Scientists are therefore exploring a second frontier: stem-cell technology.
Frozen tissue samples from northern white rhinos are preserved in biobanks.
Researchers hope that cells from these tissues could eventually be transformed into induced pluripotent stem cells and then into reproductive cells such as sperm or eggs.
BioRescue says preserved tissue could potentially expand the usable genetic pool beyond the small number of individuals represented by today's natural eggs and stored sperm.
This approach remains experimental.
But it highlights how extraordinary the situation has become.
Conservation once meant protecting habitat and stopping hunters.
Those goals are still essential.
But for the northern white rhino, conservation now also involves cryogenic storage, laboratory fertilization, stem cells, surrogate pregnancy and reproductive medicine.
Scientists are effectively attempting to rebuild a population after conventional conservation arrived too late.
The Photograph Became Bigger Than Sudan
All of that science began attracting much wider public attention after Sudan's death.
And one photograph helped transform an abstract conservation crisis into something emotionally understandable.
In Ami Vitale's image, the idea of extinction is reduced to a relationship between two living beings.
A keeper bends toward an elderly rhino.
The animal is dying.
The person beside him knows there will never be another male northern white rhino walking the Earth after Sudan is gone.
It is difficult to imagine a clearer visual representation of loss.
National Geographic later identified the image as one of the photographs that had generated especially strong responses from its audience.
Vitale herself has said that documenting Sudan changed the direction of her work.
Earlier in her career she photographed human conflict in places such as Kosovo, Afghanistan and Gaza.
Over time she became increasingly interested in the relationship between humans and the natural world.
Sudan became central to that shift.
His story demonstrated that wildlife conservation is not separate from the human story.
Humans contributed heavily to the northern white rhino's collapse.
Humans also protected the final survivors.
Humans guarded Sudan day and night.
Humans created embryos in laboratories.
And ultimately humans were there beside him when he died.
More Than Poaching
It is tempting to reduce the northern white rhino's disappearance to a single cause.
In reality, its collapse reflects several interconnected problems.
Poaching was devastating.
But armed conflict and political instability in the rhino's historic range also weakened protection efforts.
Conservation authorities cannot easily protect animals when wildlife reserves exist inside regions affected by violence.
Small populations then become even more vulnerable.
Once numbers fall low enough, reproduction itself becomes difficult.
Animals may struggle to find mates.
Genetic diversity declines.
Older individuals die faster than new animals are born.
At that stage, preventing the death of individual animals may no longer be enough to recover the population.
The northern white rhino crossed that threshold.
By the time Sudan became internationally famous, the crisis had been developing for decades.
His fame did not come because conservation had succeeded.
It came because almost everything else had already been lost.
A Warning for Other Species
That may be Sudan's most important legacy.
Waiting until a population reaches two or three animals is extraordinarily dangerous.
Advanced reproductive technology can create possibilities, but it is expensive, technically difficult and uncertain.
Even scientists involved in the northern white rhino project emphasize that technology should not become an excuse to neglect traditional conservation.
Protecting species while viable populations still exist is far easier than attempting to reconstruct them after they have effectively disappeared.
Habitat protection matters.
Anti-poaching enforcement matters.
Reducing illegal wildlife trade matters.