Here's another old manuscript from the Blog Journals, 2008.
Because it's the world majority blood type, we all know plenty of O's. Let's have a look at their physiologically/anthropologically-driven temperament.
There are two major ways to describe blood type personality: One is its natural expression without respect to society. The other is in terms of its relation to society. There is the O temperament, for instance but then this is tempered by the very fact that O prevails in great numbers; so, with O, you've got "This is how I am", but you also have to deal with O's "And everybody should be as I am", an attitude based less on O temperament than on O's EXPERIENCE that most folks are indeed like himself. We'll see that, in this regard, A tests the waters, to see how many share his own orientation, while B and AB begin with the premise that no one is like themselves: These latter individuals expect to be misunderstood, to be self-contained and stand alone. So, understand that O expects others to see things his/her way, as a "given", and then you're ready to understand other aspects of O personality.
Next step: Anthropology. O began as a hunter and gatherer. O pits himself against nature, bringing all of his resources to bear on making a killing, accomplishing his goal. He tracks his quarry, bringing others on board to assist him. His survival is bound up in projects that have beginnings, middles and ends. He feasts on the proceeds and then goes out to stalk the next Meal, bring down the next foe.
So O likes projects and brings great energy to these, taking for granted that everyone is on board, unless they're prey too. O figures "You're either part of the team or we eat you." This assumption of antagonism on the part of those who don't dance to his tune can be quite stunning to others.
O makes a good leader and a problematic follower. How can mixed society cope with a majority that is leadership-geared ? Answer: O's need spheres of leadership, not necessarily in careers, per se.
And then there's the physical: O's are physically energetic. It's good for them to work out, in relatively short bursts. Just as hunters alternate between slow quiet stalking and climactic pouncing, O's workouts should be short but daily. I think that's akin to their natural anthro-driven rhythm.
Hunting is the ultimate focussed activity; if you're focussed and alert, you eat; if your mind wanders, you starve. So you see a pattern with O: He single-mindedly goes after what he wants till he gets it. After the feast, he's onto something else, with equal intensity. This is why O's do so well with project management. They make one thing happen. Then another. They don't necessarily "work well with others", though. Just as hunters use beaters or a pack of hounds, O's might view their teams as subordinates. A whole team of O's each with his own sphere of authority, is therefore a winner. Otherwise O's can come across as opportunist users. This is an aspect of focussedness that is a social problem for O: Others are used when serving O's ego or career goals or projects, and may be made to feel stepped-on otherwise. O's can even interrupt or fall asleep during others' self-expression. They quite simply are uninterested in others' input unless they can use or usurp it to their own ends. The world is their and only their oyster. They have to train themselves to be more genuinely interested. But if they can at least fake it, that, too, might be an advance for some!
All of this is not to say O's are unlikeable. On the contrary, the world contains its share of adorable O's. Blood type doesn't swallow up or override what makes each individual unique, and that's why I'm treating only of the constitutional medical and anthropologic factors.
Medically speaking, O is flammable. O's suffer from inflammatory diseases. Adding fire to the O rhythm, you find someone who tends to anger and outbursts as opposed to, say, withdrawal or worry. O's act quickly and impulsively, too; thus many an O finds himself backpedalling, apologizing, embarrassed by his hyperreactivity to innocent differentness perceived as threat. Someone's contrary point of view is seen as a lit match and the O is thrilled to burst into flame: Igniting is an addictive high for many an O, an impulse impossible to stifle, a momentary opportunity to express his magnificent furnace. O's can love their own anger. When the social/interpersonal/familial messes to be mopped up in its aftermath are permanent, however, O's might actually consider changing their approach. Dr. D'Adamo is to my mind correct in counseling the rechannelling of O-fire into physical sports/training, rather than, say, some sort of psychotherapy. When O's have had a good sweaty workout in the morning, they're less likely to seek prey to intimidate or attack.
Have a look around at the O's in your circle. And if you're O, it can be fascinating and instructive to understand yourself in these terms. I have to say that the O-Anger connection is among the top 5 teachings that I've noticed have impressed listeners when I speak on bloodtype diet/disease/temperament profiles. Many O's can relate to it, admit to having been distressed by it, and are gratified to find, in Dr. D'Adamo, someone who explains it to them.