[Sofa King]

"If natural selection can be observed and tested, what physical event or process, does natural selection explain, that isn't already explained by mutation, drift, recombination, and heredity."

Natural selection is a process by which beneficial mutations and recombinations are kept and inherited into future generations, and harmful ones are rejected. Natural selection uses those three processes, and eventually a beneficial mutation/recombination will be shared by the entire population (drift).

[csense]

Natural selection is a process by which beneficial mutations and recombinations are kept and inherited into future generations, and harmful ones are rejected. Natural selection uses those three processes, and eventually a beneficial mutation/recombination will be shared by the entire population.

Well, if natural selection can describe any given genetic state, of any given population of organisms, then I don't see how it is either testable or falsifiable, let alone useful in a scientific theory.