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.
Yes, you'd need much more detailed genealogical information. There's tons of modern genealogies, of course, but how useful are those outside the modern era?
His book was the second sentence in the page. :)