This week, scientists announced a breakthrough in the battle to bring the northern white rhino back from the brink of extinction.

The last male of the species died earlier this year, reducing the entire population to just two female animals beyond their calf-baring years. But now, cutting edge reproductive and stem cell technology has produced embryos from frozen northern-white sperm and the eggs of the closely related southern white rhino.

"These are the first in vitro produced rhinoceros embryos ever. They have a very high chance to establish a pregnancy once implanted into a surrogate mother," Thomas Hildebrandt, one of the scientists behind the project, said in a press release.

The news offers tantalizing hope that scientific advances might right past wrongs, giving creatures wiped out by humans a second chance.

But just because we can do something, does it mean that we should?

Pleistocene Park

Scientists have already created embryos with genetic material from the recently extinct gastric brooding frog, and in 2003, a clone of the last female Pyrenean ibex was born to a goat — though it only survived a few minutes. 

But they're also setting their sights creatures that haven't walked the earth for hundreds, or even thousands, of years.

Researchers have successfully decoded the entire genome of the Tasmanian tiger, which was last seen alive in 1936, and hope to be able to edit its genes into the egg cells of a surviving marsupial such as its diminutive cousin, the numbat.

And a team at Harvard University is working to bring the woolly mammoth back from the dead to live in a "Pleistocene Park" in Siberia.

Restore & Revive, an organization that promotes "de-extinction," favors gene editing over cloning. The genes that differentiate an extinct species from a surviving one are identified, and switched into the living animal's genome.

Ben Novak, lead scientist at Restore & Revive, is working on inserting genes from the extinct passenger pigeon into the DNA of a band-tailed pigeon. 

"Hidden in the passenger pigeon genome are the key mutations to be able to take a bird today and engineer it to be what a passenger pigeon was," he told DW. "That's the idea — it is not about copying, it is about re-creation, a re-envisioning."

Elephants with funny hair

In the case of the mammoth, genes for the shaggy coat, small ears, subcutaneous fat and "antifreeze blood" that allowed it to thrive in sub-zero temperatures would be edited into the genome of an Asian elephant, its closest surviving relative.

Critics argue the resulting animal would not be a mammoth as such, but some kind of chimera that may or may not have much chance of surviving in the modern world. Or, as Britt Wray, author of Rise of the Necrofauna: The Science, Ethics and Risks of De-Extinction puts it, "an elephant with a bit of a funny haircut that can live up north."

Wray welcomed the news of northern white embryos as "fantastic," saying that alongside more traditional approaches to conservation, the new technology might "flip the script" for some species. But she's less enthusiastic about bringing back creatures from a world that no longer exists.

There are numerous technical challenges to overcome. Even with the complete genetic material of the recently extinct ibex, the short-lived infant was the only full-term pregnancy of 57 embryos implanted into surrogate mothers.

Wray points out that the cloned ibex's forerunner, Dolly the sheep, was the sole survivor of 277 attempted clones — and that was in surrogates of the same species. And even if the animal makes it, will it behave as its extinct ancestors did, with no living family to teach it?

"It's a whole lot of effort to cobble together a facsimile or a proxy of a majestic creature that we're all excited by," Wray told DW.

Resurrection scientists argue that extinct beasts wouldn't be brought back just for us to gawp at. While not true members of the extinct species, they could have the physical and behavioral characteristics to fulfill the ecological role of the original.

Restoring ancient ecosystems

When a species disappears, the whole ecosystem is thrown out of whack.

Aurochs — the primal cow of Eurasia — supported predator populations, for example, and their grazing helped other species such as plants and birds to thrive on the ground. Heck cattle — selectively "back bred" from domesticated cattle for their wild ancestor's characteristics — have been included in rewilding projects that aim to revive past biodiversity.

Even the mammoth, resurrection scientists argue, could help transform the the Siberian tundra into a grassland ecosystem as rich in biodiversity as the African savannah.

And that's not all. They even argue that by grazing vegetation and trampling winter snows, mammoths would expose the ground to colder temperatures and prevent permafrost from melting, slowing a dangerous climate change feedback loop.

Yet because there are so many variables at work in an ecosystem, Wray warns against hubris when it comes to recreating them based on our limited knowledge.

"Ecosystems are not just more complex than we currently think, they're more complex than we can think," she said. "It's not a plug-and-play scenario where you remove one variable, and then you add it back in and you're going to revert to how it was once was."

Resurrection science's detractors are perhaps most driven by the "moral hazard" argument: Trying to bring back lost species is a denial of the catastrophic finality of extinction, which might lull us into thinking we can turn back time even as a species dwindles away.

Let's not leave it so late next time

That's a concern for Cathy Dean, director of the United Kingdom-based charity Save the Rhino. 

She says while she wishes all the best to the team trying to coax life out of frozen northern white rhino material, her organization will focus on species that still have hope of surviving without such complex, costly, and uncertain conservation efforts.

"Unfortunately, the story for the northern white rhinos ended a decade ago when there were possibly six animals left in Granby National Park," Dean told DW. "You need 20 unrelated founder animals to have sufficient genetic diversity."

Today, Dean says, there are fewer than 80 Sumatran rhinos left, and just 67 Javanese rhinos — a situation although desperate, at least one where there is still enough genetic and demographic diversity to give them a real shot at survival.

But unlike Sudan, the last male northern white who died in May, we don't know the Sumatran or Javanese rhinos' names, and they aren't making headlines across international media with online dating profiles or cutting-edge gene technology.

"I think this is really lesson for all of us that you should not allow a situation to get quite so desperate," Dean said. "And the heartbreaker with the northern whites is that there were opportunities, there were two really good chances in the mid-90s and then again in 2005, which for political reasons weren't taken advantage of."