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Blood types were once thought to be with people for life. And, in almost every case, they're still thought to be with a person for life. But there is one patient whose blood type actually changed. A liver transplant, apparently, has a shot of changing a person's blood type.

There was once a simple time in human history when everyone had just one blood type, and that blood type was O negative. It wasn't called O at the time, of course, because even if anyone was looking at it, it would just have been blood to them.

But life kept up its usual trick of evolving, and suddenly, on the surface of the lovely, smooth, red blood cells were little agglutinations of protein. There was what's now known as the Rh factor, the thing that turns O negative blood into O positive blood.

Then there were other little clumps of protein, which separated Rh positive blood and Rh negative blood into A and B types. For the vast majority of history, only the Rh factor caused any bother.

The system of an Rh negative woman who became pregnant with an Rh positive baby could see the infant's blood type as an outside body, and attack it. This was such a selector that today eighty-five percent of people are Rh positive.

Meanwhile, A and B types only began troubling humankind by the time blood transfusions and organ transplants were happening. (Before that, any human blood or organs entering the body generally came via the stomach, which isn't that fussy about blood types.)

Again, the immune system would attack the strangely bedecked blood cells and cause medical problems. Type O patients, roughly forty-five percent of the population, could give out their blood and organs, but couldn't receive anyone else's. The Rh factor of the blood depended on what type of medical procedure was being done.

And so the world became concerned with these little blobs on blood, and with the genes that caused them. Since it was genetic, blood type was for life, and there was no way around the variations (Two more of which were found just recently.

The Junior and Langereis, which affect about 50,000 people in Japan.) so there wasn't anything to be done except finding universal O negative donors and draining them like Capri Sun juice bags. So imagine people's surprise when they found out that blood type can change.