Darwin's Doubt: The Explosive Origin of Animal Life and the Case for Intelligent Design

by Stephen C. Meyer

Whereas Maynard Smith saw the need for multiple coordinated mutations as a potential problem, one that ultimately needn’t trouble evolutionary biologists, Behe and Snoke argued that evolutionary biologists do need to worry about it, and they quantified its severity. Behe and Snoke first noted that many proteins, as a condition of their function, require unique combinations of amino acids interacting in a coordinated way. For example, ligand binding sites on proteins—places where small molecules bind to large proteins to form larger functional complexes—typically require a combination of several amino acids. Behe and Snoke argued that in such cases the combinations of amino acids would have to arise in a coordinated fashion since the capacity for ligand binding depends on all the necessary amino acids being present together. In support of this inference, they cited an authoritative textbook, Molecular Evolution, by University of Chicago evolutionary biologist Wen-Hsiung Li. In it, Li notes that evolving ligand binding capacity in proteins such as hemoglobin may require “many mutational steps,”21 even though the first steps on the way to building such capacity would confer no selective advantage. As Li explains, “Acquiring a new function may require many mutational steps, and a point that needs emphasis is that the early steps might have been selectively neutral [non-advantageous] because the new function might not be manifested until a certain number of steps had already oc...