July 13, 2024

I, Science

The science magazine of Imperial College

‘De-extinction’ scientists are trying to bring back dead species, but some have raised concerns about these efforts

We are living through the greatest mass-extinction event since the dinosaurs died out. Dozens of animal and plant species disappear every day. While conservationists work hard to save our remaining biodiversity, a few scientists around the world want to go further. They are attempting ‘de-extinction’: bringing back species from the grave.

Recent advances in genetic engineering, especially the advent of quick and easy genome editing, have moved the concept of de-extinction abruptly into the realm of possibility. The question is no longer can we, but should we bring back species of the past?

“It gets a cautious yes from me,” says Helen Pilcher, British author of the book Bring Back the King: The New Science of De-extinction. She sees in de-extinction the potential for a powerful conservation tool, if the revived species contribute positively to their ecosystem, but warns about the uncertainties involved:

“We need to think about the possible repercussions of introducing a species back into an ecosystem that it hasn’t seen for a long time, so hopefully there aren’t any surprises. I don’t think it’s ever something we should be gung-ho about, or rush into.”

Not everyone thinks that it’s a useful conservation strategy. In fact, some think it does more harm than good. Ecologist Joseph Bennett, from Carleton University, in Canada, argues that de-extinction projects are too costly and uncertain in their outcome to be justified, given the urgent need for funding the preservation of living species.

In a recent study published in Nature Ecology and Evolution, Bennett and other experts conclude that de-extinction is a poor investment, if the goal is to promote biodiversity. In one scenario, where the money is detracted from other conservation efforts, the researchers predict that attempting to revive dead animals could actually lead to a net loss of species.

“You would be better off spending your resources on living species, of which there are many that need conservation,” Bennett says. “Given that the resources could be used elsewhere, it would be a one step forward, two steps back scenario.”

Splashing out on the resurrection of a single species may be justified if their role in the ecosystem will be beneficial to many others. This is the argument for bringing back the passenger pigeon, a nomadic species of Northeastern America which lived in flocks numbering thousands of individuals, until we shot the last one in the late 1800s.

taxidermy passanger pigeon

The extinct Ectopistes migratorius, or passenger pigeon, James St. John

When passenger pigeons came in to a forest to roost, they would wreck the place: branches were broken, saplings toppled, and the forest floor was covered in a thick layer of droppings. From this apparent devastation, life flourished: sunlight penetrated the woodland floor, which would be nicely fertilized for new plant growth, in turn attracting all kinds of animals. Ecologist Ben Novak thinks bringing back this process could save many of the endangered forest species of the Eastern United States.

The organisation he works with, Revive & Restore, is a California-based non-profit attempting to enhance biodiversity through ‘genetic rescue’ of endangered and extinct species. Novak is on track to bringing back the passenger pigeon within a few years by editing the genome of its closest living relative, the band-tailed pigeon. With assisted reproduction, he plans to boost numbers back to their thousands.

“The passenger pigeon was a forest engineer,” he says. “In its abundance, it was creating forest cycles of regeneration which benefited hundreds of species in the Eastern United States. Those cycles are no longer occurring on a regular basis, outside of what limited human management is going on. The self-sustaining, renewable and cheapest solution over the centuries is a flock of pigeons—this really is about creating a biological entity that serves our long-term conservation goals.”

Bennett, whose job it is to scrutinise these claims, remains unconvinced. For him, de-extinction could only be justified if the cost, the chance of success and the role of the species are all well-understood, and balance out. “It’s hard to see that that is indeed the case,” he says. “Is anything living now that is dependent on the passenger pigeon? No.”

Despite Bennett’s maxim that we should focus on helping the living and not the dead, this distinction is not always clear-cut, says Pilcher. If she could ‘bring back’ an animal, she would choose one that is still with us today: the northern white rhino. There are only three individuals left, and they are “too related, too old and too sick” to reproduce, she says. “They’re walking dead. They may as well be gone.”

De-extinction techniques, such as stem cell biology and assisted reproduction, could be used to bring back this species from the brink. That’s why people like Novak and Pilcher favour the phrase ‘genetic rescue’—it can be applied equally to extinct or endangered species.

The science is still young, and besides the cost, there are ecological and ethical concerns. De-extinction will have to prove its worth before it is widely accepted among the solutions to our biodiversity crisis.

Bruno Martin is studying for an MSc in Science Communication at Imperial College London

Banner image: DNA concept, Natali_Mis