Before revision: Maynard Smith and Szathm\'ary's book, The Major Transitions in Evolution, describes eight major events in the evolution of life on Earth and identifies a common theme that unites these events. In each event, smaller entities came together to form larger entities, which can be described as symbiosis or cooperation. Here we present a computational simulation of evolving entities that includes symbiosis with shifting levels of selection.
After revision: We present a computational simulation of evolving entities that includes symbiosis with shifting levels of selection.