Some believe the greatest emerging threat to the human race can be found in the Middle East, where terrorists seek weapons of mass destruction. Others point to melting glaciers, adamant they have discovered proof of environmental doom.

I suspect a far greater threat to our species emerged this month in a politely worded report issued by a British parliamentary committee.

Last December, the British government published a white paper ostensibly calling for a ban on creating what it called "inter-species embryos." The suggested prohibition, however, was not absolute. It would have left Parliament the power to approve exceptions for research purposes.

Britain then began considering a new law that would allow government-licensed researchers to create embryos that were part human and part animal.

As British parliamentarians saw it, the big question was not whether scientists should be allowed to create human-animal hybrids, but exactly what types of hybrids should be permitted and what rules should govern their willful creation and destruction.

A panel of lords, baronesses and members of the House of Commons pondered the issue for two months. On Aug. 1, it published a modest proposal that could have been drafted by Jonathan Swift.

First, the committee tried to precisely define an "inter-species embryo." It initially settled on four types: a "true hybrid," created by uniting an animal egg with a human sperm or vice versa; a "cybrid," created by placing the nucleus of a human cell in an animal egg; a "transgenic embryo," created by introducing human DNA into an animal embryo; and a "chimera," created by implanting animal cells into a human embryo.

Having defined these four creatures, whose actual construction is apparently within the reach of contemporary technology, the committee turned its attention to the undeniable reality that once the door of the human-hybrid laboratory is unlocked, researchers venturing there may come up with new -- perhaps unimaginable -- permutations of man and beast.

The government white paper, it turns out, had pre-emptively suggested a "catch-all" provision, covering any embryo at least 50 percent human. This was in keeping with the government's position that scientists (at least for now) should not be granted licenses to create "true hybrids" -- which the government deems to be 50 percent human.

The parliamentary committee rejected this cutoff point, arguing there was no logical reason to it.

No sooner had the committee begun debating just how many percentage points of humanity an embryo must possess before it ought to be considered human than a thorny question of bureaucratic jurisdiction arose. Continued...