Mutation, specialization, and hypersensitivity in highly optimized tolerance.

We introduce a model of evolution in which competing organisms are represented by percolation lattice models. Fitness is based on the number of occupied sites remaining after removing a cluster connected to a randomly selected site. High-fitness individuals arising through mutation and selection must trade off density versus robustness to loss, and are characterized by cellular barrier patterns that prevent large cascading losses to common disturbances. This model shows that Highly Optimized Tolerance (HOT), which links complexity to robustness in designed systems, arises naturally through Darwinian mechanisms. Although the model is a severe abstraction of biology, it produces a surprisingly wide variety of micro- and macroevolutionary features strikingly similar to real biological evolution.