Hi Wally, 
Sure, I make some assumptions there, but they don't take into account that the age of female puberty is declining every decade, from about 16.5 years of age in the 19th Century to today's levels of about 13 years and with outliers as young as 8 or 9 years old.  I wonder what the age of menstruation onset was among HG females? As menstruation and fertility doesn't begin until sufficient body fat is accumulated, and fertility can be interrupted by famine and/or being extremely active. 

One reason that modern humans don't wait that long between children is that breast feeding doesn't usually continue for that long..... usually about 6 months. 

I am pleased that you found the analysis  interesting. 

Best Wishes, 
Ron 
 

-----Original Message-----

Thanks for the read Geoff. Interesting analysis. 

I have reservations, though. Quite a few very loose assumptions made. I'm not so sure about the time lag between "litters". Modern humans certainly don't wait that long between kids. Doesn't mean that's always been the case, though.

http://paleodiet.com/life-expectancy.htm