the food-collecting era in general, is a tendency for people to begin to settle down. This settling down seemed to become further intensified in the terminal era. How this is connected with Professor Mathiassen’s “receptiveness” and the tendency to be experimental, we do not exactly know. The evidence from the New World comes into play here as well as that from the Old World. With this settling down in one place, the people of the terminal era--especially the “Forest folk” whom we know best--began making a great variety of new things. I remarked about this earlier in the chapter. Dr. Robert M. Adams is of the opinion that this atmosphere of experimentation with new tools--with new ways of collecting food--is the kind of atmosphere in which one might expect trials at planting and at animal domestication to have been made. We first begin to find traces of more permanent life in outdoor camp sites, although caves were still inhabited at the beginning of the terminal era. It is not surprising at all that the “Forest folk” had already domesticated the dog. In this sense, the whole era of food-collecting was becoming ready and almost “incipient” for cultivation and animal domestication. Northwestern Europe was not the place for really effective beginnings in agriculture and animal domestication. These would have had to take place in one of those natural environments of promise, where a variety of plants and animals, each possible of domestication, was available in the wild state. Let me spell this out. Really effective food-production must include a variety of items to make up a reasonably well-rounded diet. The food-supply so produced must be trustworthy, even though the food-producing peoples themselves might be happy to supplement it with fish and wild strawberries, just as we do when such things are available. So, as we said earlier, part of our problem is that of finding a region with a natural environment which includes--and did include, some ten thousand years ago--a variety of possibly domesticable wild plants and animals. NUCLEAR AREAS Now comes the last of my definitions. A region with a natural environment which included a variety of wild plants and animals, both possible and ready for domestication, would be a central or core or _nuclear area_, that is, it would be when and _if_ food-production took place within it. It is pretty hard for me to imagine food-production having ever made an independent start outside such a nuclear area, although there may be some possible nuclear areas in which food-production never took place (possibly in parts of Africa, for example).