Still, proponents claim lists of hundreds clamoring for cloning services and 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, say animal cloners. 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. Monday, California scientists reported that two recently cloned cows died, presumably because immune-system defects left them unable to fight infection. Nor have scientists yet cloned primates, humans' closest relative. Surrogate mothers may experience risky miscarriages, stillbirths at the least a hard pregnancy, carrying both a fetus and placenta that are abnormally large. Some cloned animals were born twice as large as they should be.