Dolly the Sheep: First Cloned Adult Mammal Announced

Scientists at the Roslin Institute in Edinburgh, Scotland, announced on February 22, 1997, that they had successfully cloned an adult mammal for the first time. Dolly the sheep was born on July 5, 1996, created from a single cell taken from the mammary gland of a six-year-old Finn Dorset ewe. Lead researcher Ian Wilmut and his team had made 277 attempts before one produced a viable embryo. The breakthrough overturned the prevailing biological assumption that adult mammalian cells were irreversibly specialized and could not be reprogrammed to create an entire organism. Dolly lived for six years and gave birth to several lambs naturally before developing lung disease and arthritis. Her early death raised questions about whether cloned animals age prematurely, since her DNA came from an older donor. The announcement triggered immediate global debate about the possibility and ethics of human cloning, leading twenty countries to ban reproductive human cloning within a decade.