Chapter 9 presents an empirical case for the importance of mutational biases, based on studies of adaptation traced to the molecular level. Where Chapter 8 identified a variational cause of bias that does not depend on neutral evolution, absolute constraints, or high mutation rates, this chapter focuses on how quantitative biases in ordinary nucleotide mutations influence adaptive evolution. It uses published studies of parallel adaptation in nature and in the laboratory. The natural studies include both (1) cases of recent local adaptation, e.g., evolution of resistance to insecticides and herbicides, and (2) cases of fixed changes, e.g., altitude adaptation via changes in hemoglobins, spectral tuning of photoreceptors used in color vision, and so on. The results indicate that the kinds of changes that happen most often in adaptation are the kinds favored by simple biases in mutation, e.g., transition-transversion bias.
Color vision of the coelacanth (Latimeria chalumnae) and adaptive evolution of rhodopsin (RH1) and rhodopsin-like (RH2) pigments