Chapter 11: Geographical Distribution Summary and Analysis

It is obvious that differences in climate and terrain are not sufficient to account for the differences in organisms from one region to the next. This is a conclusion admitted by almost all naturalists who have studied the subject. This point can be illustrated by considering North America and Europe. Very few climates on either continent do not have a counterpart in the other. Nonetheless, the variety of plants and animals in each is completely different. The same is the case with South America, Africa, and Australia.

The existence of barriers within regions is also correlated with a difference in the creatures that inhabit that region. Thus, for example, the kinds of land animals that are found to exist on one side of a mountain often differ greatly from those that live on the other side. The...