So, you know the movie where Batman fights Wolverine and then   David Bowie accidentally  invents a cloning machine.

What was that called? Oh right, The Prestige.

Spoiler alert for a movie that came out  in 2006, but Hugh Jackman’s character   basically clones himself over and  over again as part of his magic trick. But it’s not necessarily, like, cloning himself originally. It’s like clones of clones of  clones of clones of clones.

In the real world, making a copy  of a copy of a copy of, like,   a photocopy or something,  eventually leads to disaster. But how many times could  you actually clone yourself? How many generations of “you”  could you make if you had,   the absolute biggest ego known to humankind.

Well science is already testing these limits. At least in mice. And in a landmark paper published in 2026,  one team set a new record of 58 generations.

But as they kept pushing,  things started going south. So let’s take a look at what  happens when you clone a clone. [♪ INTRO] In 1903, a plant physiologist named  Herbert Weller argued that…due to   advances in horticultural science…we  needed a new set of standard terms. He introduced the term clone, which  he took from the Greek “klon,”   meaning "twig" or another plant cutting.

At its most general, the word  refers to genetically identical   copies of DNA sequences, living cells,  or whole organisms created asexually. When someone takes a cutting  from their bestie’s plant    to grow their own at home, they’re creating a clone. So humans have been cloning things  long before the jargon existed.

Meanwhile, animals have been cloning  themselves long before humans did it for them. A few species are known to reproduce clonally…  from certain flatworms to starfish to lizards... through the regeneration of a body  part or so-called virgin birth. Yeah.

Sometimes just one body part, like  a limb or tail, provides everything   an animal needs to build all the tissues  and structures in the rest of the animal. Humans are cool, but we can’t grow a whole  body from a decapitated head…or like,   grow a head back on a body that  doesn’t have a head anymore. We do know a thing or two about  artificial cloning, however.

The applications of which range  from cultivating organs tailored   for transplant recipients, to growing  synthetic meat, to species conservation. All of these applications  are either already in use,   or in various stages of research and development. Each has its own benefits and drawbacks.

And yes, the ethics are  being passionately debated. Even before you get into the quagmire  that is cloning entire humans. Meanwhile, the methods used  to create animal clones have   varied widely over the years… including  years before Weller coined the term.

But generally, the first era of cloning  research required embryonic cells. More specifically, an embryo  that was just a few cells big. Because at that point, each of those cells has  the unique ability to develop into any tissue.

Which you kinda need if you want to grow a  whole body with lots of specialized parts. If you want to clone an animal from an older,  specialized cell, you’d have to find a way   to reprogram it…get it to revert back to its  “I can grow up to be whatever I want” stage. It was hard enough getting a clone  from an embryo that was too old.

Cloning an adult animal was  a whole ‘nother can of worms. But over time, scientists made more  and more tweaks to get their methods   to work on more and more highly specialized cells. Which brings us to a baby  sheep named after Dolly Parton.

In 1996, Dolly became the first fully  developed mammal cloned from adult tissue. Specifically, a cell from a mammary gland. Although, technically, she wasn’t a full clone.

It’s perhaps more accurate to call her  a chimera, since scientists later found   the mitochondria in her cells came from  the enucleated egg cell she grew from. Not the cell from which her DNA was taken. Also, it’s worth noting that  there were 276 failed attempts   at the same experiment before Dolly was born.

But Dolly was certainly a success. She lived long enough to naturally  conceive through sexual reproduction,   and gave birth to six lambs. As far as we know, no one  tried to clone Dolly herself.

But that doesn’t mean scientists haven’t  done that for other cloned adult animals. Up until 2004, serial cloning  had only been done in mice. But that year, scientists published a paper   describing their successful cloning  of a bull to the second generation.

This was a continuation of a study  first published in 2000, in which a   group of researchers cultured skin cells from a  generation-zero Japanese beef bull, transferred   the nuclei into fertilized eggs, and implanted  the resulting embryos into surrogate cows’ uteri. They ultimately produced six cloned  generation-one, or “G1” calves. The 2004 publication described producing one  healthy surviving G2 from one of the G1 calves.

This challenged the belief that mammals  need sexual reproduction to propagate   their genetic lines through multiple generations. That said, when the team attempted G3,   only about 20% of the attempted embryo  transfers reached the fetus stage. And all of them spontaneously aborted.

Still, researchers were tenacious, and the  G3 threshold in mammals was soon crossed. And G4. And G5… By 2013, a mouse experiment that began in  2005 had gone on long enough to reach the   25th generation milestone, with  almost 600 new mice generated.

One big reason for the researchers’  success was they identified chemicals   that worked wonders in reprogramming  and reverting a specialized cell. If a cell has a certain job in your body,  it’s going to be physically different in   structure and composition than  cells that do any other job. It also has modifications to the  genetic instructions inside it,   including small chemical tags that  accumulate on the DNA molecule,   and the way that DNA is packaged  inside the cell’s nucleus.

To reprogram a cell back into an immature state,   you need a way to both remove those tags  and reconfigure how the DNA is packaged. Only then will it be able to give rise to all  the tissues you need for a whole new body. Scientists can use chemicals  called small molecules… yes, that is really what they’re called… to  slip into a cell and mechanically tweak   those structural differences  back to the embryonic stage.

But in addition to some particularly  well-chosen small molecules, the team   also benefited from using a specific type  of cell to make their clones: cumulus cells. Cumulus cells are a specialized adult  cell that help eggs mature and ovulate. Just a few years before their study began,  other researchers discovered the nuclei are   easier to reset than other kinds of  specialized cells, like skin cells.

By G25, experiments suggested the clones  were fertile and could reproduce sexually. The team also noted the success rate   didn’t clearly decline from the  first to the 25th generation. Instead, it fluctuated.

And while there were some  genetic errors that popped up,   they weren’t all harmful, and didn’t  seem to accumulate in irreversible ways. The scientists cautiously figured if they could   just get all of the conditions correct  each generation, it could go on forever. But they knew that was a very big “if”.

With all the tips and techniques  they had gleaned over the decades,   the study that started in 2005  continued all the way to 2026,   producing a record-breaking 58 generations of  mouse clones, and more than 1,200 mice in total. That’s when the ultra-complicated  hurdles became too high to clear. Basically, from generation 25 onward,  the success rates of producing live   cloned pups trended downward, and  by 58, it dropped to almost zero.

The researchers couldn’t identify  one single point of failure. It was more or less due to  the gradual accumulation   of various genetic mutations and the  resulting problems with cell division. Scientists use the term mutational load to refer   to the number of harmful mutations that  accumulate from generation to generation.

And generally speaking, that  load is far higher in serial   clones than sexually reproduced individuals. That’s because, in sexual reproduction,  as egg and sperm cells are created,   each receives a unique, shuffled  version of half an animal’s genome. It’s half because that’s part of  the nature of being a sex cell.

And it’s shuffled thanks to a process the  chromosomes go through called recombination. Scientists are pretty sure it’s recombination  that randomly breaks up harmful mutations. Basically, there’s always some chance a  given genetic error in an animal’s full   genome won’t end up in the sex cell  that then goes on to make a baby.

Cloning skips all of this beneficial shuffling. For example, after the 25th generation,   the genetic errors began to affect  larger chunks of the genome. These larger errors eventually became deleterious…  they made it more likely for the mouse to develop   a disease or disorder… to the point that  the next generation was no longer viable.

Another issue was that the placenta was  often abnormal in later generations. And without a healthy placenta, it’s  harder to bring a healthy pup to term. But the researchers remain  cautiously optimistic that,   with a better grasp on all of the factors,  serial cloning might continue indefinitely.

Which is either miraculous or disastrous,   depending on your outlook and  preferred subgenre of science fiction. So what does all of this mean? Well, the authors say their results  contradict the Red Queen Hypothesis,   which holds that sexual reproduction is necessary  to increase genetic diversity and propagate.

Instead, they found making a copy  of a copy of a copy can introduce   genetic mutations that don’t harm the offspring. And that counts as diversity. But they also note their work  supports Muller’s ratchet theory,   which posits that, without recombination,  generation after generation of asexual   reproduction will eventually build up so many  mutations, the clonal line will go extinct.

However, if you look to nature,  this isn’t necessarily the case. One species of fish in the Amazon  has obviously found ways to get   around the ratcheting. It has been  successfully cloning itself as its   only form of reproduction for  roughly the past 100,000 years!

But those are fish. Not mammals. So as far as we know, Muller’s ratchet theory  holds for mice, the family dog, Hugh Jackman,   and any narcissist billionaire that  thinks he can achieve immortality   by transferring his consciousness  into clone after clone of himself.

Sorry, I should not be giving them ideas. [♪ OUTRO]