my argument is not a strawman. to call it such is to cheapen reasonable discussion. i chose an example to illustrate the inherent problem with applying the scientific method to macro-evolution.
if you prefer a narrower focus, then please devise an experiment where we can see one species evolve into another species. i’ll define species as organisms sufficiently changed as to no longer be able to interbreed successfully.
In fact, such simple artificial speciation has been observed in bacteria and fruit flies.
But be careful about that definition of the word "speciation", since in normal scientific usage, two species of the same genus do not naturally interbreed, though may still be forced to in captivity.
It's not until we reach separate genera in the same family (i.e., Indian & African elephants) that interbreeding becomes biologically impossible.
My point is: difficulty in interbreeding is a sliding scale, from easy-breeds & varieties, up to impossible-genera.
Within that sliding scale, small changes in DNA can make big differences in interbreed-ability.
One of the most interesting examples is human races (breeds) which are genetically 99.9% identical and which all interbreed happily.
But now recently we've learned that the old Neanderthals were just 99.5% identical DNA, and did interbreed, occasionally, 50,000 & 100,000 years ago.
So they are no longer a separate species, just another human sub-species.
By sharp contrast, chimpanzees are circa 96% identical to human DNA, and biologically incapable of interbreeding.
Bottom line: speciation begins whenever two populations are separated and it accumulates, generation after generation, until separated sub-species can no longer interbreed, making them different species.