"No new genetic material was necessary for the change in manifestation -- both the moths and the dogs are fully capable of mixing back to a more "original" appearance by interbreeding"

That's the point I was making. Speciation isn't a 'thing'- you can't draw a line and say 'now it's a new species'. It's a continuum. It's only when varieties have drifted apart so far that the differences are obvious that we call them different species. This usually happens because a population gets split, perhaps (a hypothetical example) by a climatic change that puts a desert between two groups of deer. They can't interbreed simply because they never meet: and as the ecosystems gradually diverge, adaptive variation accumulates, and different species result.

There's very little 'new' genetic material involved; I'm sure you know the cliche about humans sharing 99% or whatever the figure is of our DNA with chimps, and 83% with fruit flies, and about 60% with bacteria, even significant amounts with plants. You wouldn't claim that we were 'merely' variations of lugworms on that basis?

As for humans, yes, we are all one species. One race, the human race. It's quite possible that speciation would have occurred eventually had we remained in separate groups (say Eurasia, the Americas, Australia) for a few tens or hundreds of thousands of years more, but the variation that did occur in the 40000 years ors so since the human diaspora was fairly minor. Not really surprising; some species remain stable for millions of years. Homo sapiens(ish) seems to be adapted for many different habitats- perhaps because our main adaptation is to change the habitat to suit ourselves.