Question 1

Why do humans have different blood types?

Accepted Answer

Blood types persist because each one offers protection against certain ancient diseases while leaving the body more vulnerable to others. Type O resists severe malaria but raises cholera and ulcer risk, for example. These trade-offs kept all types in balance rather than letting one dominate.

Question 2

Why can the wrong blood type kill you?

Accepted Answer

Your immune system makes pre-formed antibodies against the ABO antigens you lack. A mismatched transfusion triggers these antibodies to attack the incoming cells, causing them to clump and rupture, which can lead to kidney failure, shock, and death within minutes.

Question 3

What makes type O the universal donor?

Accepted Answer

Type O red cells carry neither the A nor the B antigen, so there is nothing on their surface for another person's antibodies to attack. That makes type O blood broadly safe to give to recipients of most other ABO blood groups.

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The Letters Hidden in Your Blood