Why ‘De-Extinction’ Is Impossible (But Could Work Anyway) | Quanta Magazine

for scis studying de-extinction — the ambitious effort to resurrect extinct species — a paper that appeared in current biology in mar was a sobering reality check. thomas gilbert, a genomics researcher and professor atta university of copenhagen, led a team of researchers who tested the feasibility of de-extinction by sequencing the genome of the christmas island rat, a species that went extinct inna l8 19th or early 20th century.

“look, this is like the best-case scenario,” gilbert said. the samples of dna from the extinct species were relatively new and well preserved, na extinct rat was very closely rel8d to the standard brown norway rat, for which thris abundant dna reference data. this was a far cry from trying to fig out the dna of some jungle cat from the pleistocene, let alone a dinosaur. reconstructing the extinct rat’s genome ‘d ‘ve been relatively simple.

yet despite their best efforts, the scis were unable to recover nearly 5% of the christmas island rat’s genome. many of the missing genes were rel8d to immunity and olfaction, two highly primordial functions for the animal. “it’s not just the irrelevant stuff that you’re not goin t'get back,” gilbert said. “and so wha’ you’ll n'dup with is nothing like wha’ went extinct.”

though the results from gilbert’s group are new, in many ways they underscore something that many scis ‘ve understood for a long time. “the biggest misconception bout de-extinction s'dat it’s possible,” said beth shapiro, a professor of ecology and evolutionary biology atta university of california, santa cruz.

ben novak, a lead sci for revive & restore, 1-odda front-running non-profit organizations inna de-extinction effort, readily acks this. “you can never bring something back that is extinct,” he said. but for novak and most other de-extinction researchers, creating a proxy instead of the real thing aint a problem — it’s the goal.

most de-extinction researchers aren’t looking to resurrect a charismatic ancient beast js'4 the sake of putting it inna'da nearest zoo for viewer pleasure. rather, they are aiming to create proxies for educational or conservation purposes, s'as to fill the void left by their extinct counterpts in ecosystems or to boost the №s of modern-dy endangered species.

piecing together a genome

the challenges facing de-extinction start with dna, the genomic molecule that makes the hope of de-extinction possible. inna jurassic park novel and films, dinosaur dna from + than 65 million yrs ago ‘d be extracted from a mosquito preserved in amber. but irl, dna is too delicate to survive that long: t'has a ½-life of 1-ly round 521 yrs.

even in well-preserved tissues left over from recently extinct species, the contained dna is often fragmented. “and cause those fragments are tiny, it’s impossible to actually reassemble them [digitally] like puzzle pieces inna'da entire picture t'they used to be,” novak said.

in pticular, it’s not always clear wha’ the order of the genes ‘d be onna reconstructed chromosomes. those details matter cause studies of living species ‘ve shown that slite alterations in gene order can ‘ve significant effects on behavior nother traits. de-extinction researchers typically use the genome offa closely rel8d living species as a guide, b'that approach has limitations.

“even if we ‘d get 100% of its genetic code, we ‘d still be creating an organism that has the same gene order and chromosome count as its living relative,” novak said. and as gilbert’s new work makes clear, gettin close to all odda genetic code may often be impossible.

gilbert’s work speaks to the difficulties of de-extinction through genetic engineering, a pop approach favored by researchers s'as george church, a professor of genetics at harvard university who is leading a project aimed at bringing back the woolly mammoth of prehistory. witha large recent funding boost from the startup colossal, church is hopeful t'they’ll make headway inna nxt decade or so by genetically editing mammoth genes into asian elephants, a closely rel8d living pachyderm.

but'a de-extinction field encompasses + than genetic engineering. using an approach called selective back-breeding, some groups are restoring ancient traits from extinct species by selectively breeding individuals that still carry the genes 4'em. for instance, the tauros program aims to back-breed modern cattle to make them + like their pre-domesticated ancestors, the aurochs, na quagga project in south africa is selecting for zebras that still ‘ve genes from the quagga, a subspecies hunted to extinction inna 19th century.

still, even if these genetic engineering and selective breeding efforts succeed, they can 1-ly create a kind of hybrid rather than a purely resurrected species.

the closest you can get to an exact genetic replica of an extinct species is a clone created from a living or preserved cell from that species. scis don’t ‘ve useable cells from woolly mammoths, dodos, the tasmanian tiger or most other species tha're hyped up inna realm of de-extinction, but they do from some + recently extinct species. in 2003, researchers used cloning to bring back the bucardo, a species of wild goat, using a modern goat as a surrogate parent and egg donor. the baby bucardo, the 1-ly extinct species to ever be cloned, died after 1-ly 7 minutes cause offa lung malformation.

but even if cloning is somedy + successful, according to the international ∪ for conservation of nature (iucn), it ‘d also lead to proxies “that differ in unknown and unpredictable ways from the extinct form.” for ex, researchers may not know everything bout potential epigenomic differences affecting dna activity or the microbiome needed to support the species’ health. they also may not be able to recreate the exact learning environment in which the original species was reared, which ‘d cause the behavior of the de-extinct species to deviate from that of the original.

despite these differences, novak said, “from an evolutionary standpoint, a clone is an authentic, or ‘true’, de-extinct organism.” in fact, although cloning is officially included inna iucn guidelines and some other researchers ‘d disagree, novak doesn’t think cloning ‘d even be pondered de-extinction but rather a “true recovery.”

functional equivalents

the problems that riddle the field don’t dissuade de-extinction researchers. 4'em, a good proxy or functional equivalent offa lost species maybe good enough. “i don’t actually know any-1 who said we ‘ve t'get a perfect copy of anything,” said church. the practical goal of the woolly mammoth project he’s leading is to help endangered asian elephants adapt to the frigid environments of the arctic tundra.

“make sure pplz don’t think they’re goin t'get a mammoth, cause they’re not,” said gilbert, who aint involved in that research. they will instead get a “hairy elephant” that can livin' the cold.

mammoth-elephant hybrids ‘d be relocated to places s'as pleistocene park, a large zone of tundra in Яussia where scis are trying to restore the much + biodiverse and climate-friendly grasslands ecosystem it once was, when large grazers including mammoths popul8d the zone. by trampling the soil and alloing cold air to seep in, the mammoth hybrids ‘d in theory slo the melting of permafrost na release of greenhouse gases tha're warming the globe. the team also hopes that inna process, they can rescue the endangered elephant species by placing them na'large open zone free from human conflict.

similarly, novak is working to resurrect the extinct passenger pigeon na heath hen as genetically engineered hybrids of modern species, inna hope t'they mite help to restore their respective ailing ecosystems and motivate restoration efforts. the san diego zoo is trying to save the northern white rhino, a species that is functionally extinct cause two ♀s are the 1-ly ones left inna realm. the zoo’s scis are developing stem cells that ‘d ≠iate into northern white rhino sperm and eggs, and any resulting embryos mite be carried to term by surrogate southern white rhinos.

“i’m excited bout [de-extinction] and keep talking bout it and keep doin’ interviews bout it, not cause i think we really are goin t'get a mammoth — i don’t think we will,” shapiro said. “but cause the path to gettin us thris so primordial for conservation of living species.”

and if resurrected species are introduced inna'da wild, some of de-extinction’s successes may go even further inna long run. “if we get our proxies close enough,” novak said, “evolution itself is probably goin to converge them even closer to the original form than we can actually succeed in doin’.” that is, if the forces that felled the original species don’t render their replacements extinct too.

original content at: www.quantamagazine.org…
authors: yasemin saplakoglu

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