Given what we know about genetics, we can confirm that the case described in the question will be a result of a De Novo mutation.
A De Novo mutation is referred to as the most severe mutation type. This is a mutation that occurs even before embryonic development has commenced. They are usually the result of mutations in the DNA of the germ cells before being fertilized.
These mutations are responsible for a variety of disabilities and can target a wide array of genes to cause these effects.
Adaptive radiation is an evolutionary activity which creates several new species out of a single specie. Darwin embraces this philosophy that the finches evolve from an ancestral finch by adapting to the different environment.
