Coalescent theory is a probabilistic framework

Wessen-Simulating-human-origin-evo.pdf Simulating Human Origins and Evolution by Ken Wessen (2005) pp 13: The study of a population is generally retrospective in nature, starting with a sample from an existing population and then attempting to describe the observed features in terms of the population’s prior evolution. Results are then generalised from the sample to the entire population. Coalescent theory (Kingman, 1982b; Hudson, 1990) provides a probabilistic framework perfectly suited to this approach, and has therefore become an extremely important tool in population genetics over the past 20 years. In brief, coalescent theory describes the merging of lineages from a sample of a population as one goes backwards in time, to the point where only a single lineage remains, i.e. the common ancestor. It is particularly well suited to molecular data, and although the usual formulation is based on the neutral model (Kimura, 1968) and a single, randomly mating population of constant size, extensions to cover recombination (Hudson, 1983), population growth (Kuhner et al., 1998), population subdivision (Hudson, 1990; Donnelly and Tavaré, 1995) and selection (Neuhauser and Krone, 1997) are well developed and are the subject of much ongoing research. A good review may be found in Fu and Li (1999).