People with type O-blood are considered “universal donors” because their blood doesn’t have any antigens or proteins, meaning anybody’s body will be able to accept it in an emergency.
But why are there different blood types? Researchers don’t fully know, but factors such as where someone’s ancestors are from and past infections which spurred protective mutations in the blood may have contributed to the diversity, according to Dr. Douglas Guggenheim, a hematologist with Penn Medicine. People with type O blood may get sicker with cholera, for example, while people with type A or B blood may be more likely to experience blood clotting issues. While our blood can’t keep up with the different biological or viral threats going around in real time, it may reflect what’s happened in the past.
“In short, it’s almost like the body has evolved around its environment in order to protect it as best as possible,” Guggenheim says.
