But extracting the cells requires destroying the embryos, which are typically left over from in vitro fertilization attempts.

Removal of the cast requires destroying the cast itself.

Restoring market confidence will require destroying a substantial portion of the country's 11 million cattle.

But to wipe out the Forum and the Senate would require destroying the imperial palace, and that's far more difficult.

But the idea has raised ethical concerns because it would require destroying a cloned embryo to extract its stem cells.

"But harvesting it requires destroying an entire acre of forest just to find two or three ipe trees."

There appears to be an older structure beneath the site but trying to reach it would require destroying the ruins.

While acknowledging the promise of the research, others have moral objections because obtaining the cells requires destroying human embryos.

"But that would require destroying a fairly large section of cloth," Bishop Caines protested.

"The core ethical problem is that this research requires destroying human beings at the embryonic stage," he said.