“The origin of adaptations…is one of the deepest problems in Darwinism. How do novel adaptations arise from small and gradual beginnings?
There is a genus of finches with mandibles that cross over at the tips…called crossbills… The twisted beak allows the bird to pry open closed (pine) cones.
What Benkman and Lindholm did was to uncross the beaks of these birds by trimming the crossed part of the mandibles with an ordinary nail clippers.
The birds with uncrossed bills turned out to be just as good as ever at extracting seeds from dry, open pinecones. Byt they could no longer handle closed cones.
Day by day, as the twist in their beaks grew back, the birds did better and better with more and more recalcitrant cones. After a month, their beaks were completely regrown.
Benkman and Lindholm could measure the value of an adaptation from its very beginnings to its final form.
If crossed mandibles were useful to these birds only when fully formed, then it really would be a puzzle how they could have arisen by natural selection. The cross would have to appear all at once.
It would be the kind of problem before which Darwin felt his theory would “absolutely break down.”
But the finches began to get better at opening pinecones when the cross in their beaks was still too small to be visible to the eye. Even a slight crossing of the mandibles confers a small, incremental benefit, making more and more tightly closed cones accessible….
The press of competition in the woods would have made the novelty of a crossed beak more and more desirable, because it would allow its possessor to eat food n one else could eat; the same competitive pressure would favor each new twist…
Today, however, theere is no profit to a sparrow or bunting in a deformed, twisted bill, because the crossbill niche is taken.”
-The Beak of the Finch
Jonathan Weiner, 1994
Excerpts from pages 180-184, emphasis mine
My Commentary: As convincing as these experimental results are, I still wonder about species such as the Emerald Jewel wasp that rely on precision brain surgery on the host of their larvae to successfully reproduce.