The Discovery of Mammalian Cloning: The Impactful Scientific Revelation Confirming its Perils
For decades, cloning has been synonymous with promise, mystery, and fascination. From the famous sheep Dolly (the first cloned mammal in 1996, over 30 years ago) to the most advanced experiences in modern biotechnology, the dream of replicating life seemed irresistible. However, after twenty years of unprecedented experience, science reminds us of an essential truth: nature imposes limits that cannot be ignored.
A study led by Japanese researcher Teruhiko Wakayama (Yamanashi University), recently published in Nature Communications, starkly demonstrates that cloning in mammals cannot be sustained indefinitely. At a certain point, the clones simply stop being born. This is not due to chance or poor technique but to a progressive and fatal accumulation of mutations. In summary, life eventually collapses.
When Cloning Backfires
The experiment began in 2005, nine years after Dolly’s cloning. The subject was a single female agouti mouse, whose somatic cells were used to produce the first generation of clones.
The process was then repeated with each new generation, like a “photocopy of a photocopy.” Initially, to the surprise of scientists, everything worked well. The first 25 generations of cloned mice developed normally, lived for about two years, and even showed a slight improvement in success rates.
It can be said without exaggeration that the idea of unlimited serial cloning seemed seductive. But nature, as always, had a different plan.
From the 25th generation onwards, something started to go wrong. Embryos developed less frequently, and the success rate of viable clones rapidly declined. By the 57th generation, success had become almost symbolic, with only 0.6% of attempts resulting in a birth, while the 58th generation did not survive for more than a day.
This phenomenon is explained by a silent, progressive, and irreversible accumulation of genetic mutations.
Accumulation of Mutations: A Fading Life
The team of scientists sequenced the genomes of cloned mice over generations, and the conclusion is clear. Each generation introduced around 70 new single nucleotide mutations (SNVs) and about 1.5 structural mutations (SV), such as chromosomal rearrangements or the loss of entire DNA fragments.
Between generations 23 and 57, the number of harmful mutations doubled. Chromosomal losses, translocations, and anomalies affecting essential genes appeared. This explains the embryonic failures, unsuccessful births, and the gradual collapse of the cloned lineage.
In the end, nature confirmed that cloning has an expiration date.
Why Sexual Reproduction is Essential for Species Survival
Despite the accumulation of mutations, scientists observed a remarkable phenomenon: the mice remained fertile. When clones from advanced generations were crossed with normal mates, the offspring exhibited normal birth rates, larger litters, healthy placentas, and, most importantly, a drastic reduction in transmitted mutations.
Sexual reproduction acted as a natural mechanism for genetic “cleaning.” What cloning could not correct, reproduction could.
“Beyond a certain number of generations, cloning inevitably leads to an accumulation of mutations that only sexual reproduction can eliminate,” explains Teruhiko Wakayama.
An Experiment Hard to Replicate
In total, over 1,200 cloned mice were involved in this experiment. An study that experts like Lluís Montoliu (CNB-CSIC) qualify as “heroic,” but probably impossible to reproduce due to its technical complexity and current ethical constraints.
In reality, this study also questions classic theories like the Red Queen hypothesis, which suggests that sexual reproduction is necessary to adapt to changing environments.
Here, under controlled conditions, without environmental pressures or external threats, cloning failed due to the inevitable mutations linked to the passage of time.
Human Cloning: A Limit not to Cross
This discovery reignites a longstanding scientific and ethical debate. For Sagrario Ortega, head of the mouse genome editing unit at CNIO, the conclusion is clear.
“Cloning is a valuable tool for research and biotechnology, but it should never be applied to humans. Nature always has a head start.”
And the evidence is clear: infinite cloning does not exist!
