It is worthy of notice that, when Pithecanthropus was alive, "Java was a part of the Asiatic continent; and similar herds of great mammals roamed freely over the plains from the foot-hills of the Himalaya Mountains to the borders of the ancient Trinil River, while similar apes inhabited the forests. At the same time the Orang may have entered the forests of Borneo, which are at present its home."[13] Where man's distant cousins, the anthropoid apes, and his still nearer relation, Pithecanthropus, were all living and some, at least, apparently progressing, could hardly have been far from his original home. But the climatic conditions of that time lead us to seek his original cradle somewhat farther northward than India, or even Beluchistan, and nearer to, if not in, the great steppe zone of central Asia. We lose sight of our ape-man as he is advancing toward the threshold of manhood, not far away. Whether we think that Pithecanthropus was approaching or had already passed it depends much upon where we draw the line between ape and man, a line largely artificial and as difficult to fix as the day and hour when the youth becomes of age, and what human characteristics we select to mark it. In his erect posture and some other physical traits he seems already to have attained manhood; mentally he was probably far inferior to even the lowest savage races of to-day. We are not sure whether he was our ancestor or merely a cousin of our ancestor, once or twice removed; we still lack foundations for any hypotheses as to exactly when, where, or how the erect ancestral ape-man emerged into real manhood. Millennia passed between the days of Pithecanthropus and the first human migrations, and we may imagine primitive man as having become fairly well accustomed to life on the ground, and as having mastered his first lessons in meeting its dangers and difficulties. He had probably taken possession of a much wider area than the home of the ape-man, perhaps of the whole of the parkland zone curving around the western buttresses of the plateau of Thibet. From this region routes of migration radiated in all directions, all the more open because of the elevation of land which lasted through Upper Pliocene and early Pleistocene times.[14] Sumatra and Java then formed an extension of the Malay Peninsula, reaching more than 1,000 miles into the Indian Ocean; while the Orang seems to have been able to reach Borneo somewhat earlier. The way was equally clear westward into Europe, the Dardanelles being then replaced by a land bridge, while a second bridge spanned the Mediterranean over Sicily into Italy, and a third existed at Gibraltar.[15] These routes were evidently followed by herds of great herbivora, and probably by the earliest human emigrants into Europe. Following Keane,[16] we shall divide mankind into four great groups or races, and then glance at their radiation from southwestern Asia toward all parts of the globe. These great primitive divisions are: