>I would count 20 years, possibly less, as a generation during >most of that time, which would push it to 500 generations That's what I've always intuitively thought, too. However, I say 300 because all of the material I've read that gives the '10,000-year total generations for humans' figure reports it roughly as such, and I just assumed that there was an underlying mechanism (mathematical or otherwise) beyond my immediate grasp that lengthened the supposed period between generations, and never bothered to investigate for details.