The reason I tell you about the glaciers is simply to remind you of the changing world in which prehistoric men lived. Their surroundings--the animals and plants they used for food, and the weather they had to protect themselves from--were always changing. On the other hand, this change happened over so long a period of time and was so slow that individual people could not have noticed it. Glaciers, about which they probably knew nothing, moved in hundreds of miles to the north of them. The people must simply have wandered ever more southward in search of the plants and animals on which they lived. Or some men may have stayed where they were and learned to hunt different animals and eat different foods. Prehistoric men had to keep adapting themselves to new environments and those who were most adaptive were most successful. OTHER CHANGES Changes took place in the men themselves as well as in the ways they lived. As time went on, they made better tools and weapons. Then, too, we begin to find signs of how they started thinking of other things than food and the tools to get it with. We find that they painted on the walls of caves, and decorated their tools; we find that they buried their dead. At about the time when the last great glacier was finally melting away, men in the Near East made the first basic change in human economy. They began to plant grain, and they learned to raise and herd certain animals. This meant that they could store food in granaries and “on the hoof” against the bad times of the year. This first really basic change in man’s way of living has been called the “food-producing revolution.” By the time it happened, a modern kind of climate was beginning. Men had already grown to look as they do now. Know-how in ways of living had developed and progressed, slowly but surely, up to a point. It was impossible for men to go beyond that point if they only hunted and fished and gathered wild foods. Once the basic change was made--once the food-producing revolution became effective--technology leaped ahead and civilization and written history soon began. Prehistoric Men THEMSELVES [Illustration] DO WE KNOW WHERE MAN ORIGINATED? For a long time some scientists thought the “cradle of mankind” was in central Asia. Other scientists insisted it was in Africa, and still others said it might have been in Europe. Actually, we don’t know where it was. We don’t even know that there was only _one_ “cradle.” If we had to choose a “cradle” at this moment, we would probably say Africa. But the southern portions of Asia and Europe may also have been included in the general area. The scene of the early development of mankind was certainly the Old World. It is pretty certain men didn’t reach North or South America until almost the end of the Ice Age--had they done so earlier we would certainly have found some trace of them by now.