Sequence Convergence and Functional Adaptation of Stomach Lysozymes from Foregut Fermenters

Until about 1974, a basic assumption guiding investigations on the molecular basis of adaptive evolution was that amino acid replacements in proteins are the basis for the observed differences among individuals, populations, and species. However, quantitative studies of protein evolution, considered in relation to knowledge of taxonomic distance, led Wilson and co-workers (1977) to question this assumption. They hypothesized that regulatory mutations were responsible for most observed variations in anatomy, physiology, and lifestyle of organisms. There is considerable evidence that the concentrations of well-known proteins vary greatly from one species to another, but the adaptive significance of these differences is often unclear.