Origin of Species Variorum

humidity, &c.; and various animals and plants will have migrated in different proportions and at different rates. So that altogether during the Glacial period the inhabitants of the tropics must have been greatly disturbed in all their relations of life. ↑ Hence they will have suffered much extinction; how much no one can say; perhaps formerly the tropics supported as many species as we now see crowded together at the ... Cape of Good Hope, and in parts of temperate Australia. As we know that many tropical plants and animals can withstand a considerable amount of cold, many might have escaped extermination during a moderate fall of temperature, more especially by escaping into the lowest, most protected, and warmest districts. Nor must it be overlooked that, as the cold will have come on very slowly, it is almost certain that many of the inhabitants of the tropics will have become in some degree acclimatised; in the same manner as the same species of plant when living on lowlands and highlands certainly transmit to their seedlings different constitutional powers of resisting cold. Nevertheless, it cannot be denied that all tropical productions will have greatly suffered, and the chief difficulty is to understand how they can have escaped entire annihilation. ↑ On the other hand, the temperate productions, after migrating nearer to the equator, though they will have been placed under somewhat new conditions, will have suffered less. And it is certain that many temperate plants, if protected from the inroads of competitors, can withstand a much warmer climate than that proper to them. Hence, it seems to me possible, bearing in mind that the tropical productions were in a suffering state, and could not have presented a firm front against intruders, that a certain number of the more vigorous and dominant temperate forms might have penetrated the