The architecture was designed by humans; the weights were not. The harness itself is not the agent; it is an interface with the LLM weights that allow those weights to do useful things. The magic of LLMs comes from the weights, the very part of the system that is not written code.

Gradient descent/backpropogation is similar to evolution, in that both are optimization processes that over time discover better more efficient solutions to problems. The difference is that evolution is blind, and can only make progress via random mutation and natural and sexual selection, whereas backpropagation allows much more rapid discovery because it is directed