Perspective: The pace of modern life: Measuring rates of contemporary microevolution

We evaluate methods for measuring and specifying rates of microevolution in the wild, with particular regard to studies of contemporary, often deemed "rapid," evolution. A considerable amount of ambiguity and inconsistency pe rsists within the field, and we provide a number of suggestions that should improve study design, inference, and clarity of presentation. (1) Some stu dies measure change over time within a population (allochronic) and others measure the difference between two populations that had a common ancestor i n the past (synchronic). Allochronic studies can be used to estimate rates of "evolution," whereas synchronic studies more appropriately estimate rate s of "divergence." Rates of divergence may range from a small fraction to m any times the actual evolutionary rates in the component populations. (2) S ome studies measure change using individuals captured from the wild, wherea s others measure differences after rearing in a common environment. The fir st type of study can be used to specify "phenotypic" rates and the later "g enetic" rates. (3) The most commonly used evolutionary rate metric, the dar win, has a number of theoretical shortcomings. Studies of microevolution wo uld benefit from specifying rates in standard deviations per generation, th e haldane. (4) Evolutionary rates are typically specified without an indica tion of their precision. Readily available methods for specifying confidenc e intervals and statistical significance (regression, bootstrapping, random ization) should be implemented. (5) Microevolutionists should strive to acc umulate time series, which can reveal temporal shifts in the rate of evolut ion and can be used to identify evolutionary patterns. (6) Evolutionary rat es provide a convenient way to compare the tempo of evolution across studie s, traits, taxa, and time scales, but such comparisons are subject to varyi ng degrees of confidence. Comparisons across different time scales are part icularly tenuous. (7) A number of multivariate rate measures exist, but con siderable theoretical development is required before their utility can be d etermined. We encourage the continued investigation of evolutionary rates b ecause the information they provide is relevant to a wide range of theoreti cal and practical issues.