In the earliest stages of man’s development he had no more need of money than animals have. He was content with very simple forms of shelter from natural materials around him. he made his own rough tools and weapons. As he became more civilized, however, he began to want better shelter, more efficient tools and weapons, and more comfortable clothing than could be provided by the work of his own unskilled hands. For these things he had to turn to the skilled people such as smiths and carpenters who were springing up everywhere. It was then that the question of payment arose At first he got what he wanted by a simple process of exchange. The smith who had not the time to look after land or cattle was glad to take meat or grain from the farmer in exchange for an axe or a plough. But as more and more goods which had no fixed exchange value came on the market, exchange became too complicated to be satisfactory. Another problem arose when those who made things wanted to get stocks of wood leather, or iron, but had nothing to offer in exchange until their finished goods were ready. Thus the difficulties of exchange led by degrees to the invention of money. In some countries, easily handled things like seeds or shells were given a certain value and the farmer, instead of paying the smith for a new axe by giving him some meat or grain, gave him so many shells. If the smith had any shells left when he had bought his food, he could get stocks of the raw materials of his trade. In some countries quite large things such as cows or camels or even big flat stones were used for trade. Later, pieces of metal, bearing values according to the rarity of the metal and the size of the pieces, or coins were used. Money as we know it had arrived. 3. Exchange of goods became difficult because ________.