So if the average bear can observe that DNA base pairs change at the rate of say a few hundred per generation on average, why can't he make the same straight line extrapolation to lead to the several million pairs difference seen between closely related species?
:: Because the changes in base pairs don't necessarily add information. They can just as easily subtract or move sideways.
So what? Evolution doesn't necessarily add information either. It can go "backwards" or "sideways", whatever that means.