Dolly the sheep was born on July 5, 1996, at the Roslin Institute in Scotland, the only surviving lamb from 277 attempts. Frogs had been cloned in 1958, but scientists believed a specialized adult cell was locked for good. The Roslin team, funded by PPL Therapeutics and the Ministry of Agriculture, used somatic cell nuclear transfer: an emptied egg from one ewe, the nucleus of a mammary gland cell from another, a small electric shock to restart development, and a surrogate to carry the pregnancy. Because the donor cell came from a mammary gland, she was named after Dolly Parton, and her existence was kept secret until February 22, 1997.

Dolly never left the Roslin Institute, slept indoors every night for security, and bred normally, producing six lambs. She developed arthritis at four and was euthanized on February 14, 2003, at age six with a lung cancer caused by the retrovirus JSRV. Her short telomeres fed a born-old narrative, but a 2016 study of 13 cloned sheep found they aged normally. The episode follows her legacy into pet cloning, conservation and stem cell science.

• Bonnie in 1998, twins Sally and Rosie, and triplets Lucy, Darcy and Cotton in 2000
• Why the indoor barn, not cloning, likely explains the lung disease that killed her
• Commercial cloning prices of about 50,000 dollars for a dog, 30,000 for a cat and 85,000 for a horse
• The Pyrenean ibex cloned in Spain in 2009, which died shortly after birth from lung defects
• The first cloned macaques in China in 2017 and five gene-edited clones in 2019, leading to induced pluripotent stem cells