It could easily be psuedoscience. But as even 'proper' scientists are swayed into drawing the conclusions they do thanks to huge bungs from pharmaceutical companies etc (I'm equally cynical, Spangles
), there could just as easily be something to it. The explanation about evolution goes as follows:
Blood Group O was the first blood type to be identified, although how we know this is anyone's guess - we're talking about our hunter-gatherer ancestors who were around in 50,000 B.C! Nevertheless, Dr D'Adamo believes because our type O ancestors survived and thrived on a high-protein, meat-based diet, that's the type of diet blood group Os should follow in the 21st century.
Next came the emergence of blood type A, sometime around 15,000 B.C! By this time, our ancestors' hunter-gathering days were over and instead they started to settle into farming-type communities. The creation of blood type A around this time meant our ancestors did well on a vegetarian-based diet. And again, Dr D'Adamo recommends that blood group A's should today follow a veggie diet.
Blood type B supposedly evolved around 10,000 B.C thanks to our nomadic ancestors. They left their farms and started wandering the land, constantly moving from place to place. Consequently, Dr D'Adamo's theory goes, blood group B's today can get away with eating a varied diet that consists of most foods including meat, dairy, grains and vegetables.
Finally, came blood type AB, which evolved just 1,000 years ago! Dr D'Adamo thinks this blood type helped our ancestors make the transition to modern times. Meaning that people with blood group AB can eat a mixture of the foods suitable for both blood group A and blood group B.
(extract from:
The Blood Group Diet Review)