The Greek stories described Chimera as a mix between a lion, goat and dragon (mainly). A "creature" that could not be classified due to how many animal genes it was born with. However the Chimera's that are the focus of this article are human or at least contain human biology.
The first documented (natural) human chimera is a blood chimera. In 1953 Northern England, Mrs. McK donated blood to help those in need. Her blood was received and screened in a lab, checking Mrs. McK's blood to make sure she did not have any diseases. It was then that the local doctor found that she had two different blood types. He sent the blood to Specialists at London's Medical Research Council Blood Group, Doctors Robert Race and Ruth Sanger who confirmed that Mrs. McK did indeed carry two different blood types. The doctors were baffled of how such a thing could be possible. However, earlier a colleague of Doctors Race and Sanger's had published an article about fraternal twin cows that both carried two different blood types. Doctor Race then concluded that Mrs. McK was a twin and that during gestation her twins blood must have infused within her where it still cycled up to that date. Mrs. McK did later confirm that she had a twin brother who had died three years earlier.
It's common that most human chimera's at some time in history had a twin. A current theory on how they come about is that "...genetic chimeras develop spontaneously when fraternal twin embryos fuse or when one twin absorbs the other". Vanishing Twin Syndrome is the proper name of the absorption process.
In 1984 British geneticist created the Geep, an animal that was half goat and half sheep. It was a sterile animal that lived out it's life and then died. Scientists have infused human genes into rabbit embryo's to study stem cells and when the researches harvest the stem cells it destroyed the embryo's. Human genes were also infused sheep and pigs so that researches could harvest their organs and possibly use them for human transplants. Mice are infused with human brain cells to study neurologic diseases while mice infused with human immune systems are used for AIDS drug testing.
With this, the NIH are currently aiming to lift the temporary prohibition on animal human chimera research. While Human-Chimera testing is technically legal in the United States there are many who are opposed to it. Many have raised that because the "experiments" use human DNA it raises moral and ethical problems. What if an animal is fused with human DNA and lives on American soil, does that make the animal a pet or human? Are they then entitles to the same rights as humans? Questions like these are brought up all the time. While on the other side, scientists and researches stress that human-chimera research could help advance human medicine by seven days.





















