Question

Why do humans have different blood types? And why is O a generic blood?

Answer 1

The different blood groups are because of different surface protein markers on the blood cells. Type O- has no marker and hence is the least reactive antigenically.

Explanation:

There is no clear scientific reason for the emergence or existence of the separate blood types among humans, though one theory is that they developed along the evolutionary pathway as a result of mutations.

Groups like A, B, and AB as well as the Rh+ sub-types have unique protein markers on the cell surface that enable them to be so typed or grouped. The absence of these markers distinguishes the O- group which is the least antigenically reactive and hence the type which can be transfused into any person.