NOTE 15N: This difference in the mismatch distribution has been used as a way to distinguish alternative population histories using mitochondrial DNA. However, in any one realization from a population of constant size, the distribution is dominated by when the oldest pair of lineages coalesce and is highly random. The method is not as accurate as the above comparison of the distribution over many independent realizations (see Fig. P15.6B and Fig. 25.24). Moreover, accuracy is not much improved by taking larger samples: The main randomness is in when the MRCA lived.