I think its possible. Human body quikly adapts to new way of life. I wonder if A group is more prevailent among people who live or had ancestors who lived in areas where vegetable growing was important and B group people come from historicaly dairy regions (cheese, sirov burek, etc.) and so on.

Yeah, but it's very flawed. First blood type isn't O but it's A… it's A blood group that humans share with primates as monkeys and it's the oldest one…and secondly, never did people live only on agrarian, because agrarian products where at the time just an addition to the overall diet… i don't believe anywhere did Europeans stopped eating meat just because they had wheat and stuff :/

imo it's a fail, thought i'm still interested in what others think…and for example then Italians would be heavilly blood type A if it was truth since during Roman times they were heavily on agrarian diet… while English, Scandianvians and most Slavs and such would heavily be blood type O (according to the blood type diet theory) since they used to hunt more and eat meat rather than seed and crop, but the reallity is bloodtype A is a very common group in Scandinavia for example. Most of Europeans belong to A bloodtype  ::)