If the origin of life is not part of natural selection theory it is certainly germane thus it was not to elucidate natural selection or evolution that Miller cooked up a goo but rather to search for life's origin.
No life, no selection. No life, no evolution. Without dealing with the origin life there's point to either theory
anymore than a historian can study how a building was built and remodeled without considering how it started to be built.
read “no point”