[csense]

natural selection....which can be observed, tested, etc...

Finally, someone who may be able to answer my question. 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.

[kpp_kpp]

is natural selection not just a term that takes all of those into account?

[Tamar1973]

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.

Processes like mutation, drift, recombination, and heredity contribute to natural selection because they affect how an organism co-exists with its own environment.

[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).