What do you get when you cross a sheep with a human? That sounds like a joke, but the question is no laughing matter; it's serious science. The result, a chimera, is an animal with cells from another animal. Recently, Esmail Zanjani, a scientist at the University of Nevada, announced he had created sheep with 15 percent human cells. His goal is to create partly human organs for people who need transplants.
The word chimera comes from a mythical Greek beast with a lion's head, a goat's body, and a snake's tail. Skeptics say that the prospect of growing human spare parts in sheep is still a distant dream. Modern cloning techniques, however, have allowed scientists to enter uncharted and, some people say, dangerous territory. Currently, no laws regulate the creation of chimeras--only voluntary guidelines from the National Academies. And the absence of legislation is, to some, as scary as the original Greek chimera.
In 2006, U.S. President George W. Bush called for "legislation to prohibit the most egregious abuses of medical research: human cloning in all its forms," including "creating human-animal hybrids." At the time, his speech left many people scratching their heads and wondering whether the president had just proposed a ban on mermaids. But Sen. Sam Brownback (R-Kan.) knew exactly what Bush meant.
"Human chimeras--long considered science fiction or mythology--have become reality," he said in a 2005 speech at Harvard Law School. "These hybrid creatures blur the line between humans and animals and [seriously] compromise human dignity."
Brownback proposed a law in 2006 banning human chimera research. One of his main concerns is that such research often uses human embryonic stem cells, the extraction of which destroys the embryo. Brownback is among many critics who consider that practice immoral.
Brownback also fears that mixing human and animal genetic material could create new diseases. Dr. Patrick Dixon, a lecturer on biological trends, worries that new viruses could be a "biological nightmare" for humans. "Mutant animal viruses are a real threat, as we have seen with HIV [the virus that causes AIDS]."
FACT VERSUS FICTION
Rather than creating new diseases, researchers argue, chimeras may help reveal the cures to existing illnesses. Irving Weissman, a leading chimera researcher at Stanford University in California, injects human brain cells into mouse fetuses to study brain diseases such as Alzheimer's and Parkinson's. Experimental drugs, which cannot be tested on humans, could be tested on chimeras to try to treat those diseases, he says.
Scientist Jonathan Moreno of the University of Pennsylvania helped set the National Academies guidelines on chimeras. He told Current Events he would welcome additional regulation but not an outright ban on "promising" research. "There's [too much] scaremongering," he says, adding that people imagine the human-animal hybrids from books such as H. G. Wells's The Island of Dr. Moreau.
"It's important to separate the science fiction from the facts," Moreno says. "Because science is hard, it's difficult to get a good public dialogue. We have this odd understanding about animal-human entities. I don't see that The Island of Dr. Moreau should be the basis of public policy."
HAS GENETIC ENGINEERING GONE TOO FAR?
Ask students: How should chimera research be regulated? By the scientific community? the government? both? What are the pros and cons of regulations that ban or severely limit new areas of research?
Notes Behind the News
More than 30 years ago, scientists fused a chicken egg with a quail egg to create a patchwork bird. One of the first mammal chimeras was a geep, a goat-sheep hybrid created in 1984 when scientists fused the embryos from both species.
Some newspapers have nicknamed Irving Weissman's chimera mice "Stuart Little mice," after E. g. White's clever fictional mouse. The tiny mice aren't likely to grow human brains, though. Mice brains are designed differently from human brains, and human stem cells develop in the mice as mouse cells. If mice brains begin to appear more human, Weissman says, he will stop his experiment.
Currently the National Academies guidelines prohibit breeding chimeras. The academies also prohibit the use of primates in human chimera research because the genetic closeness of the species raises concerns that human traits may emerge in other primates.
* Ask students to research and discuss current proposals to ban cloning. Find information on the science and ethics of cloning at learn.genetics.utah.edu/ units/cloning.
* Have students read fiction that features hybrid creatures. How might such stories influence public opinion about chimeras?
* Have students write stories featuring human-animal hybrids.
chimera (page 7)
A chimera (kigh-MIR-uh) occurs often in nature. (Every mother is a chimera, because she retains cells from her child.) Scientists create chimeras by fusing cells from one animal into another. To create a chimera that is part human, scientists extract stem cells, either from bone marrow or from a human embryo, and inject them into an animal embryo or fetus. Stem cells are used because they can become many different organs.