Species Extinction is a Growing Threat
A 2019 United Nations report from the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES) strikes a major warning for the future of biodiversity on earth: as many as one million species are presently under threat of extinction, and many of these could cease to exist within decades.
In response, many scientists are proposing stepping up efforts to bring back extinct species, a de-extinction approach known as resurrection biology.
How Does De-Extinction Resurrection Biology Work?
Broadly speaking, lab scientists pursuing the goal of resurrecting lost species rely on two different approaches:
- Back Breeding
Back breeding (also known as backpropagation) relies on identifying a plant or animal species that is closely related to the extinct one – and breeding those specimens that exhibit characteristics of the lost species. Among the most famous examples is the work of the Heck brothers in Germany, who sought in the 1920s to resurrect the lost Auroch (the ancestor of modern cattle) that went extinct in 1627.
- Genetic Engineering
The development of modern genetic analysis techniques has given biologists the hope of finding and extracting viable DNA samples from long-lost species in hopes of bringing them back to life. As we’ll see below, this process is rarely straightforward and may involve copying unique genetic characteristics from the recovered DNA and incorporating them (using CRISPR CAS-9 technology) into the DNA of closely related species capable of producing viable offspring.
Recovering the American Chestnut Tree: Unfortunate Pitfalls Along the Way
For decades, researchers have been diligently trying to backbreed various species of chestnut trees (mostly disease-resistant Asian varieties) to recreate an improved version of the American chestnut, a highly-prized tree that was effectively wiped out by the arrival of the chestnut blight fungus (Chryphonectria parasitica) from Asia.
The American Chestnut Foundation (TACF), which had been supporting efforts to re-create the American chestnut, was poised to begin re-foresting efforts with the genetically engineered, disease-resistant variety, known as Darling 58, created by the State University of New York College of Environmental Science and Forestry (SUNY ESF) when a mistake was identified. Somewhere along the line, the incorrect variety was propagated, and/or a gene insertion had gone wrong. TACF abruptly canceled the tree distribution project, which may have to go back to square one, which would be a huge setback for those eager to see majestic American chestnuts return to the North American landscape.
Recovering Lost Mammal Species: DNA Recovery is Harder than First Thought
Excitement abounded in the field of resurrection biology back in 2013 when Revive & Restore’s founders, the husband and wife team Ryan Phelan and Stewart Brand, presented their seminal TED talk announcing the brand-new dawn of the de-extinction era.
Hopes were high that many prominent extinct species could be revived, such as the wooly mammoth, Siberian tiger, Passenger Pidgeon, Tasmanian tiger, Pyrenean ibex, and the Dodo.
Scientists at the time were encouraged by the DNA cloning of Dolly the Sheep by Scottish researchers in 1996, which marked the first successful cloning of a large mammal through genetic engineering. If that was possible, the thinking went, it could be possible to collect ancient DNA, amplify it in a PCR machine, and inject it into the DNA of an embryo from a similar species that could bear the offspring.
Such was the approach taken by Australian researchers attempting to bring back the marsupial Tasmanian tiger (thylacine), which went extinct in 1936. However, the recovered DNA (from a thylacine specimen preserved in 1886) ultimately proved too degraded to create a successful clone.
Efforts to revive the long-extinct woolly mammoth took a more intensive technical approach. In 2013, Russian scientists announced they had recovered female woolly mammoth blood and tissue samples on the Siberian Lyakhovsky Islands.
Working under the assumption that the Asian elephant is the closest living relative, researchers used CRISPR/Cas9 technology to add genetic features characteristic of woolly mammoths (such as their impressively thick fur) to the genes of the Asian elephant embryo in hopes of producing a hybrid offspring that looks like the lost woolly mammoth.
After nearly a decade, neither the Russian efforts nor the work of Revive & Restore’s Woolly Mammoth De-Extinction project had produced a viable result. In 2021, the Dallas biotech firm Colossal, founded by the outspoken George Church and entrepreneur Ben Lamm, took over the latter project. Since that time, Colossal has raised hundreds of millions of dollars towards reviving both the woolly mammoth and the marsupial thylacine – promising to deliver viable results by 2028.
Rhesus Monkey Cloning Research Reveals Underlying Difficulties in Using Recovered DNA to Resurrect Species
A better understanding of cloning may help further the goals of resurrection biology.
Chinese laboratory scientists at the Institute of Neuroscience, Center for Excellence in Brain Science and Intelligence Technology in Shanghai have been able to clone two different macaque species: a rhesus monkey and a pair of cynomolgus monkeys. The success rate of cloning remains very low, with many attempts required before a single live birth; however, the Chinese researchers identified a problem in the developing placenta, which they addressed by transplanting the cloned cells into a non-cloned embryo, which developed normally.
Advances in cloning monkey species could not only help improve the success chances of resurrecting extinct species, but they could also help provide a consistent supply of monkeys suitable for animal research.
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