Question concerning evolution

This is where the number of years you were asking about comes from. It's nothing directly calculated from the DNA; and the authors don't put any number on it. All they're saying is that humans have a similar pattern of diversity to other species, implying a similarity in population history. Journalists are then looking up estimates for the origins of Homo sapiens (50,000, 100,000, 200,000 years) and extrapolating that most species are as old as whichever estimate they picked.

What are we actually looking at? We're looking at how long the mitochondrial genome has had to accumulate neutral variations - the more neutral variations, the longer it is since we can trace a populations mitochondrial diversity back to a small group of individuals. Is that the origin of a species?

So we calculate based on observations and understanding of the mechanisms how many mitochondrial mutations there are per generation. When we're only examining a 100 generations, the error margin is likely to be high. When we're examining 10,000 generations (ie., for humans about 200,000 years) the error margins are smaller. The more trials, the smaller the error margin.As ever, there are always complications and confounding factors, but that's the gist of it.