Reviving extinct animals: in the future, there will no longer be mammoths but “mammophants” | science and technology

The skeleton of a mammoth is prepared for an exhibition in Barcelona.Gianluca Battista

“I would pay dearly to see a furry, half-elephant mammoth in a zoo or wildlife park, even knowing it’s not genuine,” exclaims geneticist Tom Gilbert. “But it would be a mistake to call it a mammoth.” His team at the University of Copenhagen has just published a study that explores this idea: we will never have a mammoth like the ones that grazed millions of years ago during the Ice Age. None of the extinct species his team is trying to revive will be the same. Tasmanian tigers, passenger pigeons and dodo birds will all be hybrids, a mix that resembles their extinct counterparts.

The fact does not bother Harvard scientist George Church. “No surprise,” he said. The researcher spent a decade working to revive the mammoth. To do this, he has just raised more than 14 million euros in his new company, Colossal. “We are not working to bring back an extinct species, but to bring back extinct genes and test their resistance to cold,” he explains to EL PAÍS. “The principle is not to make perfect photocopies, but selective and diverse hybrids, with modern, ancient and synthetic DNA,” explains Church. He’s not looking for a mammoth, but an Asian elephant with a handful of mammoth genes that allow him to withstand polar temperatures, as well as other traits that improve his adaptability, including resistance to modern viruses. Could it be a mammoth? Would it no longer be extinguished?

Colossal’s web page, which is looking for investors, talks about “resurrecting the mammoth”. But many specialists prefer to call it a mammophant, because it will have characteristics of both animals. Church wants to create a being that fulfills the ecological function of the mammoth to help fight the climate crisis. Should we manufacture genetically modified species that are useful to us? “I think we are designing all kinds of hybrids,” replies the synthetic biology expert. “We’ve done this before on purpose and without realizing it, and these hybrids are a common way to create new species and new functions during evolution.”

Church’s technique is the most sophisticated of three possible techniques that have been used for years in attempts to recover missing animals. The simplest is selective breeding, a technique that has long been used to promote more desirable traits in domesticated animals and in this context seeks to reclaim traits from an ancestral animal. Scientists have done this with cows, seeking to recover aurochs, and zebras, whose ancestor is the quagga.

The second technique is cloning. Since the 1996 cloning of “Dolly” the sheep, the same technique has been used with the DNA of extinct animals. This technique enabled the first and, so far, only successful attempt to resurrect an extinct species. Technicians from Aragon have managed to recover Célia, the last ibex of the Pyrenees, a mountain goat that disappeared in 2000 after decades of hunting. Celia’s clone was born with a lung defect that suffocated her less than ten minutes after birth.

The third de-extinction strategy is gene editing, the most promising due to technological capabilities to rewrite DNA. In gene editing, the DNA of the old animal is “copied and pasted” onto an existing animal, the most similar animal possible. This is what geneticist Tom Gilbert attempted in his recent study, which took a rat as the subject.

The Christmas Island rat became extinct in the late 20th century after coming into contact with diseases transmitted by European rats. For Gilbert and his team, he is an ideal candidate to analyze how far they can go with the technique they will use with mammophants. By analyzing how much of his genome they could salvage, they discovered that 5% of his genome differed from that of a similar modern rat.

“Imagine giving you a fragmented book in medieval English and asking you to compare it with a modern English version of the same book. Much of it will be recognizable, but some words will have changed so much that you won’t be able to identify them. This is our basic idea”, explains Gilbert.

This missing 5% is not in random points, but in concrete elements. For example, the genes that define his sense of smell cannot be retrieved. If the team were to resurrect him, the rat would not be able to smell like the original, which would change his relationship with the environment and other animals. “Some of the most important genes that made the Christmas Island rat unique are irrecoverable. It is almost impossible to hope to completely recreate an original species,” Gilbert summarizes.

Although Church is clear that he only needs to replicate some characteristics of the mammoth, he is confident that improvements in gene sequencing will address these shortcomings in the near future. “It took 2001 to 2021 to complete the remaining 5% of the human genome,” Church recalls, “and as we continue to sequence genomes like humans and rats, we will continue to improve and eventually we will get complete and precise olfactory genes.”

Christmas rats and blue butterflies

That doesn’t seem to be a problem for expert Beth Shapiro, who worked on recovering the genome of the mythical dodo bird and now the carrier pigeon, which went extinct after being widely hunted in the 20th century. “No one is suggesting that the only possible path is to create something that is identical to a specific organism that once lived. That is not the question, ”explains the researcher from the University of California. The goal of those who work for deextinction is “to recover particular characteristics, particular roles, which can help to reestablish the links between organisms that live in communities. To do this, a perfect genome is not necessary,” says Shapiro, author of How to Clone A Mammoth.

Barcelona-based evolutionary biologist Carlos Lalueza-Fox doesn’t consider recovering the woolly mammoth “feasible” due to the technical complexity of the challenge. Genetic manipulation and experiments on embryos have developed mainly with laboratory animals. That’s why Lalueza joined Gilbert in trying to resuscitate the Christmas Island rat – or another candidate whose DNA they already have: they have just sequenced the genome of the blue butterfly Xerces, which disappeared in the middle of the 20th century in cause of urban development in San Francisco. . “An insect and a rat is more feasible, but because the mammoth is more spectacular, they chose a target that would allow them to raise more money,” explains Lalueza, author of the book. Extinctions and researcher at the Institute of Evolutionary Biology at Pompeu-Fabra University. Gilbert clarifies that he is not against these de-extinctions, but he wants their backers to understand what they will be getting.

The project which aims to resurrect the thylacine, or Tasmanian tiger, a legendary Australian marsupial, has just received 4.5 million euros in investment from a philanthropist who discovered it on YouTube. It is led by Andrew Pask, who in 2017 published the animal’s genome, which he called “the best of all extinct animals”. Pask thinks Gilbert’s conclusions are overstated and don’t apply to all species. Pask’s thylacine project will use the bush rat as a genetic model.

Pask acknowledges that it’s worth asking what the outcome of his work will be. “This raises an interesting debate. If you use filler DNA in the genome of an extinct animal to complete it, what would that mean for that species? »

Church initially believed his team would reach their goal within decades, but with the millions raised, he sees the goal getting closer to the six years his business partner promises. (An elephant’s gestation alone takes about 20 months.) And Church acknowledges that he still doesn’t know how much they’ll need to modify the Asian elephant. The species are separated by half a million genetic differences, but for Church, a few dozen changes in DNA could be enough. The goal isn’t to trace all the differences, but to get the 50 characteristics his team picked out as necessary for the new animal to move through the frozen tundra like a fish through water.

Return to their natural habitat

According to Shapiro, it all comes down to how the specimen interacts with the ecosystem. None of these projects aims to produce specimens for display in museums or cages, but to fulfill their function in the wild. “Anyone who works on serious deextinction projects does so with the goal of creating a substitute for extinct species, reconstructing and reviving extinct features, creating new organisms that can replace extinct ones, and allowing these new organisms to revitalize and, in some cases, restore ecosystems that have not yet adapted to the loss of this extinct species,” she explains.

Pascal agrees. “The rationale for doing this with thylacines is to put them back into the ecosystem and back to their natural habitat.” That’s why he’s championing the resurrection of the thylacine: its habitat in Tasmania has remained almost the same as before, providing the perfect environment to reintroduce it and benefit the whole ecosystem.

All de-extinction projects come up against significant ethical, legal and political issues. But these five synthetic biology specialists are convinced that they will develop tools that will also help save endangered species. Pask says his advances will be “immediately” applied to conservation science, “particularly our work on stem cells, gene editing and surrogacy, to help the breeding programs of other marsupials.” And Church insists, going even further, that “when we talk about losing cash, we rarely mention that at the same time, we could gain cash faster.”

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