A possible connection has been suggested by Sergi between the Mas-d'Azil signs and the markings that have been discovered on the megalithic monuments of North Africa, Brittany, and the British Isles. These are all so rudimentary that resemblances are inevitable, and of themselves afford little ground for necessary connections. Primitive man is but a child, and all children bawl and scrawl much in the same way. Nevertheless C. Letourneau[121] has taken the trouble to compare five such scrawls from "Libyan inscriptions" now in the Bardo Museum, Tunis, with similar or identical signs on Brittany and Irish dolmens. There is the familiar circle plain and dotted [Symbol] [Symbol], the cross in its simplest form [Symbol], the pothook and segmented square [Symbol], all of which recur in the Phoenician, Keltiberian, Etruscan, Libyan or Tuareg systems. Letourneau, however, who does not call them letters but only "signes alphabetiformes," merely suggests that, if not phonetic marks when first carved on the neolithic monuments, they may have become so in later times. Against this it need only be urged that in later times all these peoples were supplied with complete alphabetic systems from the East as soon as they required them. By that time all the peoples of the culture-zone were well-advanced into the historic period, and had long forgotten the rude carvings of their neolithic forefathers. Armed with a nearly perfect writing system, and the correlated cultural appliances, the higher races soon took a foremost place in the general progress of mankind, and gradually acquired a marked ascendancy, not only over the less cultured populations of the globe, but in large measure over the forces of nature herself. With the development of navigation and improved methods of locomotion, inland seas, barren wastes, and mountain ranges ceased to be insurmountable obstacles to their movements, which within certain limits have never been arrested throughout all recorded time. Thus, during the long ages following the first peopling of the earth by pleistocene man, fresh settlements and readjustments have been continually in progress, although wholesale displacements must be regarded as rare events. With few exceptions, the later migrations, whether hostile or peaceful, were, for reasons already stated[122], generally of a partial character, while certain insular regions, such as America and Australia, remained little affected by such movements till quite recent times. But for the inhabitants of the eastern hemisphere the results were none the less far-reaching. Continuous infiltrations could not fail ultimately to bring about great modifications of early types, while the ever-active principle of convergence tended to produce a general uniformity amongst the new amalgams. Thus the great varietal divisions, though undergoing slow changes from age to age, continued, like all other zoological groups, to maintain a distinct regional character.