In the past, little was known of genetics or of the limitations on hybridization. It was well known that lions and tigers in menageries could produce hybrid offspring and that dogs and wolves could produce offspring. Horses, asses and zebra can all produce offspring in any combination. In all cases the parents were closely related and similarly sized. Wolves and dogs are so closely related that the offspring are fertile. Ligers and tigons are closely enough related that the offspring are partially fertile i.e. the female is often fertile but the male is rarely fertile. The wide variety of horse/ass/zebra hybrids are rarely fertile excepting a few reported occurrences of fertile female mules.

Early explorers and biologists believed in hybrids purely on the basis of an animals appearance. For example it was believed that lions and panthers ("pards") would mate to produce leopards, that the giraffe was a fantastical mix of camel and leopard (hence its original name "cameleopard") and that cats and rabbits would mate to produce cabbits. While lions and leopards can produce offspring (leopons), the cameleopard is impossible as the supposed parent species are only distantly related and the cabbit is actually a Manx cat (a tailless mutation).

Many sightings of anomalous British big cats are reported by members of the public who are enthusiastic rather than expert and who have limited understanding of hybridization. Their varying descriptions or fuzzy photos and films may be interpreted and identified by those who did not see the animal first. In this game of Chinese whispers, many big cats are reported as hybrids of some sort. Are these cats being poorly identified leading to the number of hybrid ABCs being vastly over-reported? What we do know of big cat hybridization would suggest so.

As far as possible I've avoided technical terms, however the following definitions (grossly simplified) will be useful to the reader.

Inter-specific: hybrids between two different species e.g. between lion and tiger.

Intra-specific: hybrids between two sub-species of the same species e.g. between Siberian tiger and Bengal tiger.

Sub-species: a geographically localised population with distinct characteristics which differentiate it from a population localised elsewhere e.g. the different mane colours/densities of lion subspecies

Breed: a variety within a species, produced or refined by human selection to fix certain traits, as opposed to a geographically localised sub-species population formed by natural selection. E.g. Siamese cat and Persian cat.

Hybrid: an individual whose parents are from different species or different subspecies or different breeds (depending on context).

Pure-bred: an individual whose parents are both the same species i.e. not a hybrid.

Back-cross: to mate an offspring back to a purebred individual (usually to one of its own parents).

Inbreeding: breeding together very closely related individuals e.g. brother/sister, mother/son, father/daughter.

Taxonomy: means of grouping organisms into related groups based on similarities/differences of form and DNA.

Big cats will range widely in search of prey and if enough males and females of one species were let loose in a single area, a viable population could arise. If there are too few individuals of the same species then the gene pool is limited and inbreeding depression occurs. Inbreeding depression results in poor fertility, greater susceptibility to disease and can cause entire populations to die out. With only a few individuals present in one area there is an increased risk that an all-male or all-female population will occur, leading to a dead end.

In captive situations, the drive to breed may be so strong that big cats of different species will mate with each other if no mates of their own species are available. This recently happened (2000) in a Chinese circus when a lioness accepted a tiger as her mate and produced several stillborn offspring. It is believed to have happened in exceptional circumstances the wild between solitary lionesses and male leopards, despite the leopard being smaller than the lioness. Britain may be such an exceptional circumstance, driving individuals of two different species to mate with each other due to a lack of more appropriate partners.

Britain is not the only area where hybrid big cats are believed to prosper. According to crypto-zoologist Karl Shuker, parts of Africa (particularly more isolated mountainous areas) have long-standing traditions of spotted lions which local people believe to be naturally occurring leopard/lion hybrids. The spotted cats have tawny markings on a pale background colour and are called "marozi" in Kenya (as opposed to "simba", the word for lion). In Uganda they are "ntararago". In Ethiopia they are "abasambo" while in Rwanda they are "ikimizi".

Descriptions of African spotted lions vary from area to area, but in general they are reported to be intermediate in size between lions and leopards and to live and hunt in pairs or packs. This is not in itself evidence of a hybrid identity since the "packs" and pairs might be coalitions of young males expelled from their natal pride and could include both maned and maneless males. Their lesser size and tawny markings may well be due to them not having reached their full growth. Alternatively, the spotting might be the result of inbreeding among an isolated population fixing a mutation which causes juvenile markings to persist into adulthood.

Parts of India also have a tradition of hybrids such as the leopard/tiger hybrids known as the "dogla". Doglas are the result of large male leopards mating with tigresses. Early 20th Century attempts to produce a comparable hybrid known as a "tigard" in captivity resulted in the offspring being miscarried at a relatively early stage. The pattern would be a combination of stripes and rosettes, most likely a marbled or swirled appearance with stripes on the legs and tail if the domestic Bengal (striped tabby mixed with rosetted wild cat) is used for comparison.

In Central America there are believed to be hybrids between the puma and the jaguar and a creature resembling such a hybrid has been shot. In captivity, puma and leopards have been successfully cross-bred. Both are reported to have tawny markings on a sandy background.

To date, all reports of leopard/lion, leopard/tiger or jaguar/puma hybrids in the wild have been based on appearance and on local myth. Although local people in those regions of Africa and India are highly knowledgeable about local animal species, the myths and beliefs are based on visual impressions and are not always correct. For example the supposed leopard/cheetah hybrid turned out to be pattern mutation in the cheetah (king cheetah). In Britain, people are far less familiar with big species, seeing them on TV or in zoos and circuses or on occasional safaris, and far more likely to mistake the identities of what they see.

Several big cat species are inter-fertile i.e. they can breed with each other and produce viable hybrid offspring. However, the offspring may be infertile. Male hybrids are almost always sterile - although they display mating behaviour, they cannot fertilise a female (either a hybrid female or a pure-bred female). Female hybrids are often fertile, but because male hybrids are sterile, the female hybrids must mate with pure-bred big cats and these matings are not guaranteed to produce offspring.

Again, a comparable situation occurs in domestic Bengal cats. The original domestic x Asian Leopard Cat hybrids result in fertile females and infertile males or males which are reportedly fertile for a limited period of time. In the Safari breed (domestic x Geoffroy's Cat hybrids) the first generation males are reportedly fertile. Dissection of zoo-bred big cat hybrids indicates that the males are sterile although the unpredictability of gene interactions means there may possibly be occasional partially fertile males (the likelihood is remote but such oddities should never be ruled out entirely).

The offspring of a pure-bred individual of one species mated with a pure-bred individual of another species are known as first generation hybrids. There are genetic and practical limitations on inter-fertility.

Leopards and lionesses can produce leopons but the reverse mating (lion with leopardess to produce lipards) appears unsuccessful because the smaller leopardess cannot carry the lion's large offspring to full term. Leopards and pumas have produced offspring (pumapards), but the offspring suffered dwarfism and died young. Tigers and leopardesses produced stillborn offspring (tigards). 

It must be said that more ligers, tigons and leopons have been bred because of their popularity as exhibits while there have been too few attempts at breeding the other combinations mentioned to know whether the dwarfism and stillbirths were due to the particular individuals used in the mating or are a general rule for that mating combination. One thing that is known and has been tested in other mammals is that a mismatch or conflict between the maternal genes and paternal genes can cause growth dysplasia (growth problems) in the foetus leading to undersized offspring, oversized offspring, placental abnormalities or spontaneous abortion.

Jaguar x lioness hybrid (jaglion). This is a taxidermised individual on display at the Rothschild Zoological Museum in Tring, England.

Assuming that live offspring are produced and survive to breeding age, second generation hybrids may be produced by back-crossing a female hybrid to a pure bred of the same species as one of her parents e.g. a tigon female to a tiger (ti-tigons) or to a lion (li-tigons), a liger female to a lion (li-ligers) or to a tiger (ti-ligers). These will be three-quarter breds containing 75% genes from one species and 25% from the other.

Hybrid to hybrid matings have so far been unsuccessful due to male sterility. There has been one unconfirmed report of lion/tiger hybrids mating to produce offspring and hybrid males have been seen to mate with females. Since cats can produce litters where each cub has a different father, it is far more likely (in my opinion) that the hybrid male was not the father and that a pure-bred lion or tiger in the same enclosure also mated with the female and that he fathered the cubs.

Currently there are no reports as to whether the second generation hybrids are fertile but in a comparable situation in domestic cats (the Bengal, the Safari), the second generation males and females are both fertile.

Complex hybrids have been created by crossing a female hybrid to a big cat of a different species e.g. a male jaguar-leopard (jagleop) to a lion to produce a lijagleop. This results in 50% lion genes, 25% jaguar genes and 25% leopard genes. Although no-one has continued the experiment, complex hybrid males will almost certainly be sterile. It is probable (but not confirmed) that the females will also be sterile due to mismatches between the complex mix of 3 sets of genes.

In domestic cats (the Viverral breed) the original Bengal hybrid was stabilised over several generations of back-crossing to domestic cats (greatly diluting the Asian Leopard Cat genes so that the Bengal is considered a wholly domestic breed with normal fertility) before genes from another wild species (the Fishing Cat) were introduced and a whole new hybrid created. It will take multiple generations of back-crossing to stabilise the new breed.

Note: The situation with domestic cats breeding freely with African Wild Cats and European Wild Cats is not comparable as these are taxonomically sub-species, not separate species. This would be comparable to breeding Siberian tigers to Bengal tigers i.e. intra-specific hybrids.

There have been reports of puma/leopard hybrids in the wild in Britain and of such a hybrid being seen in the company of a lynx. The viability of such a pairing depends on which is the male, but even if they did produce complex hybrid offspring, the lynx-pumapards are unlikely to be fertile themselves and the family line would come to an end. Lynx have been hybridized with the related bobcat, but not with other big cats nor with domestic cats.

Introgressive hybridization is the formation of a new species due to the continued reproduction between fertile individuals of different sub-species or members of related species. The individuals and their offspring breed among themselves for long enough that distinct traits become fixed. This has probably happened in Britain to create the Kellas Cat, a black wildcat intermediate in form between the Scottish Wildcat and black domestic cats Scottish Wildcats and domestic cats are closely related sub-species and have fully fertile hybrid offspring. Black is a recessive trait (two black cats will produce black offspring) and can remain hidden in a population i.e. two tabby cats can have black kittens. If the black hybrids mate only with other black hybrids, they will produce a population of cats which may vary in size and shape but which will always be black.

The "Rabbit-headed Wild Cat", another black wild cat, may well be an introgressive hybrid between wildcats and a black domestic cat containing a high degree of Siamese ancestry. It has the wide-set large ears, wedge-shaped profile and slightly protruding canines found in Siamese and Oriental cats. Two such cats are reportedly in captivity, but have failed to breed. This has been explained as due to their hybrid nature. However, hybrids between the Scottish Wildcat and domestic cat are fully fertile to the extent that many Scottish Wildcats are "mongrels". The failure to reproduce is more likely due to inbreeding depression i.e. the pair are so closely related and genetically similar (e.g. brother/sister) that their fertility is poor. This effect is seen in wild cheetahs and in laboratory mice. To test for infertility, both captive black cats should be test-mated to Scottish wildcats and also to domestic cats rather than to each other.

Introgressive hybridization between different big cats is theoretically possible e.g. if a male leopard mates with a lioness, then with his leopon hybrid female offspring and with her hybrid leo-leopon female offspring and so on. If the Bengal cat example is typical, consistently fertile males would start to occur in the second or third generation, though the lion genes would be greatly diluted by that stage. Because the leopard would mate with several different generations of hybrid females with different ratios and combinations of lion and leopard genes, there would be a variety of genetic mixes. There would also be inter-generational matings producing offspring e.g. leo-leo-leopon male with first generation leopon female, leopard male with leo-leo-leopon female. Eventually a true-breeding population would form. The cats would be closest in appearance to (possibly indistinguishable from) the leopard, since he will have contributed most of the genes in the eventual mix. In domestic/wild hybrid breeds the eventual percentage of wild-type genes is reckoned to be about 12.5% (although I do not have the formulae demonstrating this).

If the marozi does indeed exist and is not simply an aberrant form of lion, it may be an introgressive hybrid where the lion has contributed most of the genes and all that is left of the leopard's contribution to the gene pool is the rosetted pattern (but in lion colours) and smaller size.

To produce a viable hybrid big cat population in Britain would require continued back-crossing of hybrid females to a pure-bred male of the same species as either parent (most likely to her own father) until fertile males are produced in a later generation. By the time fully fertile generations occur, they would so greatly resemble the pure bred foundation male and the genes from the other species would be so dilute that only a DNA analysis would reveal any trace of the other species!

This is already seen in domestic cats. The Bengal breed is so many generations removed from the Asian Leopard Cat parent that a casual observer would see only a "tabby cat" or "spotted tabby cat". A non-expert would not know that Bengals have any wild genes at all. Only someone familiar with pure-breds would spot the distinguishing markings and face shape. The few first and second generation Bengal hybrids, which more greatly resemble the Asian Leopard Cat, remain with Bengal as foundation stock. If the Bengal can be misidentified as "not a hybrid" then pure-breds can be misidentified as hybrids and pure-breds with natural colour or pattern variations are even more likely to be misidentified as hybrids (as happened with the king cheetah).

However enthusiastic they are, most people in Britain are not experts in big cat identification. A few visits to a zoo or circus, a spotter's guide to African wildlife and a few hours in front of Discovery Animal Planet do not make somebody an expert! Those who do see ABCs usually catch only a fleeting glimpse or see them at a distance; very few see them close up. Even an expert is hard pressed to make a positive identification of a fast-moving big cat at the other end of a field at dusk. Big cats are also variable in size and markings. Lion cubs and puma cubs have rosette markings and some adults retain these as faint markings. Claims of "puma-leopard hybrids" should therefore be treated with scepticism, not confidence, as they are far more likely to be sub-adults with residual markings.

While there are genuine sightings, to date all big cat captures have been pure-breds - a puma in Scotland, a lynx near to London and an escaped clouded leopard. There have been a far greater number of misidentifications. Some of these inexpert identifications (which make excellent tabloid newspaper headlines) have caused "flaps" (groups of sightings).

To demonstrate how inexpert some people are, here are two of the most ludicrous misidentifications. A "lion" on a railway bank turned out to be a large ginger moggy viewed from a passing train. And to demonstrate just how little many people know about cats, in America, a woman reported a "lynx" sitting on her fence; this turned out to be her neighbour's Siamese cat - a popular and very distinctive breed! If people can mistake a relatively small domestic cat for a big cat, then they are even more likely to mistake a juvenile puma with faint markings as a "hybrid leopard-puma"!

A NEW SPECIES?

Some, for example the X-project, erroneously claim that the Exmoor Beast is a "prime example of micro-evolution", being descended from an escaped black puma that mated with a leopard and created a new species of cat. The small and isolated gene pool, the rare black colouration of the puma became a "common" trait while the adaptability of pumas supposedly enabled the new species to fit a non-native environment.

This is nonsense for several reasons. Melanism has not yet been confirmed in pumas. A single dark puma was shot in South America, but it was not melanistic and more recently a litter of charcoal puma cubs was found, but it is not known if these will retain that colouration. The "rare black colouration of the puma" remains anecdotal. While a leopard has been crossed with a puma in captivity, the offspring were dwarfed and short-lived. In addition, male hybrids are almost invariably sterile while female hybrids are only fertile if bred back to a pure-bred male of one of the parent species. This "backcrossing" would lead to later generations being more absorbed back into one of the parent species (a good example is the Bengal cat created by crossing Asian Leopard Cats with domestic cats - backcrossing to domestics has resulted in a wholly domestic conformation). The identification of the beasts as black pumas is due to poor light/silhouette and the fact that the British public are not familiar enough with big cats to distinguish between puma, leopard, jaguar or lioness (a trip to a zoo or an Africa safari does not qualify a person to identify a big cat!).

A CANINE NOT A FELINE?

Most British Big Cat "evidence" is in the form of paw-prints and kills. These have been shown to tracking and trapping experts with experience of big cats in the wild in other countries. These experts are people whose livelihoods depend on them being able to identify big cat signs and track and even trap or shoot big cats. They identified almost all of the paw-prints as dog, with the remainder being too indistinct for identification. In the cases of supposed ABC sheep kills, those big cat experts noted that the pattern is consistent with dogs - lacerations to the neck and belly with the skin being removed from the neck and with the belly area being eaten. Dog packs tend to kill by evisceration. Big cats go for the throat or neck and leave four deep puncture wonds. Either the neck is broken or the prey is strangled. Big cats do not leave gashes in the throat. Dogs kill more messily and leave gashes. It would seem that most of these livestock kills are caused by dogs running out of control or gone feral.

CONCLUSION

I am not denying the possibility of big cats in the British countryside. There are plenty of prey animals to support a small population of big cats. Even hybrids are possible, albeit unlikely given the genetic problems, under the right circumstances. Personally I am sure there are big cats living wild in the more remote parts of Britain, but for the reasons given above these are more likely to be pure-breds than hybrids and any claimed sightings of hybrids must be treated with caution.