"a metaphysical difference between humans and nonhuman animals"

….For researchers, however, “there’s nothing sacramental about the boundaries between the species,” and interbreeding, therefore, “is just moving around cellular or genetic materials in the world,” says Arizona State University bioethicist Jason Robert. Esmail Zanjani, an animal biotechnologist at the University of Nevada School of Medicine, has grown sheep with human livers; Irving Weissman, director of the Institute for Stem Cell Biology and Regenerative Medicine at Stanford University, has created mice with human brain cells; and many researchers are taking the first steps toward stem cell therapy by injecting human cells into mice, monkeys, and other animals. Evan Snyder of the Burnham Institute in La Jolla, California, argues that these sorts of experiments allow scientists to work out the kinks in such therapies on a monkey or rat rather than “your child or grandmother.”

Like Snyder, most biologists working to combine species aim to help humans or to advance scientific knowledge, not to selfishly cook up a Frankensteinian manimal. Zanjani, for instance, hopes human organs grown in animals could help shorten transplant waiting lists. Still, the intermingling makes many uneasy. Robert and other bioethicists have identified some potential underlying reasons for these fears: In essence, man-animal chimeras and hybrids could lead to a type of moral confusion, leaving us unsure of how we are supposed to treat the resulting creatures and whether we should be performing medical research on them at all. Regardless of their religious beliefs or lack thereof, most people do find something “special” about the human species, Robert says. “For people of faith, it’s going to be a metaphysical difference between humans and nonhuman animals. For others, it’s going to be something else, such as culture or self-consciousness, that explains the differences between human and nonhuman animals.”

This sense of specialness also underlies many of the negative responses the researchers at the Broad Institute received. “The reason there is all this discussion is because a lot of people still today simply can’t wrap their minds around the idea that we’re animals,” says Pigliucci, who has a particular interest in the way we think about evolutionary theory. “We may be special animals, we may be particular animals with very special characteristics, but we’re animals nonetheless; we have cousins and relatives all over the animal world, and, therefore, by implication of course, we were not created from nothing by an intelligent designer. That really hurts a lot of people.”

Sara Via, an evolutionary biologist at the University of Maryland, echoed this sentiment in a recent AAAS talk on speciation: “Many people don’t want to accept that humans aren’t on the top of the heap evolutionarily and certainly not that humans may have evolved from something that resembles a lowly monkey.”

Scientists are not immune to illusions of distinct separation, says Pigliucci. “I am certainly not going to claim that at a subconscious level, there’s been no bias amongst scientists themselves in terms of human biology,” he says. “I’m sure that it is difficult to look not only at humans, but at our closest relatives, in a completely detached way. I know several primatologists, and I don’t know any of them who doesn’t feel more than just a scientific curiosity toward their subject of investigation. They clearly understand and they feel that they’re dealing with very special animals because they’re so closely related to us.” But new information, such as the complete sequence of human and some animal genomes, is allowing scientists to factually confirm, again and again, our similarities to other species. We share with chimpanzees more DNA than previously thought; other primates, known as bonobos, have constructed societies in which they display moral rules; and elephants and other long-living species are now believed to suffer from psychiatric conditions like post-traumatic stress disorder. The ability to uncover these commonalities—and to be surprised by them—highlights the true benefit of the scientific worldview, Pigliucci says: its flexibility.

“Your regular person on the street thinks of a scientist as someone who’s certain. Scientists know facts. They’re objective. But that’s not science at all,” says Via. “Science is a view of life in which new information is admitted, not denied, and we use that information to always make that view better.” ….

…from:

Of Manimals and Humanzees
The idea that humans and chimps interbred causes discomfort in some circles, even as science explores the potential benefits of hybrids and the blurring of what was once a bright line between species.
by Cindy Kuzma