Acetio | Blogma

On this page about Modern Human Variation is a link to this page about the Distribution of Blood Types with the following opening line:

"Blood provides an ideal opportunity for the study of human variation without cultural prejudice. It can be easily classified for many different genetically inherited blood typing systems. Also significant is the fact that we rarely take blood types into consideration in selecting mates. In addition, few people know their own type today and no one did a century ago. As a result, differences in blood type frequencies around the world are most likely due to other factors than social discrimination. Contemporary Japan is somewhat of an exception since there are popular Japanese stereotypes about people with different blood types. This could affect choice in marriage partners for some Japanese."

The maps on that page show the distribution of blood types in a way that seems to largely match cultural differences.

The map above is a composite I made of the distribution maps for types 'A', 'B', and 'O' blood. Notice how South America seems to be the most distinctive area in the world.