History of animal testing
In 1996 Dolly the sheep was born, the first mammal to be cloned from an adult cell. The process by which Dolly the sheep was cloned utilized a process known as nuclear transfer applied by lead scientist Ian Wilmut. Although other scientists were not immediately able to replicate the experiment, Wilmut argued that the experiment was indeed repeatable, given a timeframe of over a year.
Cloning
There were early claims that Dolly the sheep had pathologies resembling accelerated aging. Scientists speculated that Dolly's death in 2003 was related to the shortening of telomeres, DNA-protein complexes that protect the end of linear chromosomes. However, other researchers, including Ian Wilmut who led the team that successfully cloned Dolly, argue that Dolly's early death due to respiratory infection was unrelated to deficiencies with the cloning process. This idea that the nuclei have not irreversibly aged was shown in 2013 to be true for mice.