ANTA01H3 Lecture Notes - Lecture 2: Irreversible Process, Adaptive Radiation
Document Summary
Many times during the long history of life, advanced organism have returned to ancestral habits and modes of life. Study of such cases suggests that due to commonalty of environment and resultant functional adaptation, always a gross similarity between ancestral and descendent structures is achieved without any genuine reversal at all. Thus many reptiles and mammals have reverted to an aquatic mode of life. They have assumed a generally streamlined, fishlike form, and the limbs have become shortened, webbed and finlike. Yet the skeleton of such flippers is always distinctly that of the class to which animal belongs rather than that of a fish fin. The evidence indicates that major evolutionary steps once taken, are never reversed. This is known as dollo"s rule after louise dollo(1895) to whom the principal is ascribed. It might even expected a priori, major evolutionary steps are compound of many smaller steps, each preserved by natural selection.
