Can Pareto Optimality Be Evidence of Life?

Biological evolution confronts situations in which the modification of a trait to improve the performance of one function may diminish the performance of another. Similar trade-offs occur in economics and engineering, where they are evaluated with the concept of Pareto optimality. "Pareto optimal" solutions are solutions such that performance cannot be improved for any task without sacrificing performance for another task. Solutions outside the Pareto optimal set are likely to be uncompetitive in that they could be improved without negative consequences. Biologists have argued that optimization for multiple biological functions restricts the variety of evolutionarily stable phenotypes to a Pareto set within traitspace, while promoting diversity within this set. Here, we consider whether evidence for such optimality could serve as evidence of life in astrobiology. We propose that objects whose properties lie demonstrably within a region constrained by trade-offs between biologically relevant functions are more likely to be biogenic; examples discussed here include bacterial morphology, mycelial networks, and the selection of molecules. Conversely, objects with comparable characteristics to known forms of life that exist outside the relevant Pareto set are less likely to be biological. We conclude that the detection of Pareto optimality may disclose functionality and, hence, biogenicity in unfamiliar materials.