Approaches similar to those described in Sections 8.1 and 8.4 allow some quantitative analysis of the issues affecting the generation and analysis of genealogies but are, in general, restricted to highly idealised situations. The program Genie is designed to model many of these issues by direct simulation, and thus allow quantitative analysis of their implications in more complex situations, inaccessible to other methods. Nevertheless, practical considerations such as computing power requirements limit the population size and number of generations that can reasonably be simulated on a standard high-end desktop machine to the thousands.

It is worth emphasising that, unlike many of the simulations from the literature referred to in the previous chapter, Genie is not explicitly based on coalescent theory. Coalescent-theory-based simulations proceed backwards in time, simulating the death process where j lineages are maintained for a length of time tj, before moving to a state with j — 1 lineages, and repeating until j = 1. Given a specific situation to simulate, i.e. a set of demographic parameters, this process can be completed very rapidly and repeated in order to estimate the probability distribution of the underlying random variable (e.g. the time to the most recent common ancestor) as well as to estimate various point and interval statistics.