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Blood types have deep roots: ABO system may date back 20 million years or more.

Chimps, gibbons and other primates are not just humans' evolutionary cousins; a new analysis suggests they are also blood brothers. Blood types found in people today evolved at least 20 million years ago in a common ancestor of humans and other primates, new research suggests.

The analysis deepens a mystery surrounding the evolutionary history of the ABO blood system, and should prompt further research into why the different blood groups have persisted over time, Laure Segurel of the University of Chicago and colleagues report November 6 in the Proceedings of the National Academy of Sciences.

"Their evidence is rather convincing that this is a shared, very old capability that has remained throughout the divergence of the species," says physician and transfusion specialist Martin Olsson of Lund University in Sweden.

Different forms of a single blood type gene determine what kinds of molecules sit on your red blood cells: type A molecules, type B molecules, A and B together, or no intact surface molecules in the case of type O.

The A, B and O versions of the gene differ only slightly, and scientists have debated two scenarios to explain their evolution. One posits that the A version of the gene existed long ago, and the B and/or O versions later cropped up independently in several species (including humans, gorillas, baboons and chimps). Alternatively, all of those species may have inherited the A and B types from a single ancestor.

Researchers led by Segurel looked at a particular stretch of DNA in the blood type gene in humans, bonobos, chimpanzees, gorillas, orangutans, gibbons and several species of monkey. Then the scientists compared that stretch of DNA across species on the primate family tree. The pattern they saw suggests that the A and B blood groups were around at least 20 million years ago, probably as far back as the common ancestor of humans and Old World monkeys.

Exactly why evolution would favor a mix of blood types in so many species is a mystery. Depending on blood type, people are more or less susceptible to particular pathogens. Type O people, for example, are more susceptible to cholera and plague, while people with type A are more susceptible to smallpox. Blood group diversity may have been maintained for so long because each version was immunologically advantageous in certain times and places.

"That diversity may have led to protection against whatever might come your way," says glycoimmunologist Brian Cobb of Case Western Reserve University in Cleveland.

People with type A are also more prone to blood clots, Olsson says. When humans and their ancestors were having babies in caves and fighting predators without the option of an emergency room, such clotting may have been beneficial.
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Title Annotation:Genes & Cells
Author:Ehrenberg, Rachel
Publication:Science News
Geographic Code:1USA
Date:Dec 1, 2012
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