Sudan was unable to stand up in the end. He was treated for age-related complications that led to degenerative changes in muscles and bones combined with extensive skin wounds. Veterinary experts took the decision to euthanize the animal." At the age of 45, Sudan was a very old man, well over 100 years old in human equivalent years," said the charity Helping Rhinos.

Rhino horns are used in traditional Chinese medicine and for dagger handles in Yemen. A poaching crisis in the 1970s and 1980s wiped out northern white rhino populations in Uganda, the Central African Republic, Sudan and Chad. The last wild population was in the Democratic Republic of Congo, but that succumbed to fighting in the region. At Ol Pejeta, Sudan was constantly under armed guard.

Given the danger that Sudan he would have been in when so much younger, he was among a group of northern white rhinos who were taken to a safari park in Czechoslovakia in the 1970s.

Sudan and a group of other northern white rhinos were moved back to Africa in 2009 in the hope that the move, in particular grassland at the Ol Peteja Conservancy in eastern Kenya, would give them more favorable breeding conditions.

The death of the only other northern white male, Suni, of natural causes in October 2014, further emphasized the need to urgently come up with alternative solutions for breeding.

Sudan eventually lived at Ol Peteja with the only other two members of his subspecies — his daughter Najin, and his granddaughter Fatu. Because of myriad health complications that mean the two cannot bear offspring, any future northern white rhino would have to be carried in pregnancy by southern white rhino female surrogates. However, their eggs would be used.

Often hybrid animals are purposefully bred. But due also to forces of nature, animals migrate further than before, mating with other species already in the region. This is making for some weird and wonderful crossbreeds.

One such animal that is now being found in nature is the grolar bear - the product of, you guessed it, grizzly and polar bears. Melting ice caps have seen polar bears moving south, while the warmer climate means grizzly bears are migrating north. This means that larger areas of their territories are overlapping, giving them more chance to crossbreed.

Scientists have called natural crossbreeding between different types of blacktip shark off the coast of Australia "evolution in action." For some hybrid species, like the offspring of common blacktip and Australian blacktip sharks, this means the best of both genepools - such as being able to cope in both tropical as well as cooler waters.

But it’s not all positive. There is the fear that crossbreeding will lead to the extinction of animals like the polar bear. As the population decreases, the likelihood that polar bears will mate instead with grizzly bears increases as does the probability that polar bears could eventually disappear.

Many hybrids suffer from genetic abnormalities, are more prone to disease and are often infertile. One such animal is the liger. A cross between a male lion and a tigress, this produces a creature that Big Cat Rescue calls a result of "irresponsible breeders" looking to make money. This animal does not occur naturally in the wild.

Breeding hybrids in zoos is frowned upon. But on farms, It's hard to stop nature. Rarely, there have been cases where sheep and goats have found each other and decided to … well, you know. The result is a geep, like this one born in Ireland.

Regardless of the positives or negatives of hybrids, some animals will even go out of their way to consummate their interspecies love. Back in 2013, a male zebra jumped over the fence of his enclosure to mate with a female donkey in Florence, Italy. The result was this cute little zonkey called Ippo.