Core Viewpoint - The research conducted by Yoshinori Nakagawa and his team demonstrates that continuous cloning in mammals is not sustainable due to the accumulation of genetic mutations over generations, ultimately leading to the termination of the cloned lineage [4][3]. Group 1: Cloning Experiment Overview - The cloning experiment initiated in 2005 involved using somatic cells from a female mouse to create successive generations of cloned mice through nuclear transfer, resulting in a total of 58 generations and over 30,000 cloning attempts [9][7]. - Initially, the cloning success rate improved, reaching 15.5% by the 26th generation, but began to decline significantly after the 27th generation, dropping to 0.6% by the 57th generation, with all 58th generation clones dying shortly after birth [7][9]. Group 2: Genetic Mutations and Their Impact - Despite appearing normal in weight and lifespan, the cloned mice accumulated harmful genetic mutations, with an average of 69 single nucleotide mutations and 1.4 small insertions/deletions per generation from the 1st to the 57th generation [11][10]. - Large chromosomal structural variations, such as complete loss of an X chromosome and significant deletions or translocations, were also observed, particularly during the decline in cloning success rates [11][10]. Group 3: Sexual Reproduction as a Solution - The study found that the cloned mice could successfully reproduce through sexual reproduction, although the number of offspring was significantly reduced to an average of 2-3 compared to the normal 10 [13][12]. - Subsequent generations born from these sexual reproductions showed a recovery in offspring numbers and normal placental sizes, indicating that sexual reproduction acts as a "proofreading system" to eliminate accumulated genetic errors [13][12]. Group 4: Implications for Cloning Technology - The research highlights the evolutionary necessity of sexual reproduction in mammals, which helps eliminate harmful mutations and maintain genetic diversity, contrasting with the limitations of cloning [15][16]. - The findings suggest that while cloning can serve as an emergency measure for preserving genetic material, it cannot replace natural reproduction for sustaining healthy populations, especially in conservation efforts for endangered species [16][15].