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?
you won’t find how many had children by finding Adam and Eve, you’ll find the first antecessor of all. maybe you’ll find correlated things.
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.