Remember this day when you pass a bio-engineered aardvark with a human face on your way to Yoga class in the not-too-distant-future. Today, some scientists launched a study to determine whether that aardvark should have a human penis as well.

The AP reports on the efforts of a group of British scientists to lay down some boundaries for the actually pretty established practice of splicing human DNA into animals' genetic code. (Earlier this year, for example, researchers added a human language gene to a mouse—and changed how it squeaked.) After controversy erupted last year in England over a plan to grow human embryos using cow and rabbit eggs, the scientists realized it might be a good idea to deal with these complex ethical issues BEFORE we inadvertently create a race of half-cow-half-man creatures who take over the Earth and, in a highly ironic but appropriate twist, begin humanely farming us.

It's the search for what bioethicists call the "yuck factor" (really!)—that point at which any reasonable person's stomach turns due to some deep-seated repugnance. And, though it dealt with a slightly different technology, I'm reminded of this awesome NYT Magazine piece from 2005, which showed just how bizarre the human-animal mixing game could get. In this passage, the writer James Shreeve describes an experiment wherein a scientist implants human stem cells into mice embryos:

If the experiment really works, the human cells should differentiate into all of the embryo's cell lineages, including the one that eventually forms the animal's reproductive cells. If the mouse were male, some of its sperm might thus be human, and if it were female, some of its eggs might be human eggs. If two such creatures were to mate, there would be a chance that a human embryo could be conceived and begin to grow in a mouse uterus — a sort of Stuart Little scenario, but in reverse and not so cute.

''Literally nobody wants to see an experiment where two mice that have eggs and sperm of human origin have the opportunity to mate and produce human offspring,'' says Dr. Norman Fost, professor of pediatrics and director of the bioethics program at the University of Wisconsin and a member of the National Academy of Sciences committee reviewing stem-cell research policies. ''That's beyond anybody's wildest nightmare.''

Yuck.