The cumulative distribution function (CDF) for the time to the most recent common ancestor, $tmrca$⁠, for a sample of size s = 2 or 8. Time is measured in the coalescent unit of 2N generations or $2τ/θ$ in the notation of this article. The CDF gives the probability that the whole sample coalesces within the given time. For S = 2, t is exponential with mean 1 and CDF $1−e−t$⁠, whereas for S = 8, the CDF is generated by coalescent simulation (with 10⁷ replicates).