A groundbreaking 20-year study conducted by researchers in Japan has revealed significant limitations in cloning technology, demonstrating that repeated cloning leads to an accumulation of fatal genetic mutations. The study involved cloning 1,206 mice from a single female donor between 2005 and 2025. Initially, the first 25 generations showed no apparent issues, but by the 58th generation, clones died shortly after birth due to accumulated genetic defects. This contradicts the long-held belief that clones are identical copies of their original donor. Developmental biologist Teruhiko Wakayama from the University of Yamanashi noted that mutations occurred at a rate three times higher than in naturally bred offspring. The research underscores the critical role of sexual reproduction in counteracting harmful genetic mutations, as the fertility of clones decreased over generations. The findings indicate that mammals cannot sustain their species through cloning alone. The researchers used nuclear transfer technology, similar to that used in the cloning of Dolly the sheep, but concluded that a new method is necessary to overcome the limitations of current cloning practices.