A Man or a Mouse? Or Both?
What happens when you cross a human and a mouse? Sounds like the beginning of a bad joke but, in fact, it's a serious experiment recently carried out by a research team headed by a distinguished molecular biologist, Irving Weissman, at Stanford University. Scientists injected human brain cells into mouse fetuses, creating a strain of mice that was approximately 1% human. Weissman is considering a follow-up experiment that would produce mice whose brains are made up of 100% human cells.
What if the mice escaped the laboratory and began to proliferate in the outside environment? What might be the ecological consequences of mice with human brain cells let loose in nature?
Weissman says that, of course, he would keep a tight rein on the mice and if they showed even the slightest signs of humanness, he would kill them. Hardly reassuring.
In a world where the bizarre has become all too commonplace, few things shock the human psyche. But experiments like the one that produced a partially humanized mouse stretch the limits of human tinkering with nature to the realm of the pathological.
This new research field -- creating hybrid creatures out of different species -- is at the cutting edge of the biotech revolution and is called chimeric experimentation (after the monster of Greek mythology that was part lion, part goat and part serpent).
The first such chimeric experiment occurred many years ago when scientists in Edinburgh, Scotland, fused together a sheep and goat embryo -- two completely unrelated animal species that are incapable of mating and producing a hybrid offspring in nature. The resulting creature, called a geep, was born with the head of a goat and the body of a sheep.
Now, scientists have their sights trained on breaking the final taboo in the natural world -- crossing humans and animals to create new human-animal hybrids of every kind and description. Already, aside from the humanized mouse, scientists have created pigs with human blood running through their veins and sheep with livers and hearts that are mostly human.
The experiments are designed to advance medical research. Indeed, a growing number of genetic engineers argue that human-animal hybrids will usher in a golden era of medicine. Researchers say the more humanized they can make research animals, the better able they will be to model the progression of human diseases, test new drugs and harvest tissues and organs for transplantation into human bodies.
