Sen. Sam Brownback (R-Kan.) and Sen. Mary Landrieu (D-La.) introduced the Human-Animal Hybrid Prohibition Act of 2009 earlier this week. The Act defines human-animal hybrids as:

(A) a human embryo into which a non-human cell or cells (or the component parts thereof) have been introduced to render the embryo's membership in the species Homo sapiens uncertain;

(B) a hybrid human/animal embryo produced by fertilizing a human egg with non-human sperm;

(C) a hybrid human/animal embryo produced by fertilizing a non-human egg with human sperm;

(D) an embryo produced by introducing a non-human nucleus into a human egg;

(E) an embryo produced by introducing a human nucleus into a non-human egg;

(F) an embryo containing at least haploid sets of chromosomes from both a human and a non-human life form;

(G) a non-human life form engineered such that human gametes develop within the body of a non-human life form; or

(H) a non-human life form engineered such that it contains a human brain or a brain derived wholly or predominantly from human neural tissues.

Engaging in such research could result in ten years in prison, a million dollar fine, or both. Let's see what research this act would ban. 

Provision (A) might prohibit research that aims at the creation of human organs in other animals suitable for transplant in human patients such as the work already done by Esmail Zanjani at the University of Nevada Reno. 

If the goal of provisions (B) and (C) is to prevent the creation of bovine/humans or canine/humans by interspecies mixing of sperm and eggs, they are superfluous since fertilization between species that widely separated by evolution is highly unlikely. On the other hand, perhaps the senators are worried about the creation of humanzees. Experiments from more than 30 years ago have shown that human sperm can penetrate gibbon eggs. In addition, the only known experiments in which a Russian biologist tried to fertilize chimpanzees using human sperm failed. Finally, would these provisions outlaw a fairly common IVF assay in which human sperm are tested for fertility using hamster eggs?

Provisions (D) and (E) would outlaw experiments in which researchers have already tried to produce stem cell lines using enucleated animal eggs into which human cell nuclei have been installed. The idea is that animal eggs, which are far more plentiful and easy to get than are human eggs, could be used to produce stem cell lines that were 99 percent human. Unfortunately, recent research has strongly suggested that this way of producing therapeutic stem cell lines will not work since animal eggs have failed to reprogram the human DNA into stem cells. So far as I can tell, given their scarcity, no one has tried to install animal nuclei into enucleated human eggs. Of course, this might change if it turns out that stem cells can be converted into eggs and sperm

Provision (F) is very much like Provisions (B) and (C) since the most likely to way to combine human haploid cells with animal haploid cells to produce a diploid embryo would be to combine animal and human eggs and sperm. Perhaps this provision would also outlaw the addition of any single human chromosome to an animal embryo and vice versa. 

Provision (G) would outlaw a technique in which human stem cells might be injected into an early animal embryo (say, a mouse) and some of those cells might differentiate into human sperm producing or egg producing cells in mice. Human gametes might then be harvested from the mice and combined using IVF techniques to produce a completely human baby. This far out technique could be used to produce viable sperm and eggs for people who are otherwise infertile. Of course, the safety of such a procedure needs to be rigorously verified, but it is not clear why it would be, ipso facto, ethically suspect. 

And Provision (H) would apparently ban experiments like the ones in which human embryonic stem cells are injected into the brains of embryonic mice where they develop into functioning human neurons. The idea is not to produce Stuart Littles but develop animal models to study human brain diseases. Doing a similar experiment with chimpazees gets closer to an ethical line since it is more likely that installing human brain cells in a chimp might confer some human characteristics, say language ability, on such a chimp/human chimera. So if that's what Brownback and Landrieu are really worried about they should advocate banning primate/human brain chimeras and leave the other research alone. 

Preventing the advent of human-animal hybrids and chimeras is an ongoing obsession of Sen. Brownback. He introduced similar legislation back in 2006. The senator from the Sunflower State explains why he introduced the bill:

"This legislation works to ensure that our society recognizes the dignity and sacredness of human life," said Brownback. "Creating human-animal hybrids, which permanently alter the genetic makeup of an organism, will challenge the very definition of what it means to be human and is a violation of human dignity and a grave injustice."

Nonsense. As the above review shows, current research which combines animal cells and genes with human cells and genes is not "a violation of human dignity and a grave injustice." Outlawing such research would be just such a violation and injustice.