If I asked you to describe a leopard, I'm almost 100% certain you'd tell me about a large golden cat with black spots all over its body. It's a truly iconic image. Maybe if you'd read the leopard characteristics page you'd be able to tell me that the colour of the coat and the pattern of the spots actually varies throughout the different leopard habitats. But maybe you wouldn't know about the plain black leopards that can be found in some corners of this world. So distinctive are these black leopards that indigenous people traditionally thought they were a different species. These entirely black leopards are most commonly known as black panthers. Since the 1960s it has been considered by some to be politically incorrect to call any black big cat a black panther, due to links with political parties, criminals, military units etc. In technical terms, the black form of any big cat is known as a melanistic form.
Black Panther is, confusingly, the common name for both melanistic leopards and melanistic jaguars. Differentiation is surprisingly easy – jaguars are only found in the wild in the Americas, and leopards are never found in the wild in the Americas. So a large black cat observed anywhere in the wild outside the Americas is a melanistic leopard, and a large black cat observed inside the Americas is a jaguar.
In leopards, the black appearance is caused by a recessive allele. Alleles are different forms of a gene – so for example in humans, the gene for eye colour has a blue allele and a brown allele. Because the allele for all black fur is a recessive allele in leopards, for a leopard to have black fur all over its body it has to inherit the gene from both parents. Spotted leopards can produce black cubs, because both of the parents can carry the gene without displaying it – the allele for spotted fur is dominant over the allele for black fur. If two black leopards mate, they will always produce black cubs. If one black and one spotted leopard mate, then black cubs only have a chance of occurring if the spotted leopard carries the allele for black fur silently.
Although melanistic leopards appear to be completely black with no rosettes, close inspection reveals the markings are still there, they're just well hidden because the rest of the fur is also black. The faint patterning is known as "ghost striping".
Black leopards are commonly found in dense forests in South west China, Burma, Assam and Southern India. They are relatively common in Java, so common in fact that some counts estimate they are more melanistic leopards than spotted leopards. In Malaysia, the local people, the Orang Asli, were unable to recognise a spotted leopard; they were only familiar with the melanistic form. Although melanistic leopards are less common in Africa, they have been seen in Ethiopia, the forests of Mount Kenya and the Aberdares. Being melanistic in areas like these is thought to be advantageous, because light levels are lower so it easier for dark leopards to blend in. This may explain why melanistic leopards are more common in these areas.
However, there are other theories that may explain why melanistic leopards are common in some areas, theories more complicated than camouflage. These theories are particular pertinent to the Malaysian leopards, where black fur is the norm. Being able to hide is incredibly important to a leopard's survival. But so are other things, such as being able to fight off disease. Scientists have uncovered a link between the colour of fur and the effectiveness of the immune system (the processes in every living body that stop it from getting ill). So it may be that during an outbreak of disease at some point in the past, the black fur arose as a response to disease. Or it may be that the simpler camouflage theory is right. We don't know. The only thing we really know with some certainty is that the leopards that first arrived in Malaysia about 150,000 years ago will have been spotted, just like the original African cats. Then over time the black fur will have developed and eventually become more common. But the truth behind the melanistic leopards is as mysterious as the leopards themselves.
As humans, we are insatiably curious about these mysterious melanistic creatures, and so they are one of the most common forms of big black cat in captivity. The black cats in captivity are more temperamental than their spotted equivalents, and mothers more frequently reject their cubs. Although it has been claimed that this is because of their black colour, in actuality it is a response to inbreeding. In an attempt to ensure cubs with black fur were born, in the past zoos bred close family member together, which has resulted in poor temperament, and an increased likelihood of mothers rejecting their cubs. Litters also tend to be smaller, implying the captive melanistic leopards are less fertile.
One captive melanistic leopard that moved from Dublin Zoo in Ireland to Glasgow Zoo in Scotland before ending up Madrid Zoo in Spain really stood out from the crowd. Although she had the black coat synonymous with being a melanistic leopard, she had a sprinkling of white hairs all over her body. People compared it to cobwebs, and she was given the nickname the Cobweb Panther. It is thought the white hairs were caused by vitiligo, a condition humans suffer from too when they get white patches on their skin. Since her condition was noticed in the 1980s, more Cobweb Panthers have been noticed in zoos across the world.