Page:Popular Science Monthly Volume 60.djvu/382

374 the Himalayan line. In these early days, moreover, the penisulapeninsula [sic] portion of the Old World constituted a practically continuous land-mass. Toward the west India was connected with Africa, and Africa was joined to Europe by two or more isthmuses. In the opposite direction, the Malaysian peninsula was extended toward Australia through what are now the separate islands of Sumatra, Borneo and Java; Australia was likewise connected with New Guinea, and the immense island continent thus constituted was to all intents and purposes coterminous with the southeasterly extensions of Malaysia. It must have been possible, therefore, at this time for primeval man to proceed from the Indo-Malaysian abode along the central latitudes, to the Atlantic on the west, and far out across the Pacific on the east, without having to cross the open seas.

During the course of the pleistocene period the ice disappeared from the north and glaciation set in from the south, the glaciers in this instance proceeding from the antarctic regions and from the highlands of the southern peninsulas. The thermal equator also moved north of the geographical equator at this time, and during the long interglacial epoch that followed, lasting at least ten thousand years, the whole Northern Hemisphere enjoyed an equable climate, ranging from tropical to temperate conditions and devoid of great seasonal variations. The effect of this change must have been to limit the lines of migration toward the far south, and greatly to extend the course of dispersion towards the northeast and northwest. Or to put it more exactly: entry into South Africa was probably barred by the increasing cold, but as the influence of the southern glaciers did not extend as far north as the Indo-Mediterranean-Malaysian belt, the inhabitants of this region were doubtless free to wander east and west as before along the central latitudes. Nor did climatic conditions any longer prevent men from penetrating into the continental area beyond. Mountain masses still barred the way in the center, to be sure; but passages were open on either side; from the Mediterranean region into Europe, and from the Malaysian region into Asia. Above the Himalayan line the Tibetan plateau interposed itself between these Mediterranean and Malaysian emigrants and probably kept them for long ages apart. For this reason, and doubtless also because the maritime regions offered greater attractions to primeval man than the inland areas, the earliest lines of migration appear to have followed the Atlantic and Pacific coasts of the Eastern Hemisphere into the northern latitudes, where the shore lines of the Eurasian continent stretch out toward America. During the first and second interglacial epochs the two hemispheres were, indeed, practically coterminous in these parts. This was due to the fact that the level of the northern oceans was lowered at these times, leaving land-bridges exposed to view which have since become covered by the sea. As a result, the