According to a long-running study published in Nature Communications, scientists in Japan have found that you can’t just keep cloning clones of living things indefinitely and expect things to turn out okay in the end. Eventually, the chain of clones starts to collapse.
For nearly 20 years, a research team led by Teruhiko Wakayama at the University of Yamanashi has been serially cloning mice, meaning cloning a mouse, then cloning its clone, and then cloning that clone, and onward for generations. Early results suggested that the chain could go on indefinitely, as the process kept producing healthy mice well into its 20th generation.
And then things went awry.
By the time the researchers passed the 25th generation, success rates began to decline. By generation 58, the cloned mice didn’t survive beyond birth. Genome sequencing revealed what was going wrong: mutations stacking up over time, especially large structural changes to DNA that don’t get “cleaned up” in cloning the way they do in sexual reproduction.
Each new clone carried a few more genetic errors than the last. Some small ones, but also bigger structural glitches. At first, natural selection within the lab process helped filter out the worst cases. But over time, the buildup overwhelmed whatever advantages the system had.
Weirdly, the cloned mice themselves weren’t always the problem. A lot of them lived normal lifespans, even with severe genetic damage just beneath the surface. The real problem showed up in fertility rates and developmental issues. Some were born with abnormal placentas. When later-generation clones reproduced the old-fashioned way, their offspring were often healthier, more stable, and genetically closer to the baseline.
It’s some complex science that’s been dumbed down here for legibility, but the main takeaways here are that sexual reproduction has several important functions in the creation of healthy life that the cloning process can’t replicate just yet, if ever. Natural sexual reproduction performs a kind of genetic maintenance that reshuffles DNA, filters out damage, and overall keeps organisms from falling apart over time.
For all of its sci-fi promise, cloning, whether it be for agricultural or biotech, may have a ceiling. Not a severely limiting one, but a ceiling nonetheless, because for now, there’s only so many times something can be copied before it degrades.
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