They used coalescent analyses of three independent loci to distinguish between these two hypotheses. A coalescent tree traces the descent of alleles of a gene in a population. The expected allele frequency spectrum may be calculated using either a coalescent or diffusion approach. For example, coalescent theory is used to fit data to models of idealised populations. In the coalescent model of population genetics each genetic locus has its own unique history. Coalescent theory seeks to estimate the expectation of this time period and its variance. The coalescent processes in different populations are different. This estimate is based on coalescent theory. The process is also called the Censored Coalescent. He is a specialist in applied probability and has made contributions to coalescent theory. In modeling the coalescent process, time is usually considered to flow backwards from the present. The point where two branches meet indicates a coalescent event. Additionally, fixation rates can be modeled using coalescent trees. "Coalescent" was nominated for the Arthur C. Clarke Award in 2004.