don’t you think early man would have taken saturday and sunday off though? from walking a mile i mean? so that would ad some time.
Yeah, but which days are Saturdays and Sundays. I'm betting they lost the calendar along the way.
You could probably add a few years for stopping for childbirth, burials, fights with mastodons and saber tooth tigers, Christmas and Easter, etc. So, let's say it took a bit longer. :)