If all of humanity descended from Adam and Eve—as the Bible teaches—how is it possible that people have different blood types today?
An answer comes from basic genetics. Unlike other traits that are controlled by multiple genes, the A, B, and O blood types are controlled by a single gene. However, this gene comes in three slightly different versions, known as alleles, and that is why we have these three possible major blood types.
When God created Adam and Eve, He could have created them with great genetic variety. This means Adam and Eve could have possessed all three alleles between them. However, blood type O appears to be due to a mutated or damaged version of blood type A allele, which suggests it arose later in human history. This means Adam and Eve would only need to possess the A and B alleles between them. So the origin of blood types is consistent with the Bible’s history.