As the number of whole genomes available for study increases, so also does the opportunity to find unsuspected features hidden within our genetic code. One such feature allows for an estimate of the Human Mutation Rate in human chromosomes to be made. A NUMT is a small fragment of the mitochondrial DNA that enters the nucleus of a cell, gets captured by a chromosome and thereafter passed on from generation to generation. Over the millions of years of evolution, this unexpected phenomenon has happened many times. But it is usually very difficult to be able to say just when a NUMT might have been created. However, this paper presents evidence to show that for one particular NUMT the date of formation was around 29 million ago, which places the event in the Early Oligocene; when our ancestors were small monkey-like creatures. So now all of us carry this NUMT in each of our cells as do Old World Monkeys, the Great Apes and our nearest relations, the Chimpanzees. The estimate of the Human Mutation obtained by the method outlined here gives a value which is higher than has been generally found; but this new value perhaps only applies to non-coding regions of the Human genome where there is little, if any, selection pressure against new mutations.