LONG-GONE species like the woolly mammoth, Tasmanian tiger, and dodo bird could return from the dead as part of a “de-extinction” campaign.
The term “extinct” brings to mind ancient heavy-hitters like the mammoth and dodo, but scientists are working to bring back nearly every animal under the sun.
This includes a rodent often excluded from the conversation: the Christmas Island rat.
The creature is named for its place of origin, a chunk of land off the coast of Australia, where it developed strong teeth to feast on crabs.
The rodent was lost over a century ago when Europeans sailed to Christmas Island and introduced novel diseases.
De-extinction can be complicated. Its success hinges on the recovery of undamaged, complete DNA sequences.
But the best-preserved remains don’t always have the best genetic starting materials.
Such is the case with mammoth carcasses found encased in ice. The extreme chill can render irreparable damage to DNA.
However, with the Christmas Island rat, which went extinct in 1903, scientists seem to have struck gold.
A study published in Current Biology in 2022 lays out a case for resurrecting the rodent.
A team in Norway has managed to obtain almost all of the rat’s genome, but that’s not all.
Because it diverged from surviving species fairly recently, the Christmas Island rat shares about 95% of its genome with the common brown rat.
Since some genes, like the gene that codes for sense of smell, are impossible to recover, scientists won’t be able to generate a perfect replica.
The remaining DNA must be sequenced, meaning scientists must determine the order of the four chemical building blocks called bases.
Once scientists have figured out the pattern of these amino acids, they can compare it to the reference genome of the living species.
Hypothetically, all they must do is identify the parts of the genomes that don’t match up and edit the DNA of the living species to match that of the extinct one.
Scientists have yet to recreate a full genome of an extinct species, so an identical match seems unlikely.
The best results will be a cross between alive and extinct species with a high degree of genetic similarity – but this proves more difficult in some species.
The quest to bring back the woolly mammoth likely won’t start with a clone.
Colossal Biosciences, a multi-million-dollar biotech firm based in Texas, is devising a way to bring back the megaherbivore.
The firm has obtained more than 60 partial woolly mammoth genomes, which will be used to edit elephant genomes in the lab.
Once scientists have settled on a DNA sequence, they will implant a hybrid elephant-mammoth embryo into an Asian or African elephant.
The company plans to produce its first calves by 2028 and frames de-extinction as a noble effort to correct past mistakes.
“For the first time in the history of humankind, we are in control of a science with the power to reverse and prevent biodiversity loss on a large scale,” reads a statement on the company website.
“We can heal a hurting planet. We can protect the species living on it. We can ethically decipher and protect genetic codes. And we can begin to turn the clock back to a time when Earth lived and breathed more cleanly and naturally.”
Another animal Colossal hopes to resurrect is the dodo, an ill-fated flightless bird last spotted in 1662.
The dodo was native to the island of Mauritius in the Indian Ocean. Isolation meant they had no natural predators – until settlers arrived.
Humans hunted the birds for their meat and introduced non-native animals that ate their eggs and outcompeted them for food.
Flightless and slow to reproduce, dodos were especially vulnerable, and humans succeeded in wiping them out in just a few decades.
Some naysayers argue the poorly-evolved birds were doomed from the start. However, scientists believe they were perfectly suited to their environment and could even outpace a human over rocky terrain.
Now Colossal is aiming to bring this famed species back from the dead.
Last year, the firm reached a key milestone by fully sequencing the dodo’s genome from remains in Denmark.
The next step was to compare the genetic information with the dodo’s closest relatives in the pigeon family.
Their target, the Nicobar pigeon, is an island-dwelling species with brilliant plumage.
Scientists must remove primordial germ cells from an egg and edit them with the desired genetic traits in the lab.
Once this process is complete, they will inject them into an egg at the same developmental stage, which will give rise to hybrid offspring.
This is hypothetical, of course – scientists have yet to see how the process will pan out.
Colossal also aims to bring back the thylacine, a marsupial native to Oceania.
The thylacine, also known as the Tasmanian tiger, is one of the only extinct species we have surviving footage of.
The long, lanky marsupial had several signatures including a thin tail, striped lower back, and narrow snout.
Like the dodo, humans played a key role in the thylacine’s demise.
The last captive specimen died in September 1936, purportedly from neglect, after being locked out of its sleeping shelter and exposed to freezing temperatures.
In 2022, Colossal announced a partnership with an Australian lab that pledged to de-extinct the thylacine and reintroduce it to the wild.
So far, this project has proven more feasible than reviving the woolly mammoth.
Marsupials are also born halfway through mammal embryogenesis, with development finishing in the mother’s pouch.
In contrast to the months a mammoth must spend in the uterus, the thylacine only needs a few weeks.
As Colossal leads the charge, a question remains: what are the outcomes of reintroducing an animal after its ecological niche has vanished?
In the case of the woolly mammoth, some scientists believe the creature could mitigate climate change and find a role in the Arctic ecosystem.
Thousands of years ago, the huge herbivores prevented shrub and tree growth as they trampled the Earth, also serving as pollinators as they spread seeds in their dung.
The Arctic terrain has grown mossy and waterlogged in their absence. However, it is unclear if there is space for them in this unfamiliar environment – not to mention the possibility of causing more harm than good.
Rather than mitigate it, mammoths could contribute to global warming by eroding the permafrost during the warm season and releasing methane.
A team of researchers penned a 2017 article in Nature that questioned spending on de-extinction efforts when the same resources could be put into preserving living species.
The authors noted that “public funding for conservation of resurrected species would lead to fewer extant species that could be conserved, suggesting net biodiversity loss.”
The only solution would be to fund both efforts equally, they concluded – but opportunity costs would likely outweigh any benefits.
“Potential sacrifices in conservation of extant species should be a crucial consideration in deciding whether to invest in de-extinction or focus our efforts on extant species,” the authors wrote.
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