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PDF (.98 MB)
Pages 357-363
First published 2 July 2012

The Minimal Complexity of Adapting Agents Increases with Fitness

Nikhil J Joshi, Giulio Tononi, Christof Koch


What is the relationship between the complexity and the fitness of evolved organisms, whether natural or artificial? It has been asserted, primarily based on empirical evidence, that the complexity of plants and animals increases as their fitness within a particular environment increases via evolution by natural selection (Bonner, 1988; McShea, 1996; Adami et al., 2000). We here derive an analytical relationship between these two quantities within an information-theoretical framework, showing that under certain conditions, complexity is a monotonically increasing function of fitness. We also simulate the adaptation of brains of digital organisms living in mazes and whose connectome evolves over 10,000s of generations in a stationary environment. We compute their circuit complexity, using an entropy-based measure (Balduzzi and Tononi, 2008). We find that their minimal complexity increases with their fitness, in line with our analytical derivation.