Before revision:  In this paper, we introduce a theoretical framework that provides a synthetic perspective to explain why there exists extreme diversity across layers and within levels.
After revision:  In this paper, we introduce a theoretical framework consisting of layers of control loops with components having diverse speeds and accuracies within each physical level, such as nerve bundles containing axons with a wide range of sizes. Our model explains why the errors from two control loops -- one fast but inaccurate reflexive layer that corrects for bumps, and a planning layer that is slow but accurate -- are additive, and within levels.