That's a good response. But do you see the difference between the fact of gravity and the "fact" of Darwinian natural selection?
One has been observed, indeed is the very nature of reality. The other has not. Despite years of study, only adaptation within species has been oberved.
Moreover there is an ongoing debate within the scientific commuinty over the mechanism - Darwinian-flavored natural selection vs. punctuated equilibrium. Linneaus (who gave us the categorization system of genus-phylum-species-subspecies) held fervently to the fixity of the species because of the inability (or, sever limitations in the case of donkeys and horses) of interspecial breeding. We now know a dog has 78 chromosomes, for example, while a fox only has 37. They cannot breed (eliminating macroevolution), and deformed outcasts are usually killed by siblings (eliminating "hopeful monster" theory).
You will no doubt recall that Darwin himself, at the end of Origin of Species, expressed his hope that the fossil record would, in the coming years, fill out to provide smooth transitions from species to species. He even stated his theory depended upon this (see last chapter of Origin). This has not happened. For these reasons, it is not honest to call Darwinian evolution a fact.
Thanks for your comments which I think are good as well
as provocative. Perhaps the problem lies in your reference
to "observation" and perhaps my example is too oversimplified. There are many realities that cannot simply
be "observed" and quantified by simple empirical observation. The earth is believed to be about four and a
half billion years old. There are many things known to
be scientifically true that cannot have been observed, e.g.
the tectonic shift of the continents and many other
such geological phenomena. Einstein posited that the only
absolute in the universe is the speed of light and as that
speed is approached time diminishes and mass increases.
Obviously, this cannot be "observed" but it can be confirmed mathematically. You mentioned the "difference
between the fact of gravity and the fact of Darwinian
Natural Selection." I do see the difference but I think
that difference has to do with the matter of "observation"
as I sketched above. Of course, neither evolution nor
any other phenomenon which occurs over millenia is completly comprehended or explained to the fullest extent
possible. Electromagnetism is said to be one of the four
central forces of the universe - yet there is much we don't
know about it and more that we learn as time progresses.
This is why there is and must be "debate within the
scientific community." One of the points I made elsewhere
is that evolution has been verified by experiments with
such things viruses and certain bacterial life where time
ceases to impede "observation." I think one of the most frustrating things (to me) about a discussion of evolution
is how emotional, irrational, and nearly unhinged some
people become. If we all heard that some aspect of quantum
physics relating to quarks had been verified - it would
be met by these people with a big yawn. But assert that
evolution is true then LOOK OUT! Perhaps this still
unsettles certain religious beliefs. I accept evolution
and it is no threat whatsoever to my religious faith.
I'd like to hear back from you -- and congratulations
for an intelligent, rational response. It's much appreciated.