=Nature’s Contributions to Production.=—Nature contributes to the production of economic goods such things as land, timber, waterways for transportation, minerals, coal and oil, the motive power of steam,—in a word nature provides all the materials and the environment of production. Hence it is fundamentally the most important of all the factors. If one studies the history of those nations which have become great in various periods in history, it will be found that the basis of their material greatness was in practically every case the bounty of nature. Civilization made its first advance in the fertile valleys of the Euphrates and the Nile. Its progress since the dawn of history has been conditioned by man’s success in discovering and using natural resources. Among the contributions of nature to production some, such as land, can be brought under private ownership. So long as land was plentiful and population scanty there was no occasion for private property in land. When Caesar first came into contact with the Teutonic tribes he found that land was not held in private ownership. Everyone took what he wanted; when the land seemed to be growing exhausted the whole tribe moved on to some other region. But as these tribes grew in number and unoccupied land became less plentiful, common ownership gave way to private ownership. The Anglo-Saxons had reached this stage before they migrated to England. [Sidenote: Rent.] Land held in private ownership can be bought, sold, and leased. When it is leased, the owner receives for its use a payment known as rent. Rent may be defined as the return which is obtained by the owner of any form of natural resource. This includes not only land but mines, water-powers, trout-streams, and so forth. The return which is received for the use of unimproved land is usually called _ground rent_, while the return which results from improvements such as buildings upon the land, fences, and drains is called _improvement rent_. Strictly speaking, this is not rent, but a return upon invested capital. The amount of ground rent paid for any piece of land depends upon its relative fertility, if it is to be used for agriculture, and its location. Location alone determines the ground rent of land in towns and cities. [Sidenote: What is labor?] =Labor as a Factor in Production.=—What is labor? Is all muscular and mental exertion entitled to be called labor? Mountain climbing involves the most severe sort of bodily effort. Tourists do it for pleasure and guides do it for pay. Is it labor in one case and not in the other? Some men play chess for recreation; others make a living out of it; in either case there is strenuous mental exertion involved. So where does labor begin and end?