Taking Evolutionary Transitions Seriously

The distinction between reversible and irreversible phenomena in biological information systems provides a basis for distinguishing microevolution from macroevolution. Biological transitions encompass the entire class of irreversible changes in biological systems, including physiological and developmental phenomena. Evolutionary transitions are the subset of biological transitions that have an impact on the quality and quantity of biological information transmitted to future generations. Evolutionary transitions are manifested empirically as macroevolutionary changes, i.e. evolutionary changes that can be detected only through phylogenetic analysis among groups of species sharing a unique common ancestry. 1 TWO RECENT PERSPECTIVES The past 20 years have witnessed significant conceptual breakthroughs in understanding the fundamental nature of biological systems, and their evolutionary fate over space and through time (see, e.g., references in Brooks, 2000, 2001 and in this contribution). I believe that such conceptual advances (the ‘text’ of biological theory) must become embedded in ongoing empirical biological research (the ‘context’ of biological theory) if they are to have lasting impact. In this contribution, I will first discuss two complementary conceptual views of biological evolution, that of Brooks and Wiley (1988) and of Maynard Smith and Szathmary (1995). I will then propose a simplified taxonomy of biological and evolutionary transitions stemming from those views, within which the ‘major transitions’ of Maynard Smith and Szathmary (1995) nest. Finally, I will briefly discuss