Defector, mostly a sports-and-social-commentary outlet, asks a scientific question: We’re now at a point, genetics-wise, where we’re ready to make de-extinction a real thing. But if reconstructed species are only imprecise genetic replicas of the original species, why would we be doing that?:
When Thomas Gilbert, a genomics researcher at the University of Copenhagen, sat in at some of the first de-extinction meetings at National Geographic in 2012, he remembers a brainstorm of what species the efforts should focus on. Suggestions of mammoths, Steller’s sea cows, and woolly rhinos were all met with lots of attention. “Then I go, ‘Christmas Island rat,’ just to see what happens,” Gilbert said. “And it was just like, dead silence.”
A few years later, Gilbert, still thinking of the rat, had an idea. The creature seemed the perfect guinea pig for a test of the limits of de-extinction technology. The species had relatively well-preserved DNA, and he guessed the rat had diverged from its surviving relatives just a few million years ago—by comparison, mammoths and Asian elephants diverged around 5 million years ago. And the Christmas Island rat’s close relative, the Norway brown rat, also happens to be a lab animal, meaning its genome has already been extensively sequenced and edited. So Gilbert and a team of researchers used computer models to reconstruct the Christmas Island rat’s genome to see how close their proxy could get.
The researchers extracted DNA from two Christmas Island rat pelts collected at the turn of the 20th century and sequenced the samples over and over to retrieve the genome, according to their paper in Current Biology. Old and degraded DNA survives in short fragments, excluding the possibility of assembling the entire genome from scratch, or what is called a de novo assembly. Instead, the researchers mapped these small fragments onto the genome of the closely related Norway rat, from which the Christmas Island rat diverged about 2.3 million years ago, according to their estimate. This mapping is likely the only way to approach the genomes of many extinct species, Gilbert said.
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For 1,661 of the genes, the researchers only recovered about 90 percent of the sequence, meaning they could not fully reconstruct the original genes. And 26 genes were missing entirely. The researchers suggested they could recreate the Christmas Island rat’s overall appearance, such as the rounded ears and thick black hair. But the missing parts of the genome contained important immune and olfactory genes that influence the rat’s ability to forage, detect predators, or track down mates. Losing these genes would probably affect the recreated rat’s ability to survive in the wild.
As Gilbert sees it, the point of this paper was not to be judgmental, but to show that it’s possible to predict how good a proxy scientists would be able to make, “so people know what they could end up with,” he said. “And decide if they are happy with that in light of resources invested.”
If an exact replica is out of reach, what then becomes the goal? How close must a proxy be to the original species to earn the vaunted title of mammoth or dodo?
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Consider the clone of Celia, the only arguably successful de-extinction, who was born and died on a single summer’s day in 2003. Celia was the last bucardo, a wild goat with gently curving horns that once roamed the Pyrenees before hunters drove the species to extinction. Several months before the original Celia was crushed to death by a falling tree in 2000, scientists had preserved some of her cells. They injected the nuclei of Celia’s cells into domestic goat eggs that had been vacated of DNA, and then implanted the eggs into surrogate mothers. After 57 implantations and seven pregnancies, six ended in miscarriage. One mother, a hybrid between a goat and a Spanish ibex, carried Celia’s clone to term in a caesarean section. As Carl Zimmer reported for National Geographic, the newborn bucardo “was struggling to take in air, her tongue jutting grotesquely out of her mouth.” A necropsy revealed a malformed lung; she lived for 10 minutes.
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Announcement notwithstanding, there is no objective calculus of how many suffering creatures is “worth” one healthy one. Colossal plans to develop a proxy mammoth out of Asian elephants, which are endangered. The first genetically edited mammoth calves will be carried to full term by surrogate elephant mothers, [Colossal co-founder, entrepreneur Ben] Lamm said. An elephant cannot consent to becoming a surrogate mother for another species, a pregnancy likely to come with complications, as woolly mammoths are larger than Asian elephants.