BIOGEOGRAPHY
Alfred Russell Wallace, the co-author of the theory of evolution by natural selection, was also known as the "father of biogeography." Wallace established biogeography (the study of the past and present geographical distribution of organisms) by studying the distribution of animal species around the world. Some animals are found in one region and not in others. There are patterns in how species occur geographically, based on such factors as where they evolved, how far they dispersed, and how changes in the Earth affected their distribution. The discovery of Mesosaurus fossils in South America and Africa, for example, can be explained by the fact that the continents once formed a single land mass. Mesosaurus, an aquatic reptile adapted to fresh water, lived in the Permian period, more that 250 mya. South America, Africa, and the other continents were still joined at that time.

Biogeographic distributions demonstrate the fact that species have evolved under differing conditions in different parts of the world. Isolation of related forms over time in different environmental conditions results in the development of new specializations.