Is a human-chimpanzee hybrid morally repugnant?

On doctor's orders, I didn't watch, but I understand that one of the bold new initiatives put forth last night was something like, "Tonight I ask you to pass legislation to prohibit the most egregious abuses of medical research – human cloning in all its forms … creating or implanting embryos for experiments … creating human-animal hybrids …"

Technically speaking, as far as we know, a human-animal "hybrid" per se is not possible. Hybridization requires that two species be mutually fertile. For example a mule is a (sterile) hybrid of an ass and a mare. Lions and tigers, believe it or not, can interbreed, as can anise and dill. But the Great Moralist was talking about other possibilities, even if he didn't understand what he was saying.

Cloning, as such, really comes into this only in a very limited way. The method which has been used to clone sheep and other mammals is called Somatic Cell Nuclear Transplant, in which the nucleus from a cell of one animal -- just about any old cell, such as a skin cell -- is placed into an ovum from which the nucleus has been removed. This chimeric cell may then start to behave like a normally fertilized ovum, and develop into an embryo. The nucleus contains more than 99% of a cell's genetic material, including all of the genes which guide development, hence the new creature will be nearly identical to the one from which the nucleus was taken. However, the cells of people and all multicellular organisms, called eukaryotic cells, contain endosymbionts -- the descendants of ancient bacteria, called mitochondria, which are essential to cellular metabolism, and have their own DNA. Hence if you were to put a human nucleus into, say, a denucleated cow ovum, and get it to develop, you would get a human being in every respect, except for its mitochondrial DNA. You wouldn't be able to tell that there was anything unusual about the person unless you were to sequence its mitochondrial DNA (assuming that there wasn't some metabolic disorder associated with the situation, which is unknown).

There are other ways of combining human and animal genes in one being. One which is being actively pursued is xenotransplantation. If organs from, say, pigs, could be modified so that they did not provoke an immune response from humans, they would be available for transplant. That has actually been tried, by doctors who unsuccessfully transplanted a baboon's heart into a baby. This was widely considered unethical, but only because the experiment had little chance of success and only added to the baby's suffering. No doubt if it had worked it would be done all the time now, and people would view it as a method of saving lives, not a moral abomination.

Another kind of experiment, which has been done, is to grow specific human tissues within animals. For example, human cancer cells can be made to grow in mice, to test theories about cancer or to test treatments. Yet another procedure, which is now done routinely, puts single genes that code for a specific protein into a foreign species. For example, genes for human hormones have been introduced into goats, so that the hormone can be extracted from the goats' milk for medicinal purposes.

A morally more questionable procedure is to add one or more embryonic stem cells from species A to an embryo of species B. If such an embryo is viable, what will probably happen is that it will follow the developmental pathway it has already established, in other words develop into animal A, but the adult animal will have cells of the other species interspersed throughout its tissues. Who knows what, if any, gross abnormalities might be associated with this situation?

Then there is the science fiction scenario, well outside the present capabilities of science, of using genetic engineering techniques to equip humans with attributes of other species, such as wings or gills.

Note that only the first of these techniques necessarily involves cloning, and that some of them appear to be morally troubling but others do not. The American Journal of Bioethics did a major consideration of "crossing species boundaries" in 2003, with a lead essay by Jason Scott Robert and Francoise Baylis. There are nearly two dozen responses, which may be a bit much, but I recommend reading at least a couple to get a flavor of how these issues are debated.

Robert and Baylis point out that defining the boundaries among species is quite uncertain. While humans are biologically distinguishable, it is not at all settled what characteristics give an entity the moral status of a person. Most ethical arguments against creating any sort of part human creature are not very convincing, but they find the most convincing one is simply the confusion it would cause. Presently we have an unexamined, "folk" consensus that humans are morally distinct entities, and it just seems dangerous to start muddying the waters too much.

Frankly, I don't see the waters muddied by, say, a person with a transplanted pig's liver, or a laboratory animal that includes some human cells or tissues for purposes of medical research. (Animal rights advocates will be offended, but that is a separate issue and certainly not the concern behind the SOTU admonition.)

What do you think?