Something, Darwin realized, was very wrong. Why should there be so many unique species on these similar islands? … Perhaps the finches had not been created in their current form. Perhaps they had evolved. 
It wasn’t that the evidence revealed how evolution could possibly create a finch; rather, the evidence was showing that they wouldn’t have been created. For if the finches on those different islands were different species, as Darwin anticipated in a famous notebook entry, it “would undermine the stability of species.”
Evolutionary metaphysics run deep and drive the science to where it shouldn’t go. This brings us back to those finches which not only provide powerful metaphysical arguments but also rather silly scientific arguments.
What is fascinating is that evolutionists believe they have found yet more powerful evidence for their idea. It is another example of how theology drives the science in evolutionary thought.
The story is that in 1977 a drought in the Galapagos Islands left a severe shortage of small seeds that G. fortis fed on. The majority of the population died off leaving only the larger birds with larger beaks which could feed off of larger seeds.
Naturally subsequent generations of G. fortis had larger beaks. As the years passed the population returned toward its pre drought state with more of the smaller beaks, but for a few generations the drought had caused a significant change in the population.
Amazingly evolutionists advertise this as powerful evidence of evolution by natural selection occurring before our very eyes. As Coyne concludes in his book Why Evolution is True:
This is a staggering rate of evolutionary change—far larger than anything we see in the fossil record. … Everything we require of evolution by natural selection was amply documented by the Grants in other studies: individuals in the original population varied in beak depth, a large proportion of that variation was genetic, and individuals with different beaks left different numbers of off-spring in the predicted direction. 
Everything we require? A drought occurred and the majority of a bird population died off leaving only the larger birds which could access different food sources. And that’s powerful evidence of evolution? You’re joking right? This reasoning is absurd.
The variation was already present in the finch population before the drought occurred. That’s why the change could happen so fast. The average beak size increased, as evolutionists continue to point out, because the vast majority of the smaller birds died off, not because any new design was created. As usual, natural selection merely killed off the unfit designs.
Over the years evolutionists have presented a great many evidences for their theory. But while the metaphysics make for a powerful and compelling argument, the science is inevitably weak or flawed. Darwin’s finches are no different.