Individual fitness, an individual’s lifetime contribution of offspring to the next generation, is a key metric for evolutionary adaptation and for population growth. It is straightforward, if time-consuming, to record the components of fitness, survival and the stages of reproduction. Statistical analysis of such data, however, has been problematic because of the compound nature of the distribution of fitness in a population. To enable rigorous statistical analysis of fitness, aster modeling has been developed through close collaboration with Dr. Charles Geyer, School of Statistics, University of Minnesota. Aster capabilities now include estimation and comparison of the mean fitness of study populations, phenotypic selection analysis, random effects models for estimating genetic components of variance, and estimation of population growth rate. Geyer maintains a website that displays all matters aster, including technical reports and tutorials, as well as all our papers about aster and applying it to address evolutionary questions.