Natural selection is not sensitive enough to small changes to drive evolution.
Even changes so tiny as to seem insignificant to us at first glance can have profound effects on survivability. Who, for instance, would ever think that differences of less than half a millimeter in length and depth in the beak of a finch could spell the difference between survival and starvation? But this is exactly what Peter and Rosemary Grant observed in their famous field studies of "Darwin's finches" on the Galapagos islands. 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)
I am also reminded of one creationist's response to Susumi Ohno's discovery (described in Bakken, n.d.) that a frameshift mutation allowed certain bacteria to produce an enzyme that would metabolize a previously inaccessible food source (an industrial pollutant). The creationist sneered at this mutation, citing the fact that the resultant enzyme worked at "only" 1% the efficiency of other enzymes (other enzymes, incidentally, whose efficiency had been honed by billions of years of evolution); it made absolutely no difference to him that the bacteria now had access to a completely new food source! But to those who do not already have all the answers, it is quite obvious that this little 1% could easily spell the difference between life and death, and that natural selection would not be insensitive to it.
Bakken GS. Creation or Evolution? Berkeley: National Center for Science Education. [Pamphlet]
Weiner J. 1994. The Beak of the Finch: A Story of Evolution in Our Time. New York: Vintage.
Last updated: 21 Mar 2008
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