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Sudan, the last male northern white rhino, has died. Museum mammal curator Richard Sabin explains what this means for the evolution of the species.
The death of Sudan, who lived in the Ol Pejeta Conservancy in Kenya, means there are just two northern white rhinos left, both females. It leaves the subspecies with little hope of escaping extinction.
Sudan was 45 years old, and suffering from a degenerative disease that caused skin wounds as well as changes in his muscles and bones.
After his condition worsened and left him unable to stand, vets decided to euthanize him. It means the subspecies is clinging to existence by a thread.
Richard Sabin, a mammal expert at the Museum, says, 'It's unfortunate that we are facing the loss of this subspecies and the opportunities to objectively study the significance of its role in the evolution of the rhinoceros.'
It is with great sadness that Ol Pejeta Conservancy and the Dvůr Králové Zoo announce that Sudan, the world’s last male northern white rhino, age 45, died at Ol Pejeta Conservancy in Kenya on March 19th, 2018 (yesterday). #SudanForever #TheLoneBachelorGone #Only2Left pic.twitter.com/1ncvmjZTy1— Ol Pejeta (@OlPejeta) March 20, 2018
Sudan's death is a terrible tragedy. But to understand its real significance it is necessary to examine rhinos' evolutionary history.
The earliest members of the rhinoceros family appeared in the fossil record about 50 million years ago, comparatively recently in geological terms. Over time, rhinoceroses became a very diverse group, growing to huge sizes and living in a variety of environments.
Richard says, 'Nowadays, people think of rhinos living in hot countries. But it wasn't always this way. For example, woolly rhinos - as their name suggests - had thick, woolly coats and became adapted to life in much colder, drier climates.
'Now we have just five living rhino species left, a poor remnant of their former diversity.'
The five surviving species of rhino are the white and the black rhinos in Africa, and the greater one-horned, the Sumatran and the Javan rhinos in Asia.
Sudan was a northern white rhino, a subspecies of the white rhino.
Other rhinoceros species died out over millions of years, mostly because of changing climates and environments. But human activity is having the greatest impact on the final few species.
For instance, the poaching crisis of the 1970s and 80s wiped out the northern white rhino populations in Uganda, Central African Republic, Sudan and Chad. It was fuelled by demand for rhinoceros horn for use in traditional medicines in Asia and ceremonial dagger handles in Yemen.
The last remaining wild population of northern white rhinos, made up of between 20 and 30 individuals in Garamba National Park in the Democratic Republic of the Congo, were killed during fighting in the region in the 1990s and early 2000s. By 2008, the northern white rhino was considered by most experts to be extinct in the wild.
Sudan arrived at Dvůr Králové Zoo in the Czech Republic in the 1970s. In 2009, he was moved to Kenya with one other male and two females.
The other male was called Suni, and died of natural causes in October 2014.
Sudan's genetic material has been collected and could be used for future attempts at preserving northern white rhino genetic diversity.
However, there are only two female northern white rhinos left on the planet – Sudan's daughter Najin and her daughter Fatu, who remain at Ol Pejeta. The only hope for the preservation of this subspecies now lies in developing in vitro fertilisation (IVF) techniques using eggs from the two remaining females, stored northern white rhino semen from males and surrogate southern white rhino females.
This has never been done with rhinos before and comes with risks. The estimated cost of the procedure, from the development of the method, to trials, implantation and the creation of a viable breeding herd of northern whites – could be as much as £6.5 million.
According to Richard, it may not be the best way to preserve the genes of this subspecies.
The southern and the northern are two subspecies of the white rhino.
While the northern faces extinction after Sudan's death, the situation for the southern is less dire. There are nearly 20,000 of them - their populations are increasing and they are classified as Near Threatened by the International Union for Conservation of Nature (IUCN). Without careful management and protection, however, they could also be at risk.
The IVF programme could produce viable offspring, but the available northern white rhino gene pool is so limited there could be problems caused by inbreeding, which may compromise the success of the whole programme. It's also highly unlikely that scientists would ever be able to recreate a northern white rhino using the genetic material that remains.
Richard says, 'If the IVF programme fails and the northern white rhinos become completely extinct, their hugely important adaptive genes are lost forever.
'That would be a tragedy because it will impact how the white rhino continues to evolve in years to come.
'The northern white rhino's classification as a subspecies relates to how they have evolved and adapted in different ways to the other white rhinos. These genetic and physical adaptations to changes in the environment over time have led to the development of adaptive genes.
'The worry now is that we may not be able to halt the loss of genetic diversity that we are seeing in rhinoceros populations, or adequately preserve significant genetic material.
'Conservationists need to find the best way of doing that, to give the species as a whole the best chance of survival in the future. If you lose genetic diversity, it becomes harder for a species to keep evolving, adapting and ultimately surviving.'
It's not the first time that a species has been lost before scientists really got the chance to understand the significance of their position within their ecosystem. The Tasmanian tiger (thylacine) and quagga (a form of zebra) suffered the same fate.
There are threats facing other large mammal species. Habitat loss is the greatest threat globally, followed by illegal hunting.
Richard says, 'Being a large mammal in the wild can be a problem. Unless they live in remote places, far from human activity, they struggle when they encounter expanding human populations.
'There are things we can all do to help protect animals in the wild. We can be aware of how we are affecting the environment, especially when we go on holiday. We can think about our carbon footprint and the impact we have on other resources.
'Ethical, green tourism is so important. For example, always go on safari with an approved, accredited company, in a way that won't put unnecessary stress on animal populations. Don't unwittingly fuel the trade in endangered species by purchasing souvenirs which may be made from material taken from illegally hunted animals.
'You can also get involved wherever you are in the world. Be vocal, express your views, petition governments to do more, and support internationally recognised conservation organisations.'