But we will concede that every creature bore a charmed life, that it might not perish by famine or violence till it had propagated its kind. We should then expect to observe that species had distributed themselves over the globe in lines either tortuous or direct, single or branching, broad or narrow, but all diverging from a common centre. Yet nothing of the kind is found. On the contrary, the species of the new world differ from those of the old, the species of one continent from those of another[18]. The marsupials of Australia and Polynesia are generically distinct from all other animals on the globe except the opossum. The elephant of Africa is not the same species as the elephant of India: so with the lion, so with the rhinoceros. The apes and baboons of the old world are nowhere to be found in America, nor the American monkeys anywhere in the old world. In Madagascar, separated from Africa by less than the breadth of England, all the species except one, and nearly all the genera, are peculiar[19]. Everywhere species are found limited in their range by natural barriers, such as climate, rivers, mountains, oceans. Are we to suppose that the prisoners could scramble into their prisons, and then suddenly became incapable of scrambling out again? Everywhere, as a rule, this range is consistent with the hypothesis of an origin central to the range, inconsistent with that of an origin distant from it. Where, as on mountain ranges, we find, contrary to the general rule, the same species in different localities, the migration from the door of the ark loses all semblance of probability, unless we are pleased to imagine that creatures, now without the instinct of migration, for a long time possessed it, and roamed about the world through many a sultry plain to pick out a hill-side here and there with a temperature suited to their constitutions. But the exceptional phenomenon, otherwise so hard to account for, Darwin has admirably explained, by pointing out that species adapted to a low temperature would naturally have occupied lowlands in the Glacial Period, from which, as the cold gradually grew less and less intense, they would as naturally have retired, some of them northwards, others to the cool heights of various mountains. That there was a Glacial Period, when great icebergs travelled over England, a period geologically as but of yesterday, though enormously more remote than any historical dates, is now beyond all question. Equally beyond question is it that countless ages and generations of living beings on the earth preceded that Glacial Period. And, added to this, we find that there are forms of life just where they would have been left by the effect of that period, had there been an unbroken succession from that time to this, and just where it is most unlikely they should be found, had they been forced to travel to those habitations from the door of the ark within the practically insignificant period of 4300 years.