This is by no means an all-or-nothing selection (as the impression is sometimes given). Rather, the alleles are retained.
They are not, per the National Academy of Sciences, a “particularly convincing example for speciation.”
Scientific data are followed by the myth: “Finch beak morphology observed on the Galápagos Islands was used by Darwin to formulate his theory of evolution.”
How could the authors suddenly do this? Some of the following points may be considered.
In a series of posts starting today, I offer some notes on the question of whether macroevolution is happening on the Galápagos Islands.