Agosta, Salvatore J., and Daniel R. Brooks. “Evolutionary Transitions.” In The Major Metaphors of Evolution , pp. 193-218. Springer, Cham, 2020.
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Evolutionary transitions are episodes of conflict resolution resulting in irreversible changes in inheritance systems. The Tree of Life is a record of these transitions, a story of the ongoing saga of evolvable life on this planet since its inception some 3.5 billion years ago. Each episode in the saga highlights the open-endedness of evolution and the indefinite capacity of evolvable life to cope with changes in the conditions by using inherited information to buy time for continued survival. It is during these periods that evolutionary innovations emerge from the indefinite variation that is a property of inheritance systems, resolving conflicts and resulting in selective diversification. The highly conservative nature of the inheritance systems allows us to retrace this history using phylogenetic analysis. Phylogeny tells life’s story “from the beginning,” giving primacy to the nature of the organism and providing the essential context and polarity needed to understand the significance of evolutionary transitions. Some transitions are more significant than others, reverberating throughout the Tree of Life. These are the milestones of evolution that emerge, spread, and become widely embellished through time. The truly major transitions such as the origin of eukaryotic cells, heterotrophy, photoautotrophy, herbivory, and terrestriality change “the game of life” itself. Such transitions happen rarely, being limited both by the nature of the organism (the information is difficult to achieve, requiring the emergence of novel capacities) and the nature of the conditions (opportunities for selection favoring the transition are rare). But the evolutionary payoff for such transitions can be very large, leaving a lasting impact on the Tree of Life and strong signals for phylogenetic analysis to detect.
