But since no one has ever witnessed the crossing of one species to a new one, or succeeded in creating a new species, I think it is not reasonable (ie. unscientific) to insist that conclusion can't be wrong. I don't think that is necessarily true even if such observations are very rare.
This is the first example of speciation that scientists have been able to observe directly in the field.
Researchers followed the entire population of finches on a tiny Galapagos island called Daphne Major, for many years, and so they were able to watch the speciation in progress. --- This example probably gives an insight into the reasons that such observations are rare. Observers have to be lucky enough to be in the right place at the right time and duration for the observations to take place. A lifetime is often not long enough.
