from pasturage to agriculture in seventh-century Ireland, says: "Because of the abundance of the households, in their period, therefore it is that they [the sons of Ed Slane] introduced boundaries in Ireland." Jenks tells us that the earliest cultivators of the soil were "strangers attached to the tribe upon whom the rough work of the community fell, and who would be the first to suffer from scarcity of food." Elsewhere we are told: "When hemmed in by impassable barriers or invincible enemies, pastoral tribes under the pressure of increasing population slowly become agricultural." To the same force is due the change from extensive and shifting cultivation, where after a crop or two the cultivator makes a fresh clearing, to intensive agriculture, where by an alternation of crops and fallow the same land is used in perpetuity.

Now, through these economic changes the movement of population becomes a primary cause of the changes in social organization to which they give rise. The adoption of pastoral pursuits converts the savage pack into the tribe, institutes property, establishes male kinship, develops patriarchal authority, favors polygyny and wife-purchase, makes woman a chattel, causes captives to be enslaved instead of eaten, and substitutes the wergeld for the blood-feud. The adoption of agriculture changes the nature of the social bond. Says Maine: "From the moment a tribal community settles down finally upon a definite space of land, the land begins to be the basis of society in place of kinship." It breaks up the tribe into clans which become village communities. The back-breaking toil induces a resort to systematic slavery and the slave trade. Where settlement has already occurred, the passage from simple collection to tillage causes a passage from the large patriarchal household to the simple family, and from family property in land to individual property with the right of bequest.

After agriculture is adopted, the increase of population does not cease to be a dynamic factor. The land is progressively occupied, until at last the laborer has no longer a direct access to natural resources, but must offer his services for wages. When this point is reached, slavery and serfdom begin to disappear, for coercion is no longer necessary to secure a supply of laborers.

The expansion of population compels a resort to inferior soils, which, by enhancing the value of good land and increasing the landowner's share of the produce, engenders an agricultural aristocracy, which, as it withdraws itself entirely from labor and concentrates its attention on war and politics, becomes master of the community.

Again, the enlargement of demand in consequence of the increase of numbers enables an exchange economy to take the place of domestic husbandry, perhaps causes a foreign trade to spring up. The growth of potential exchange, in consequence of the greater local surpluses to be disposed of and the greater local deficits to be supplied from outside sources, makes it worth while to create avenues of communication, and these, in turn, promote the territorial division of labor. The growth of numbers in a region cannot but strain its natural resources in certain respects and compel the local population to supply their lack of certain commodities from the larger resources of some other locality, sending out in return those products of their own region which are to be had in the greatest abundance. Besides calling into being merchants, markets, and movements of goods, the expansion of population causes local groups of craftsmen to spring up for the supplying of articles formerly demanded in quantities too small to set up currents of trade. In place of the transitory assemblages at fairs, there now appear town populations regularly exchanging their wares with the country.

The growing prominence of exchange brings men into unwonted relations, which presently call forth an expansion of law on the commercial side. The appearance of routes traversing many jurisdictions, and the need of a more perfect security to goods en route or in a market, create a demand for royal protection and cement that alliance of the nascent merchantartisan groups with the king which is so potent in humbling the feudal lords. The monarch, finding his surest support in his struggle with the barons in the burgher population, picks from them his agents and servants, and the choicest of these, ennobled by royal patent, take their places alongside the old territorial aristocracy.

The towns which arose in the Middle Ages to meet the needs of an expanding population became the starting-point of social and political developments quite tangential to the institutions of the time. The manor was a type of constrained association; the town, of free association. "City air makes free." Outside the town the industrial classes were servile, and a stigma attached to labor; inside, labor was honored, and the workman felt joy and pride in his work. Outside, fighting and working were distinct professions; inside, the burgher labored or fought as occasion required. Outside was rigid hereditary caste; inside, men stood in multiple and fluid relationships. The town, in fact, contained the germ of a distinct social growth. How pregnant is the overflow of population into towns appears from the fact that town life develops a mentality of its own, more impressionable and plastic than that of the country. Here outworn traditions and narrow sentiments and obstinate prejudices cancel one another. Races fuse and intermarry. There appear new combinations of hereditary factors. Variation is more common. The shutters of the intellect are taken down. The mind becomes alert and supple. Freed from the hampering net of kin and class ties, the individual appears. The town is, therefore, a hotbed, where seed-ideas quickly germinate. Its progressive population soon places itself at the head of the social procession, and sets the pace for the conservative country.

The city, less traditional than the country, values men according to some present fact their efficiency or their wealth, rather than their family. It is democratic or plutocratic in temper, while the country is the natural support of aristocracy. In the city people consume, as it were, in one another's presence, and hence their expenditure conforms more to the canon of Conspicuous Waste than does that of countrymen. The multiplication of merely conventional wants arouses energy, intensifies competition, whets egoism, and restricts the size of the family.

The increase of social mass has various effects upon regulative institutions. A lateral extension of society, by causing distinctions to arise between local chiefs and the head chief, between local priests and the high priest, favors the formation of hier

archies. The growth of the aggregate causes a differentiation between sacred and secular functionaries, between military and civil heads, and between judicial, legislative, and executive offices. The heavier burden of business compels the ruler to surround himself with helpers, who in turn require other helpers, until government structure becomes complex. Power is deputed and re-deputed. Control comes into the hands of the leisured or the trained. The exclusion of the poorer classes from the government of the Roman republic in its later period was due to its expansion. "Now that Rome had ceased to be a purely Italian state, and had adopted Hellenic culture, it was no longer possible to take a small farmer from the plow and set him at the head of the community." Eventually, owing to the overflow of population into the great burgess-colonies, and the diffusion of the Romans throughout the peninsula, the absolute centralization in the one focus of Rome was given up, and a municipal system was instituted for Italy which permitted the formation of smaller civic communities within the Roman community. "Under Chlodovech and his immediate successors," we read, "the People, asembled in arms, had a real participation in the resolutions of the king. But with the increasing size of the kingdom, the meeting of the entire people became impossible." In New England, after the local community reaches a certain size, the annual townmeeting is replaced by the government by mayor and council.

There is, furthermore, reason to believe that the formation of large, dense, complex bodies of population is favorable to the growth of a belief in the rights of man as man and to the spread of ideas of human equality, i. e., of the habits of thought that underlie individualism and democracy.

So far, the growth of population has been assumed to proceed at an equal rate throughout society. If, now, it be assumed that the rate of increase is sensibly unequal, a new set of consequences appears. The resulting inequality of pressure-providing the distribution of life-opportunities remains the same—will cause people to pass from class to class and from place to place. City dwellers never keep abreast of country dwellers in reproduction, and hence the city has constantly to be fed with the overflow from

the farms. One consequence is that the city never becomes traditional and static, as it might well do if it grew from its own loins. Another result is the gradual depletion of the eugenic capital of the rural population-e. g., the increasing brachycephaly of France within historic times-owing to the continual drain of its best elements to the cities. As the towns draw from the fields, so the fertile valleys, sterilized by their very prosperity, draw from the barren uplands streams of migrants representing the peoples beaten in ancient conquests.

It may happen that the distinct types in the population - the martial and the industrial, the imaginative and the calculating, the "ideo-motor" and the "critical-intellectual "- come under diverse influences which make their rates of reproduction unequal, and so change their numerical proportions. Every such shifting of the predominant type is marked by important vicissitudes in society.

The unequal increase of population on the opposite sides of a frontier finally sets up a current of migration which replaces one race, language, or civilization by another, thereby entailing changes in society. If the frontier is a political one, the movement is likely to take the form of an armed invasion, and the society must sustain the shock of war. It is now understood that the assaults of the Germans upon the Roman empire were prompted by overpopulation, and the eventual failure to withstand them was due to the fact that infecundity had reduced the empire to a hollow shell.

II. The accumulation of wealth.-The progress of wealth, and the expansion of income which attends the control of a growing mass of capital, have a transforming effect on society. Even a general movement of prosperity shared in by all is a dynamic factor. The enlarged production shows itself, not along the entire line of commodities, but chiefly in the higher grades of goods, and in comforts and luxuries. These qualitative changes in production cannot but result in the transfer of labor and capital from certain occupations to others, from extractive to elaborative industries, from the production of goods to the supplying of services, from certain centers and regions to other