The Unintended Consequences of Animal Gene Editing

The purported birth last month of the world’s first gene-edited human babies, claimed by a Chinese scientist, spurred a wave of global outrage. Scientists denounced the (as yet unconfirmed) experiment as irresponsible, and the development reinforced fears that the redesigning of DNA is moving ahead too fast and without necessary oversight.

The proliferation of similar experiments on farm animals in recent years supports those concerns. Though rapid strides have been made to map genomes—the full set of genes for humans, animals, insects and plants—scientists have only begun to understand what the tens of thousands of individual genes do. Moreover, they are far from unraveling how those genes interact with each other.

Scientists around the world are editing the genes of livestock to create meatier pigs, cashmere goats with longer hair and cold-weather cows that can thrive in the tropics. The goals are to improve agricultural productivity, produce hardier beasts and reduce practices that are costly or considered inhumane. But amid some successes, disturbing outcomes are surfacing.

When Chinese researchers deleted a gene that limits muscle growth in mammals so that rabbits would grow leaner, their creations exhibited an unusual characteristic: enlarged tongues. Similar experiments on Chinese pigs led some to develop an additional vertebrae. Gene-edited calves died prematurely in Brazil and New Zealand.

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