>Not all traditional hunter-gatherer groups were exclusively Type O.  For
>example, about three-quarters of the Blackfoot and Blood Indians were Type
>A;  ditto for about 30% of the Navajo.

>From an evolutionary perspective, it makes
>little sense that within a population, in which everyone ate the same foods
>for thousands of years, there would be sub-groups with completely different
>dietary needs; hunting tofu was not an option for the Blackfoot.

One of Daniel Quinn's books (either "Ishmael" or "Story of B," I forget
which) mentions that some of the plains Indians were agricultural for a
time, and they became hunter/gatherers again after they learned from the
Spanish how to use horses.  Maybe that explains the other blood types?