There may only be two northern white rhinos left alive, but scientists say there is hope yet to bring the 'doomed' beasts back from the brink of extinction.

Experts had worried that resurrecting the subspecies using frozen cells could create a heavily inbred population.

New research shows the species has enough diversity in its DNA to survive this 'genetic bottleneck'.

During such a bottleneck only a small number of animals contribute to the gene pool leading to a weaker species that struggles against disease outbreaks and environmental changes.

The closely-related southern white rhino recovered from a similar position following a sharp drop in numbers driven by poaching and habitat destruction.

In the early 20th century the subspecies was world's most endangered rhino with just 20 left alive, but there are now more than 20,000 in the wild.

Scientists said the northern white could make a similar recovery through conservation efforts that make use of frozen cell lines.

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There may only be two northern white rhinos (pictured) left alive, but scientists say there is hope yet to bring the 'doomed' mammals back from the brink of extinction

Lead author of the study Tate Tunstall, of the San Diego Zoo Institute for Conservation Research, said: 'The southern white rhino went through a severe genetic bottleneck, but is now the most populous of all forms of rhino at ~20,000 individuals, suggesting that a genetic rescue utilizing these cell lines could be the foundation for a similar recovery in the northern white rhino.'

The world's last male northern white rhino, Sudan, died in Kenya at the age of 45 in March, survived by just two females - his daughter Najin and granddaughter Fatu.

Without a male to breed with, scientists had hoped to use a small stock of frozen sperm to perform rhino IVF on Sudan's surviving kin and save the species.

In vitro fertilization is used in the cattle industry to breed more robust herds, and a Cape buffalo was conceived through IVF for the first time in 2016.

Because Najin and Fatu are two weak to carry a pregnancy to term meaning scientists would implant the resulting embryo in a southern white.

Because the females are related scientists had worried the resulting population could end up heavily inbred.

The world's last male northern white rhino, Sudan, died in Kenya at the age of 45 in March. Scientists had worried that resurrecting the subspecies using frozen cells could create a genetic bottleneck that would lead to a heavily inbred population

SCIENTISTS PIN HOPES ON IVF TO SAVE THE NORTHERN WHITE RHINO FROM EXTINCTION While the death of Sudan marks a symbolic turning point in the fight to save the northern white rhino, in fact the survival of the species has been entirely reliant on untested IVF techniques for years. It was hoped that Sudan, his daughter Najin and granddaughter Patu might be able to produce offspring when they were moved to Kenya in 2009, but their close genetic relationship rendered them infertile. Since at least 2015 scientists have been working with IVF and stem cell techniques in the hopes of being able to create a viable northern white rhino embryo, according to a GoFundMe page for the project. Researchers in Berlin and San Diego are using DNA samples collected from a dozen northern whites, including Sudan, and trying to apply techniques developed for humans to the animal. If a viable embryo can be created, it would then have to be implanted into the womb of a southern white rhino, since Majin and Patu will likely be dead before the technique is perfected. While the southern white rhino would be responsible for giving birth to the baby, because the infant's genetic material came solely from northern whites, it would be a member of that species. However, as Save The Rhino points out, the process is fraught with difficulty and has a low chance of success. In the last 15 years just 10 rhino births have resulted from artificial insemination and only two embryos have ever been created - one of which divided into two cells before perishing, and the other one into three. For the northern white rhino to be genetically viable a minimum of 20 healthy individuals must be born - meaning the whole process must be successfully completed 20 times - to avoid inbreeding. Then, it would be necessary to find a suitable habitat for them, since their old habitat has largely been destroyed and led the species to the brink of extinction in the first place. Advertisement

Scientists could coax nine frozen cell lines, saved from dead rhinos, to become egg and sperm cells for IVF treatments but even this would leave little genetic diversity.

In the new study, researchers investigated whether the northern white could recover using frozen cells stored at San Diego Zoo.

Scientists sequenced the full genome of these cell lines, which represent eight unrelated northern whites, and compared them to the genomes of southern whites.

They confirmed the long-standing theory that the two rhinos are subspecies rather than distinct species.

Sudan was survived by just two females - his daughter Najin (left) and granddaughter Fatu (right). Without a male to breed with, scientists had hoped to use a small stock of frozen sperm to perform rhino IVF on Sudan's surviving kin and save the species

This is good news if researchers are to use a southern white to carry an IVF implanted northern white to term in future, as doing so through a separate rhino species would be less likely to succeed.

The scientists also found healthy genetic diversity in their northern white samples when compared with the southern white rhinos.

This means the Sandiego Zoo samples may serve valuable pools of genetic material for a future rescue of the species - either by coaxing them into sex cells for use in IVF or other methods, such as cloning.

'If it came down to the materials in the Frozen Zoo, we could turn those cells into animals,' study coauthor Dr Oliver Ryder told the New York Times.

The study also showed that the southern white rhino now has a healthy genetic diversity despite once finding itself close to extinction.

New research shows the closely-related southern white rhino (file photo) recovered from a severe genetic bottleneck following a sharp drop in numbers driven by poaching and habitat destruction

Semen from dead northern white rhinos is stored in various locations around the world, and the result provides hope for those looking to resurrect the northern white.

Supporters think the work could be used to help other endangered species, while some conservationists believe the focus should be on other critically endangered species, including the Javan and Sumatran rhinos, that have suffered because of poaching and human encroachment on habitats.

Northern white rhinos were particularly vulnerable because of conflicts that swept their central African range.

The last ones in the wild were observed more than a decade ago in Congo's Garamba National Park, a frequent target of well-armed poachers.

In the new study, researchers investigated whether the northern white could recover using frozen cells stored at San Diego Zoo. Pictured is Sudan, the world's last male northern white, shortly before he died in March

The 'much-hyped' plan for rhino in vitro fertilization is probably too late to save the northern white subspecies, according to Save the Rhino, a London-based group.

'With small chance of healthy new calves, and limited place in their historic range to go, Save the Rhino believes that the best outcome will be to put our efforts and funding - including research into IVF - into saving the species which do still have a chance,' it said on its website.

'The real fight for the survival of northern white rhinos in their natural habitat was lost over a decade ago,' Jo Shaw, African rhino expert with the WWF conservation group, told the Associated Press in March.

'Large mammals, like rhinos, should be seen as symbols of large functioning ecosystems and we must focus our efforts and energy on their protection and ongoing survival within these vital landscapes around the globe.'