Why are there "blood types" if all men came from Adam and Eve? It is because all living things undergo mutation. Mutation within the cells, a mutation within DNA, and in various parts of our body. That is the reason for the variations.
Only God does not undergo mutation, according to the Bible. In James 1:17,
"Every good gift and every perfect gift is from above and cometh down from the Father of lights, with whom is no variableness, neither shadow of turning."
The word translated as "variableness" is parallage in Greek. Parallage means transmutation. Only God does not transmute. Only God does not undergo parallage or transmutation. Other living things also mutate, not the only man. This is why there came to be different types of blood.
But there are not many. There are generally four blood types. In the long history of mankind, there are generally four blood types.
"All humans and many other primates can be typed for the ABO blood group. There are four principal types: A, B, AB, and O. There are two antigens and two antibodies that are mostly responsible for the ABO types."
LINK: https://www2.palomar.edu/anthro/blood/ABO_system.htm
There are only four principal types of blood: A, B, AB, and O. And mind you, "O" is the most common. Why "O"? Why is there a dominating type among all humans?
It implies, scientifically speaking, that we all came from one blood.
What the Bible recorded is true. In the Book of Acts 17:26,
"And hath made of one blood all nations of men for to dwell on all the face of the earth, and hath determined the times before appointed, and the bounds of their habitation;"
All nations of men came from one blood. The fact that there are thousands of years that have passed in human history and up to now, there are only four principal blood types, proves that we came only from one blood. The mutation has caused a little change to have now as far as four principal types of blood.
