by nomo » Mon Jul 31, 2006 5:38 pm
Raising Beast People<br>Science is blurring the line between humans and animals.<br>By Lee M. Silver<br>Newsweek International<br><br>July 31, 2006 issue - High up on the bluffs overlooking the Pacific Ocean in southern California, strange animals scurry about in their cages. They eat, drink, copulate and occasionally try to run away from human hands that enter their confined quarters. If you didn't know better, you would think they were ordinary mice. But these particular animals contain a hidden component not present in their naturally conceived cousins. Inside their brains are living human neurons that help them to see, hear and think.<br><br>Fred Gage, a biologist at the Salk Institute, has created these part-human animals to understand how human neurons degrade or die in people suffering from neurodegenerative diseases such as Parkinson's and Alzheimer's. Studying and perturbing brain cells in their natural environment—which is to say, inside a functioning brain—provide the best hope for developing therapies to prevent or overcome disease symptoms. But experimentation on human brains is obviously unacceptable, and so scientists are hoping that animals with a small percentage of human brain cells will provide a substitute for human subjects.<br><br>Many people, however, are deeply disturbed by this research. U.S. President George W. Bush believes that scientists like Gage have stepped across a moral line that must be defended, even at the cost of biomedical progress. In his 2006 State of the Union address, he implored Congress to "pass legislation to prohibit the most egregious abuses of medical research [including] creating human-animal hybrids," because "human life is a gift from our Creator" that should never be "devalued." Bush has already set back progress on research on stem cells, which are harvested from days-old embryos, by putting restrictions on their use. Now he and other leaders may be girding to attack the next promising area of biological research.<br><br>Scientists call these part-human animals chimeras, after the creature in Greek mythology with the head of a lion, the torso of a goat and a tail sprouting the head of a venomous snake. The Greeks considered the chimera a monster because it violated a perceived "natural order" in which each species is a separate and unique category. So profound was this violation thought to be that thinkers over the millenniums have assumed such creatures could not possibly exist in reality. This conventional wisdom was shattered in March 1984, when an animal unlike any other ever born, or seen, adorned the cover of Nature, the international journal of science. Danish embryologist Steen Willadsen had mixed cells from the embryos of a sheep and a goat in a petri dish and created a "geep"—a mosaic animal with the head of a goat and the woolly upper torso of a sheep. The geep wasn't much more than a biological curiosity. In the past few years, however, explosive advances in stem-cell biology have provided scientists with the ability to create human-animal chimeras—a development that could potentially revolutionize biomedical analysis and therapy.<br><br>This progress raises a simple question: how far should scientists be allowed to go down the chimera path? Unfortunately, there is no simple answer. On one side are the potential benefits to biomedical research and human health. On the other, there's our deep-seated abhorrence to the idea of combining humans and animals—and the weird possibility that the animals we create for purposes of experimentation could wind up falling under our definition of persons, with all the rights that follow.<br><br>Efforts to create human replacement organs are probably the least controversial use of chimeras. By implanting human stem-cells—which have the potential to become any type of adult tissue—into animal fetuses or embryos, biomedical scientists hope to produce animals that develop a human organ, such as a liver or kidney, in place of the animal version. Progress along these lines has already been made. In 2002, Alan Flake at Children's Hospital in Philadelphia and Esmail Zanjani at the University of Nevada incorporated human stem cells into early sheep fetuses while they were growing in their mothers' wombs. After birth, a wide variety of lamb tissues including blood, cartilage, muscle and heart displayed human contributions of up to 40 percent, though external body features were always entirely animal-like. In 2003, Yair Reisner at the Weizmann Institute in Israel implanted nondescript human kidney stem cells into mice, and coaxed the cells to multiply and develop into miniature, but fully functional, human kidneys that actually secreted urine. Results obtained from these lines of research and others suggest that the creation of chimeras may be key to coaxing human stem cells to develop into fully functional replacement kidneys, livers and hearts.<br><br>The prospect of pigs with human hearts may cause people to shudder at first, but societies that accept other lifesaving biomedical technologies will likely come around on this one as well. While objections will certainly be voiced by a few, including animal-rights activists and other opponents of biotechnology, I suspect their numbers will be too small to make a difference. The debate line shifts, however, when scientists begin to "chimerize" the essential features of mentality that distinguish us as human beings. Because education leads to an understanding that human mentality emerges from human brains, the notion of chimeric mice with human brain cells is likely to disturb many more people.<br><br>Last December, Gage injected human embryonic stem cells into the brain regions of developing mouse fetuses still inside their mother's uteruses. The human cells became "active human neurons that successfully integrate into the adult mouse forebrain," where higher brain function is localized, Gage explained. Although Gage's mice still have brains that are less than 1 percent human, Stanford professor Irving Weissman believes that mice with brains made entirely of human cells would make a better "model" for human neurological diseases, and he's proposed creating them. Would a mouse with a 100 percent human brain cross a moral red line?<br><br>No biologist thinks a mouse-size brain filled with human cells could produce anything remotely resembling human consciousness. But the presence of a biologically human brain inside an organism able to propel and feed itself is typically accepted as clear biological evidence that the organism is a human being. This logic would force an ethical person to grant the chimeric mouse I've just described a right to life, which is patently absurd. Yet if we follow our intuition and decide that this mouse is not a human being, we are forced to conclude that the presence of a fully human brain inside an alert, responsive organism is not a sufficient criterion for inclusion within the family of human beings, which not only violates common sense but challenges the very foundation of universal human rights.<br><br>The moral conundrums provoked by animal-human chimeras multiply tremendously when the companion species is not a mouse but a nonhuman primate with a far larger brain capacity. So far, scientists have integrated only small numbers of human neurons into monkey brains. Although members of the scientific community have no intention of creating chimeras with even minimal human-specific mental attributes, the fact is that modern biotechnology has moved such ambiguous beings from the realm of mythology to that of possibility. And this fact elicits the greatest challenge to Western thought, which is that the existence of a strict line separating human beings from nonhuman beings may simply be a figment of our imagination.<br><br>Silver is a professor at Princeton's Department of Molecular Biology and the Woodrow Wilson School of Public and International Affairs. He is also the author of "Challenging Nature: The Clash of Science and Spirituality at the New Frontiers of Life." He has no financial interests in or consulting arrangements with any biotechnology or pharmaceutical company.<br>© 2006 Newsweek, Inc.<br><br>URL: <!--EZCODE AUTOLINK START--><a href="http://www.msnbc.msn.com/id/13989043/site/newsweek/">www.msnbc.msn.com/id/1398.../newsweek/</a><!--EZCODE AUTOLINK END--> <p></p><i></i>
