Physical relationship between islands and peninsulas--Character of insular flora and fauna--Paradoxical influences of island habitat on man--Conservative and radical tendencies born of isolation and accessibility--Islands as nurseries and disseminators of distinctive civilizations--Limitation of small area in insular history--Sources of ethnic stock of islands on nearest mainland. Ethnic divergence with increased isolation--Differentiation of peoples and civilizations in islands--Differentiation of language--Unification of race in islands--Remoter sources of island populations--Double sources--Mixed population of small thalassic isles--Significant location of island way stations--Thalassic islands as goals of maritime expansion--Political detachability of islands--Insular weakness based upon small area--Island fragments of broken empires--Area and location as factors in political autonomy of islands--Historical effects of island isolation in primitive retardation--Later stimulation of development--Excessive isolation--Protection of an island environment--Islands as places of refuge--Islands as places of survival--Effects of small area in islands--Economic limitations of their small area--Dense population of islands--Geographic causes of this density--Oceanic climate as factor--Relation of density to size--Density affected by a focal location for trade--Overflow of island population and colonies to the mainland--Precocious development of island agriculture--Intensive tillage--Emigration and colonization from islands--Recent emigration from islands--Maritime enterprise as outlet--Artificial checks to population--Polyandry--Infanticide--Low valuation of human life. CHAPTER XIV. PLAINS, STEPPES AND DESERTS Relief of the sea floor--Mean elevations of the continents--Distribution of relief--Homologous reliefs and homologous histories--Anthropo-geography of lowlands--Extensive plains unfavorable to early development--Conditions for fusion in plains--Retardation due to monotonous environment--Influence of slight geographic features in plains--Plains and political expansion--Arid plains--Nomadism--Pastoral life--Pastoral nomads of Arctic plains--Historical importance of steppe nomads--Mobility of pastoral nomads--Seasonal migrations--Marauding expeditions--Forms of defense against nomad depredations--Pastoral life as a training for soldiers--Capacity for political organization and consolidation--Centralization versus decentralization in nomadism--Spirit of independence among nomads--Resistance to conquest--Curtailment of nomadism--Supplementary agriculture of pastoral nomadism--Irrigation and horticulture--Scant diet of nomads--Effects of a diminishing water supply--Checks to population--Trade of nomads--Pastoral nomads as middlemen--Desert markets--Nomad industries--Arid lands as areas of arrested development--Mental and moral qualities of nomads--Religion of pastoral nomads. CHAPTER XV. MOUNTAIN BARRIERS AND THEIR PASSES