I'm not sure what you mean. While they might come from common origins there are predictable rates of mutation in genes over time, and we can use them to track populations. So by comparing which mutations are present where surely you can get a rough idea of what percentage of the population was reproducing?
Edit: Gwern's post above gives a better answer.
There's an idea I've seen a number of times that 80% of women have had descendants, but only 40% of men. A little research tracked it back to this, but the speech doesn't have a cite and I haven't found a source.
The reproduction rates for men and women (possibly for the whole history of the species) seems like the sort of thing which could be found out, but I'd like more solid information.