Cann, Stoneking, and Wilson estimated the mutation rate by looking at the mtDNA of groups of people whose ancestors migrated to areas at known times. One group was Australian aborigines, whose ancestors moved to the island-continent a then-calculated 30,000 years ago.
[4] Since the three then knew how long it took for that group's mtDNA to diverge as well as how much it diverged, they determined the mutation rate. Using this rate, they determined that the most recent common ancestor lived 140,000 to 290,000 years ago (which they roughly averaged to 200,000 years ago). That was back in 1987. Since then, researchers have updated the estimate to 120,000 to 150,000 years ago. However, the margin for error for this estimate and the previous one are significant—when all of the variables are taken into account, the current range is more like 50,000 to 500,000.