The Origin of Species Chapter 12 Part 2 - Geological Distribution

In which the means by which plants and animals have been dispersed over vast and diverse regions are carefully examined, with a special emphasis on the effects of past glacial periods that once altered climates and shaped the distribution of species on distant mountains and continents. It is proposed that alternating glacial conditions in opposite hemispheres influenced migration patterns and the mingling of flora and fauna, leaving enduring traces upon the inhabitants of distant and isolated lands.