Assertion 4.27: Natural selection is not sensitive enough to small changes to drive evolution.
Analysis:
Even minor changes can have profound effects on survivability, as illustrated by an episode in the famous field studies of "Darwin's finches" by Peter and Rosemary Grant. When the Grants examined the data for the medium ground finch Geospiza fortis on the Galapagos isle Daphne Major during a terrible famine from March 1976 to December 1977, they found out just how sensitive natural selection could be:
The average fortis beak before the drought was 10.68 millimeters long and 9.42 deep. The average beak of the fortis that survived the drought was 11.07 millimeters long and 9.96 deep. Variations too small to see with the naked eye helped make the difference between life and death. The mills of God grind exceedingly small. (Weiner 1994:78)
References
Weiner J. 1994. The Beak of the Finch: A Story of Evolution in Our Time. New York: Vintage.