Watson, Richard A., and Jordan B. Pollack. “The Major Evolutionary Transitions, Symbiotic Composition, and Implications for Evolvability.” (2001).
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Several of The Major Transitions in evolutionary history, such as the symbiogenic origin of eukaryotes from prokaryotes, share the feature that existing entities became the components of composite entities at a higher level of organisation. This composition of pre-adapted extant entities into a new whole is a fundamentally different source of variation from the gradual accumulation of small random variations, and it has some interesting consequences for issues of evolvabilit y. Intuitively, the pre-adaptation of sets of features in reproductively independent specialists suggests a form of ‘ divide and conquer’ decomposition of the adaptive problem. Moreover, the compositions resulting from one level may become the components for compositions at the next level, thus scaling-up the variation mechanism. In this paper we explore and develop these concepts using a simple abstract model of symbiotic composition to examine its impact on evolvabilit y. To exempli fy the adaptive capacity of the composition model, we employ a scale-invariant fitness landscape exhibiting significant ruggedness at all scales. Whilst innovation by mutation and by conventional evolutionary algorithms becomes increasingly more diff icult as evolution continues in this problem, innovation by composition is not impeded as it discovers and assembles component entities through successive hierarchical levels.