Chimeras: Breaching the species boundary
D. Balasubramanian
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Making a hybrid between man and chimpanzee is technically possible
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HAYAGREEVA, OR the horse-headed human, was the form Lord Vishnu took in order to save Brahma from two Asuras.
Vishnu comes again as part lion, part human in the Narasimhavatara in order to kill the arrogant king Hiranyakashyapa. Hindu scriptures and mythology have several such examples of chimeras. A charming one is that of Lord Ganesha who has the elephant head and human body.
Origin of the name
The very name chimera is from Greek mythology; Homer writes of the daughter of the giant King Typhon and Queen (half serpent) Echidna, called chimera (literally meaning a young she goat). She is part lion, part she goat and the rest a serpent. The hero Bellerophon, who comes on the winged horse Pegasus, vanquishes her.
Chimeras mix species in an individual. Biology, as we knew it, did not allow the mixing of species. The great biologist Ernst Mayr, who passed away recently at the ripe age of 100, defined a species as one that breeds only within its own members, and does not interbreed with another.
Artificially interbred ones such as the mule are sterile, genetic dead ends. A chimera is thus an individual of one animal species with its own cells and that of another animal species growing side by side within its body. Since species cannot interbreed, chimeras do not belong to the natural world. Modern biology has broken this barrier. Not long ago, biologists at the University of California at Davis fused together the embryos of two distinct species, a goat and a sheep.
In the offspring, called by the ridiculous sounding name `geep', every organ, including the sex organs, were made up of both goat and sheep cells.
This meant that the geep could produce both goat and sheep. The species boundary was breached, and that started raising ethical issues. If this could be done with farm mammals, what happens when someone starts doing the same with humans?
Mouse chimeras are already being used in laboratories. Last year, Charlotte Kuperwasser at Tufts University created a mouse into which human breast tissue was grafted.
Great experimental tool
Using this, she studies normal breast development and creates human breast cancers in mice. She sees this as an excellent experimental tool for drug testing and a means towards the cure for breast cancer.
Dr. Irving Weissman at Stanford created a mouse with human neurons in its brain, with the ultimate aim of understanding and treating Alzheimer's and Parkinson's diseases.
Each of them has strictly adhered to the guidelines imposed on them by their institutional ethics committee. Yet there are worries in many minds that some scientists might inadvertently (or otherwise) open an unwelcome Pandora's box.
Organ transplantation is now a standard surgical procedure. Donor human organs are in short supply. It does appear possible to use animal organs in some instances. Transplantation across species, wherever possible, will clearly come about wherever human need takes precedence.
Raising ethical questions
But it does raise ethical and even philosophical questions, as summarised by Ms. Carolyn Johnson in her recent report in The Boston Globe.
She points to the case of the chimera called the `humanzee' (another awkward name). Dr Stuart Newman of the New York Medical College had proposed making the hybrid between man and chimpanzee, two closely related species.
This is technically possible today. Just as the geep, it raises ethical and even moral questions. The U.S. Patent Office rejected the patent claim on this human-chimp mix on the basis of slavery — you cannot own a being with human genetic material. The U.S. Council on Bioethics is still struggling to draw the border between the usefulness of such a human-animal hybrid and `high tech bestiality.'
With the advent of stem cell technology, such chimeras will become more and more doable and commonplace. Ethical guidelines and even national (and international) laws will have to be drawn up at the soonest.
The U.S. National Academy of Sciences has recently come out with guidelines on the use of human embryonic stem cells, and stipulates that no animal into which human embryonic stem cells have been introduced at any stage of development should be allowed to breed.
Drawing guidelines and rules, and following them across the world is not going to be easy. There are many belief systems around the world. Some read the Bible as giving humans supremacy over animals.
The U.S.-based Christian Medical Association points out that while putting an animal kidney into a human is all right, we cannot abuse an animal for our good. They also state it to be immoral to create a human whose status cannot be clear. Other religions would agree with this and some might even go further and even object to transplanting animal parts into people.
It is with these in view that global bodies such as international scientific unions and the UNESCO are getting together and drawing up guidelines that member nations and scientists will have to follow. One such meeting at the UNESCO is scheduled in early July. It does not come a day too early.
dbala@lvpei.org
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