Ecological Origins of Complex Multicellularity in a Digital Model

Evolution by natural selection occurs when organisms more adept at living and reproducing in their current environment increase in frequency over time. However, organisms are not just passive inhabitants of their environment — they are part of it, and can directly influence each others’ survival and reproduction. Organisms can also remodel their environment, creating further opportunities to shape biotic and abiotic selection, and thus which traits are beneficial or deleterious (i.e., niche construction). While studying the evolution of multicellularity using populations of event-driven multi-threaded replicating computer programs (i.e., digital organisms), we observed through detailed case study analysis and evolutionary replay experiments that selection imposed by organisms on one another can lead to the evolution of distinct complex multicellular life histories. Surprisingly, organisms with complex genetic programs were not inherently more fit; instead they had collectively reshaped selection. This effect helped stabilize evolved complexity, where evolution of multi-stage developmental patterns “locked in” selection for organisms with similarly coordinated developmental programs. These findings show how biotic selection can act as a powerful complexity ratchet, and concretely demonstrate a possibly critical role of eco-evolutionary feedback in early evolution of biological multicellularity.

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