Adaptive Landscapes, Evolution, and the Fossil Record

Abstract

Fitness and adaptive landscapes have theoretical limitations, but they have played a valuable role in integrating population genetics and macroevolution. Sewall Wright introduced fitness landscapes in 1931 to describe the relationship between genotypes and fitness, and George G. Simpson modified and popularized the concept of landscapes in evolutionary biology in 1944 as adaptive landscapes to illustrate the evolutionary response of fossil lineages to natural selection. Patterns of sediment and fossil accumulation impose practical limitations on the use of adaptive landscapes to analyze fossil data. Phenotypic evolution can occur too rapidly to resolve in the stratigraphic record, hindering observation of movement of lineages upward on an adaptive peak. Use of the null hypothesis of a random phenotypic walk through time (i.e., genetic drift) to test for adaptation in the trajectory of change in fossil lineages has consistently led to rejection of adaptation, but recent methods, including a maximum likelihood procedure for individual lineages and simultaneous analysis of multiple species and traits, indicate that fossil lineages have ascended adaptive peaks and remained at their summits as they shift position through time. Recognition of the limits to temporal resolution in fossil lineages provide guidance for the selection of fossil lineages to study, and development of new statistical tools have enhanced the value of adaptive landscapes to analyze the fossil record.