And they told Congress last week that they could perform it safely simply by testing clone-embryos for defects before implanting them into women. But if such tests were available today, animal cloning wouldn't fail so often, animal cloners say. Despite headlines and photographs of Dolly the sheep and cloned cows, pigs, goats, and mice, most animal clones still die, usually during embryonic development. Others are stillborn with monstrous abnormalities. Bloated mothers have laborious miscarriages, and occasionally die themselves.
Clones struggle for air in intensive care, only to have to be euthanized.
Even initial survivors remain fragile. On Monday, California scientists reported that two recently cloned cows died, presumably because immune-system defects left them unable to fight infection. And scientists haven't yet cloned primates, humans' closest relative. Some cloned animals were born twice as large as they should be. Some babies who survive birth will die in days or weeks from abnormal hearts, kidneys, livers, or lungs.