A new view for studying and understanding biological evolution emerges when the concepts of phylogenetic systematics and exaptation are combined. A new definition of macroevolution is created. Preadaptation is shown to be a null concept and its comparison with exaptation is shown to be inappropriate. This book criticizes the prevailing view, the adaptationist, microevolutionary outlook, which considers adaptation as being the exclusive or main evolutionary process responsible for vertebrates having occupied the terrestrial environment. The authors argue that the macroevolutionary processes are significantly more important to explain an improbable evolutionary event. Their research shows that macroevolutionary processes are the dominant factors involved in the origin of terrestriality.