HYBRID MAMMALS
OTHER HYBRID ANIMALS
Although the rest of this site is concerned with feline hybrids, it is worth mentioning some of
the other mammal hybrids which are bred from time to time, either deliberately or by accident.
Hybrids can only occur where the species are closely enough related enough for the egg and
sperm to result in a viable embryo. Where the two species are very closely related, the hybrids
may even been partially or fully fertile. In the laboratory, vole species are sometimes
hybridised during research into genetic traits. Some hybrids are bred for curiosity or public
display, others are bred by researchers involved in genetic researcher and a few occur
naturally - usually where the animals are housed together or where a same-species mate is
not available.
Hybrids are not always reliably reported. In "Mammalian Hybrids" by Annie P Gray (foreword
by Osman Hill), Hill wrote "In the older literature, the claim that an animal is a hybrid has
sometimes had no more solid foundation than that a possibly mutant type happens to have
characters which are a mixture of those of two different species, or that an animal of one
species is found suckling young which bear a strong resemblance to the young of some other
species."
Chimeras are not the same as hybrids (some online sources erroneously define chimera as a
hybrid). Hybrids have intermediate features and each cell is a mix of chromosomes from the
parental species. Chimeras are a mix of genetically different cells to form a mosaic animal.
Details on chimeras can be found at the end of this article.
http://messybeast.com/genetics/hybrid-mammals.html
Page 1
ZOO HYBRIDS
BIG CATS
In "The Variation Of Animals And Plants Under Domestication" Charles Darwin wrote: "Many
species of Felidae have bred in various menageries, although imported from diverse climates
and closely confined. Mr. Bartlett, the present superintendent of the Zoological Gardens
(18/17. On the Breeding of the Larger Felidae 'Proc. Zoolog. Soc.' 1861 page 140.) remarks
that the lion appears to breed more frequently and to bring forth more young at a birth than
any other species of the family. He adds that the tiger has rarely bred; "but there are several
well-authenticated instances of the female tiger breeding with the lion." Strange as the fact
may appear, many animals under confinement unite with distinct species and produce hybrids
quite as freely as, or even more freely than, with their own species." The voluntary
hybridisation of some zoo animals is also referred to as hypersexuality.
The big cat hybrids noted by Darwin are probably the most famous mammal hybrids due to
their impressive size and appearance. Ligers (lion/tiger) and leopons (leopard/lion) are the
best known, along with tigons (tiger/lion). The males are generally sterile and the females are
frequently fertile if bred back to one of the parental species. Other combinations that have
produced live offspring are jaguar/lion, jaguar/leopard, ocelot/puma, ocelot/margay,
puma/leopard and serval/caracal. There are unconfirmed reports of a jaguar/puma hybrid.
Lynx/bobcat hybrids also exist and there are reports of these occurring in the wild where there
was no same species mate available and the animals ended up breeding with the nearest
related species). Some of the female hybrids can be hybridised to yet another species; for
example, a female jaguar/leopard hybrid was mated to a lion and produced offspring (the
offspring resembled leopons).
Some big cat hybrids (ligers, tigons and lepjags) are still bred as curiosities and as exotic pets.
Others, such as leopard/lion and jaguar/lion have not been bred for many years. DNA studies
suggest that Asian and African lions are separate species, although many zoos have mixed the
two in the past, creating "generic" lions. Most white tigers in the USA are subspecific hybrids of
Bengal x Siberian (bengalensis x altaica) subspecies; this is because many zoos breed
"generic" tigers that mix tigers from different subspecies. This site has several illustrated
pages devoted to the big cat hybrids; links can be found at the bottom of this article.
http://messybeast.com/genetics/hybrid-mammals.html
Page 2
CARL HAGENBECK'S HYBRIDS
Carl Hagenbeck Snr, (1810–1887), a Hamburg fishmonger, founded a wild-animal import
business in 1848. In 1863, he opened a menagerie near Hamburg’s harbour. In 1866 Carl
Hagenbeck Jnr (1844–1913) became its manager. The first Hagenbeck Tierpark was set up on
a nearby site in 1874 and, under Hagenbeck Jnr, became the world’s premier wild-animal
dealership. In 1896, Hagenbeck pioneered the "fenceless zoo", using ditches to confine the
exhibits. Performing wild animals remained a major attraction, but were trained through
kindness rather than fear. In 1907, the Tierpark Hagenbeck opened at its present location in
the Stellingen, Hamburg. Though destroyed during air-raids in WWII, it was rebuilt.
Hagenbeck also travelled with his wild animal. On the 18th May 1891, Herr Carl Hagenbeck
gave a show of trained wild beasts - lions, tigers, cheetahs, leopards, bears and boarhounds
(Great Danes) - at the Crystal Palace in London. There was also a Carl Hagenbeck Circus in the
USA, but from 1907 (when Hagenbeck opened his Tierpark) the Indiana-based circus was
owned and operated by Ben E Wallace as the Hagenbeck-Wallace Circus with animals trained
the Hagenbeck way. Hagenbeck sued over the use of his name, but lost the case. The
Hagenbeck-Wallace circus closed in 1938.
Several big cat hybrids were bred, photographed and documented by Hagenbeck in the early
1900s at the Tierpark. He kept records on the success of the pairing, whether or not offspring
were produced and survived and on the hybrids' appearance and fertility. He also produced
hybrids of horses, ponies and zebras and corresponded with James Cossar Ewart regarding the
latter's zebra hybrids. Hagenbeck's experiments helped scientists to understand the
relatedness of certain species and to dispel various myths surrounding inheritance.
His most successful big cat hybrids seem to have been his ligers; these were described in a
letter to Cossar Ewart in December 1900 and they appear to have been used in performances.
Another successful and repeated pairing was that of a puma to a leopardess; a pairing
suggested to him by a small (unidentified) English menagerie. Records from 1900 describe
three sets of twins though only one hybrid survived for any length of time and this showed a
tendency towards miniaturisation, being about half the size of the parents. Hagenbeck
described the puma/leopard mixes as not particularly noteworthy. Hagenbeck also paired a
leopard with a lioness, resulting in live leopon offspring though none survived to maturity. His
pairing of a Bengal tiger with a leopardess in 1900, described in a letter to Cossar Ewart,
resulted in stillborn offspring that had both spots and stripes. The mating was apparently not
repeated since no other information seems to have been reported.
http://messybeast.com/genetics/hybrid-mammals.html
Page 3
BEARS
The black bear and the European brown bear bred in the London Zoological Gardens in 1859,
but the three cubs did not reach maturity. In "The Variation Of Animals And Plants Under
Domestication" Charles Darwin noted: "In the nine-year Report it is stated that the bears had
been seen in the Zoological Gardens to couple freely, but previously to 1848 had most rarely
conceived. In the Reports published since this date three species have produced young
(hybrids in one case) [...]" Hybrids between the brown bear and the grizzly-bear (considereb
by some to be a form of brown bear rather than a species) have been produced in Cologne,
whilst at Halle since 1874 a series of successful matings of polar bears and brown bears have
been made. Examples of these hybrid bears have been exhibited by the London Zoological
Society. The hybrids between the brown and polar bears bred at Halle proved to be fertile,
both with one of the parent species and with one another. Polar bear/Brown bear hybrids are
white at birth but later turn blue-brown or yellow-white.
A male polar bear accidentally got into an enclosure with a female Kodiak (Alaskan Brown)
bear at the US National Zoo in 1936 resulting in three hybrid offspring. One hybrid was named
Willy and grew into an immense specimen. The hybrid offspring were fertile and able to breed
successfully with each other, indicating that the two species of bear are closely related. In the
National Geographic (Vol 137:4, April 1970) article "White Tiger in My House", Elizabeth C
Reed mentions being foster mother to 4 hybrid bear cubs from the National Zoological Park in
Washington where her husband was director. DNA studies have apparently suggested that
some brown bears are more closely related to polar bears than they are to other brown bears,
raising an interesting question as to whether they are truly separate species. All the Ursinae
species (all bears except the giant panda and the spectacled bear) appear able to crossbreed
and will do so if placed together; all have 72 chromosomes except for Spectacled bears (53
chromosomes) and Pandas (42 chromosomes).
C Hart Merriam, taxonomists of grizzly bears, came across one bear that was significantly
different from other grizzlies. Believing it to be a living fossil, he named it Vetularctos
inopinatus ("ancient, unexpected bear"). The bear had been killed in 1864 at Rendezvous
Lake, Barren Grounds, Canada. Merriam described it as "buffy whitish" with a golden brown
muzzle and suggested it came from a separate lineage to the Ursinae, being a modern
descendent of the extinct giant short-faced and relative of the modern spectacled bears. Today
it is variously considered a natural hybrid between a grizzly bear and polar bear or an aberrant
form of grizzly. A similar bear was reported from Kodiak Island. In 1943, Clara Helgason
described a bear seen during her childhood: hunters had shot a large, off-white bear with hair
all over his paws. Some believed it to be a polar bear that had wandered far from its known
range; others claimed it to be an albino Kodiak bear. The presence of hair on the bottom of the
feet suggests it was not a Kodiak brown bear and it may have been a natural hybrid.
More information:
Martin, P.L. 1876. "Ursus arctos and Ursus maritimus. On bastards between these species born
in Nill's menagerie at Stuttgart." Zoologische Garten, 1876:20-22. [Zoologische Garten,
1877:135-136. W. Stendell and E. von Martens, tom. cit., pp.401-402.]
------. 1882. "On a hybrid between a male Ursus maritimus and a female Ursus arctos."
Zoologische Garten, 1882:xxiii, 370.
Kowalska, Z. 1962. "Intergeneric crossbreed of the brown bear Ursus arctos L., and the polar
bear Thalarctos maritimus (Phipps)." Przeglad Zoologiczny, 6:230, 1 pl. [Polish with English
summary.]
------. 1965. "Cross breeding between a female European brownbear and a male polar bear in
Lodz Zoo." Przeglad Zoologiczny, 9:313-319. [Polish with English summary.]
------. 1969. "A note on bear hybrids Thalarctos maritimus and Ursus arctos at Lodz zoo."
International Zoo Yearbook, 9:89.
http://messybeast.com/genetics/hybrid-mammals.html
Page 4
ELEPHANTS
The Asian and African elephants look similar, but are not only different species, they are
different genera i.e. each belongs to a different genus, making them even more distantly
related). Crossbreeds between different genera is regarded as impossible. In 1978, an Asian
elephant cow gave birth to a hybrid calf sired by an African elephant bull. Though the pair had
mated several times, pregnancy was believed to be impossible. The hybrid male calf, "Motty",
had an African elephant's cheek, ears (large with pointed lobes) and legs (longer and
slimmer), but the toenail numbers, (5 front, 4 hind) and the single trunk finger were like
Asians although the wrinkled trunk was like an African. The forehead was sloping with one
dome and two smaller domes behind it. The body was African in type, but had an Asian-type
centre hump and an African-type rear hump. Sadly the calf died of infection 12 days later.
There have also been rumours of three other hybrid elephants, all of which were deformed and
did not survive.
African elephants are divided into 2 species - the Forest elephant and the Savannah elephant.
Though these can hybridise successfully, their preference for different terrains reduces the
opportunities to hybridise and they are genetically distinct from each other. The forest
elephant (Loxodonta africana cyclotis), considered a subspecies of African elephant, has been
raised to species status (Loxodonta cyclotis). Typical savannah elephants have 4 toenails on
each forefoot and 3 on each hind foot. The forest elephant typically has 5 toenails on each
forefoot and 4 on each hind foot. Both species have 5 toenails on all 4 feet at birth - the
number of toenails at maturity is related to wear and tear on different terrain! There are
differences in the shape of the jaw and ears. The forest elephant is considerably smaller and
has thinner, straighter tusks.
A Chinese safari park has a sub-specific hybrid of Malay elephant x Indian elephant.
RHINOS, TAPIRS
A subspecific hybrid white rhino (Ceratotherium s. simum x C s cottoni) was bred at the
Dvurkralv Zoo (Zoological Garden Dvur Kralove nad Labem) in the Czech Republic in 1977.
Hybrid tapirs from Baird's Tapir (T bairdii) and the Lowland Tapir (T terrestris) were bred at
the San Francisco Zoo around 1968 and produced a 2nd generation around 1970.
ANTELOPE
There are a wide variety of Antelope hybrids recorded in zoos, this is generally due to a lack of
more appropriate mates in the enclosure. It also shows how closely related some of the
species are - in fact some are essentially variant populations of the same species and are
prevented from hybridization in the wild by behavioural differences. A mating between a male
Eland and a female Kudu produced a sterile male hybrid that resembled the Eland. Blue
Wildebeest produce fertile hybrids with the smaller Black Wildebeest and this has led to an
entire herd of 180 "genetically contaminated" Black Wildebeest being destroyed in a wildlife
conservation park (rather unfortunate, as "species purity" is a human concept; nature will
exploit the best genes available, even if it means crossing a species boundary). In the early
1900s there were reports that the London Zoological Society had successfully mated several
species of antelopes, for instance, the water-bucks Kobus ellipsiprymnus and Kobus unctuosus,
and the Selouss antelope Limnotragus seloussi with Limnotragus gratus.
The listed hybrids include: Bongo/Sitatunga; Lesser Kudu/Sitatunga; Eland/Greater Kudu; Blue
Duiker/Maxwell's Duiker; Bay Duiker/Red-flanked Duiker; Bay Duiker/ Zebra Duiker; Black
Duiker/Kaffir Duiker; Cape Hartebeest/Blesbok; Bontebok/Blesbok; Black Wildebeest/Blue
Wildebeest; Common Waterbuck/Defassa Waterbuck; Defassa Waterbuck/Nile Lechwe;
Defassa Waterbuck/Kob; Nile Lechwe/Kob; Kafue Lechwe/Ellipsen Waterbuck; Red-fronted
Gazelle/Thomson's Gazelle; Beisa Oryx/Fringe-eared Oryx; Grant's Gazelle/Thomson's Gazelle;
Beisa Oryx/Gemsbok; Arabian Oryx/Scimitar-horned Oryx; Thomson's Gazelle/Roosevelt's
Gazelle; Slender-horned Gazelle/Persian Goitered Gazelle; Persian Gazelle/Blackbuck; Cuvier's
Gazelle/Slender-horned Gazelle.
In zoos, Masai and Rothschild’s Giraffes hybridize and the hybrid "generic" population is
outnumbering the pure-bred populations. This is a problem for conservationists trying to
preserve pure species.
http://messybeast.com/genetics/hybrid-mammals.html
Page 5
PRIMATES
In the primates, many Gibbons are hard to visually identify and are identified by their song.
This has led to hybrids in zoos where the Gibbons were mis-identified. For example, some
collections could not distinguish between Javan Gibbons, Lar Gibbons or Hoolocks and their
supposedly pure breeding pairs were mixed pairs or hybrids from previous mixed pairs. Agile
gibbons have also interbred with these. The offspring were sent to other Gibbon breeders and
led to further hybridization in captive Gibbons. Hybrids also occur in wild Gibbons where the
ranges overlap. Gibbon/Siamang hybrids have occurred in captivity - a female Siamang
produced hybrid "Siabon" offspring on 2 occasions when housed with a male Gibbon; one
hybrid survived, the other didn't. Anubis Baboons and Hamadryas Baboons have hybridized in
the wild where their ranges meet. Different Macaque species can interbreed. In "The Variation
Of Animals And Plants Under Domestication" Charles Darwin wrote: "A Macacus, according to
Flourens, bred in Paris; and more than one species of this genus has produced young in
London, especially the Macacus rhesus, which everywhere shows a special capacity to breed
under confinement. Hybrids have been produced both in Paris and London from this same
genus." In addition, the Rheboon is a captive-bred Rhesus Macaque/Hamadryas Baboon hybrid
with a baboon-like body shape and Macaque-like tail.
Various hybrid monkeys are bred within the pet trade. These include hybrid Capuchins e.g.
Tufted (Cebus apella) x Wedge-capped/weeper (C olivaceus); Liontail macaque X Pigtail
macaque hybrids and Rhesus x Stumptail hybrids. The Japanese macaque (Macaca fuscata)
has interbred with the introduced Taiwanese macacque (M cyclopis); the latter has escaped
into the wild from private zoos. Among African monkeys, natural hybridization is not
uncommon. There numerous field reports of hybrid monkeys and detailed studies of zones
where species overlap and hybrids occur. Among the apes, Sumatran and Bornean orangutans are separate species with anatomical differences, producing sterile hybrids. Hybrid orang
utans are genetically weaker lower survival rates pure animals.
In "The Variation Of Animals And Plants Under Domestication" Charles Darwin noted: "Several
members of the family of Lemurs have produced hybrids in the Zoological Gardens."
MARINE MAMMALS
A hybrid sealion from a cross between the California sealion (Zalophus californianus) and the
South American sealion (Otaria byronia) has also been reported. There has also been a
genetically confirmed harp seal x hooded seal hybrid.
Among the marine mammals, a wolphin (whale/dolphin) hybrid occurred in captivity in 1985
where a female bottlenose dolphin and a male false killer whale shared a pool. The Wholphin's
size, colour and shape are intermediate between the parent species. Named Kekaimalu, she
has 66 teeth - intermediate between a Bottlenose (88 teeth) and False Killer Whale (44 teeth).
The Wholphin proved fertile when she gave birth to a calf sired by a Bottlenose Dolphin; the
calf was three quarters dolphin/one quarter Whale and thus looks more like a dolphin. Despite
being fertile, Kekaimalu did not mother the calf (this is not uncommon in captive dolphins and
was probably not related to her being a hybrid), but it was successfully hand-reared. In April
2005, it was announced that the same wholphin had produced another calf in December 2004.
This second calf was also sired by a Bottlenose dolphin and at 6 months old was already the
size of a 1 year old Bottlenose. The False Killer Whale is not a whale at all, but is a type of
dolphin. Herds of False Killer Whales and Bottlenose Dolphins associate together in the wild
and there are unsubstantiated tales of natural hybrids between the two species.
In 1933, three strange dolphins were beached off the Irish coast; these appeared to be hybrids
between Risso's Dolphin and the Bottlenose Dolphin. This mating has since been repeated in
captivity and a hybrid calf was born. In captivity, a Bottlenose Dolphin and a Rough-Toothed
Dolphin produced hybrid offspring. In the wild, Spinner Dolphins have sometimes hybridised
with Spotted Dolphins and Bottlenose Dolphins. In the wild, bands of males of one dolphin
species have been observed to gang rape a female Spinner. Blue Whales, Fin Whales and
Humpback Whales all hybridise in the wild. Dall's Porpoises and Harbour Porpoises have
hybridized in the wild. There has also been a reported hybrid between a beluga and a narwhal.
http://messybeast.com/genetics/hybrid-mammals.html
Page 6
DOMESTIC ANIMAL HYBRIDS
HORSES, DONKEYS
The various equid hybrids are well known and some are bred commercially. These are the
crosses between various members of the horse family (donkeys, horses and zebras). Mules
(donkey stallion [jack]/horse mare) are bred as draught animals. Male mules are sterile, but
fertile female mules have occurred - they must be bred back to one of the parental species. In
France, the Poitou breed of donkey is used almost exclusively for siring large, strong mules on
Poitou mares. Jack donkeys are reportedly often reluctant to mate with horse mares and may
have to be trained to do so. Although mules are mostly bred as draught animals, miniature
mules are produced using smaller breeds of donkey and similar sized ponies. A female mule is
called a "molly".
A hinny is a horse stallion/donkey mare (jenny or jennet) hybrid, they are less easy to produce
than mules as stallion/jenny matings are less likely to result in pregnancy than jack/mare
matings. These are smaller and finer boned than mules. Part of the size difference was
believed to be due to the jenny having a less roomy womb, but the difficulty in impregnation
suggests it is largely genetic. The head of a hinny looks more similar to that of a horse than
does the head of a mule.
Zedonks (zebronkeys, zonkeys, zebadonks) are zebra stallion/donkey hybrids; zorses are
zebra stallion/horse hybrids and zonies are zebra stallion/pony hybrids. Zorses are sometimes
called golden zebras due to dark stripes overlaying a chestnut background, though the colour
depends on the colour of the horse parent. The zetland is a one off accidental zebra/Shetland
pony hybrid. The term zenkey has been used to describe a hybrid bred in Japan. Zebroid is a
blanket term for zebra/horse hybrids and zebrass indicates a zebra/ass hybrid. Zebrasses tend
to look like donkeys with a striped pattern overlaided on the donkey's background colour. Any
of the zebra species can be used in breeding zebroids; the colour depends on the colour of the
horse; usually there is clear striping on the legs, a dorsal stripe, striped face and less distinct
stripes on the body; the somewhat donkey-like attributes of zebras result in a dorsal stripe,
upright mane without a forelock and large ears.
Another term for zebra hybrids is zebra mule since zebra stallions (which are hand-raised or
fostered on a horse mare) are used in preference to zebra mares. Zebra hinnies are rarely
found. Zebroid and zebrass males are generally sterile. Although wild animals, zebras which
are hand-reared or reared with domestic horses can become tame enough to be led, ridden or
used as draught animals. A breeding programme at Colchester Zoo in 1975 resulted in several
hybrids. In Christmas week of 1975 their third zedonk foal was born; the result of mating a
donkey with different male zebras. Previous attempts at crossbreeding zebras with horses and
donkeys had failed to produce surviving foals. The aim was to produce disease-resistant workhorses for Africa. Colchester Zoo experts believed their success was due to the use of an
Arabian donkey (a variety not tried before in hybridization experiments) and were hopeful that
the hybrids would be viable and fertile.
Usually a zebra stallion is paired with a horse mare or ass mare, but in 2005, a Burchell's
zebra named Allison produced a zebrass called Alex sired by a donkey at Highland plantation in
St. Thomas parish, Barbados.
http://messybeast.com/genetics/hybrid-mammals.html
Page 7
1899 zebra/horse hybrid
1899 zebra/horse hybrid
1904 zebra/horse hybrid
1970s zebra/donkey hybrid
Cossar Ewart, Professor of Natural History at Edinburgh (1882-1927) and a keen geneticist,
crossed a zebra stallion with pony mares in order to disprove telegony, or paternal impression,
a common theory of inheritance at the time. Telegony states that if a female mates with more
than one male the later offspring will inherit characteristics from the earlier sires.
Shadow the zedonk at
Colchester Zoo (2005)
http://messybeast.com/genetics/hybrid-mammals.html
Page 8
Shadow rolling, showing the
ventral (belly) stripe.
Right: Showing the markings on
the back of the ears.
This explanation of Paternal Impression, or "Telegony", is taken from the 1896 work
"Anomalies and Curiosities of Medicine" by George M Gould and Walter L Pyle. It cites cases in
horses/zebras, dogs and cat; the latter relating to long-haired cats appearing in litters born to
short-haired parents (actually due to recessive genes).
The influence of the paternal seed on the physical and mental constitution of the child is well
known. To designate this condition, Telegony is the Word that was coined by Weismann in his
"Das Keimplasma," and he defines it as "Infection of the Germ," and, at another time, as "
Those doubtful instances in which the offspring is said to resemble, not the father, but an early
mate of the mother," - or, in other words, the alleged influence of a previous sire on the
progeny produced by a subsequent one from the same mother. In a systematic discussion of
telegony before the Royal Medical Society, Edinburgh, on March 1, 1895, Brunton Blaikie, as a
means of making the definition of telegony plainer by practical example, prefaced his remarks
by citing the classic example which first drew the attention of the modern scientific world to
this phenomenon. The facts of this case were communicated in a letter from the Earl of Morton
to the President of the Royal Society in 1821, and were as follows:
In the year 1815 Lord Morton put a male quagga [a type of zebra] to a young chestnut mare
of seven eighths Arabian blood, which had never before been bred from. The result was a
female hybrid which resembled both parents. He now sold the mare to Sir Gore Ousley, who
two years after she bore the hybrid put her to a black Arabian horse. During the two following
years she had two foals which Lord Morton thus describes: " They have the character of the
Arabian breed as decidedly as can be expected when fifteen sixteenths of the blood are
Arabian, and they are fine specimens of the breed; but both in their color and in the hair of
their manes they have a striking resemblance to the quagga. Their color is bay, marked more
or less like the quagga in a darker tint. Both are distinguished by the dark line along the ridge
of the back, the dark stripes across the forehand and the dark bars across the back part of the
legs." The President of the Royal Society saw the foals and verified Lord Morton’s statement.
Cossar Ewart found that zebra-horse hybrids were brown with faint stripes. When the same
mares were subsequently mated with a pony, the resulting foals showed none of the markings
or temperamental characteristics of a zebra. Cossar Ewart found that in male zebra-hybrids
the sexual cells were immature and the sperm were abnormal, however the ovaries of female
zebra-hybrids appeared similar to those of a normal mare or female zebra. As well as
disproving paternal impression, he wanted to produce a more resilient draught animal for
South Africa; one less subject to local diseases and more tractable than a mule.
http://messybeast.com/genetics/hybrid-mammals.html
Page 9
During the South African War, an attempt was made
by the Boers to evolve a new animal to supplement
the supply available for transport work. A cross was
obtained between a Chapman's zebra and a pony
and a specimen was captured by the British and
presented to King Edward VII by Lord Kitchener. The
animal was produced chiefly for hauling guns. It was
photographed by W S Berridge. ("Wonders of Animal
Life" edited by J A Hammerton (1930))
"Ass-zebra" ("Wonders of Animal Life"
edited by J A Hammerton (1930))
In "Origin of Species" (1859) Charles Darwin mentioned four coloured drawings of hybrids
between the ass and zebra. He continued "In Lord Moreton's famous hybrid from a chestnut
mare and male quagga, the hybrid, and even the pure offspring subsequently produced from
the mare by a black Arabian sire, were much more plainly barred across the legs than is even
the pure quagga. Lastly, and this is another most remarkable case, a hybrid has been figured
by Dr. Gray (and he informs me that he knows of a second case) from the ass and the
hemionus." Darwin described the latter hybrid in "The Variation Of Animals And Plants Under
Domestication": The Equus indicus [onager] a hybrid, raised at Knowsley ('Gleanings from the
Knowsley Menageries' by Dr. J.E. Gray.) from a female of this species by a male domestic ass,
had all four legs transversely and conspicuously striped, had three short stripes on each
shoulder and had even some zebra-like stripes on its face! Dr. Gray informs me that he has
seen a second hybrid of the same parentage, similarly striped.
In his "The Variation Of Animals And Plants Under Domestication", Darwin wrote: "I have seen,
in the British Museum, a hybrid from the ass and zebra dappled on its hinder quarters. [...]
Many years ago I saw in the Zoological Gardens a curious triple hybrid, from a bay mare, by a
hybrid from a male ass and female zebra. and further described Moreton's hybrid; In the
famous hybrid bred by Lord Morton ('Philosoph. Transact.' 1821 page 20.) from a chestnut,
nearly purely-bred, Arabian mare, by a male quagga, the stripes were "more strongly defined
and darker than those on the legs of "the quagga." The mare was subsequently put to a black
Arabian horse, and bore two colts, both [...] plainly striped on the legs, and one of them
likewise had stripes on the neck and body.
In that book, Darwin concluded: "The ass has a prepotent power over the horse, so that both
the mule and the hinny more resemble the ass than the horse; but that the prepotency runs
more strongly in the male-ass than in the female, so that the mule, which is the offspring of
the male-ass and mare, is more like an ass, than is the hinny, which is the offspring of the
female-ass and stallion." In "The Variation Of Animals And Plants Under Domestication" Darwin
elaborated: "Colin, who has given in his 'Traite Phys. Comp.' tome 2 pages 537-539, [...] is
strongly of opinion that the ass preponderates in both crosses, but in an unequal degree. This
is likewise the conclusion of Flourens, and of Bechstein in his 'Naturgeschichte Deutschlands' b.
http://messybeast.com/genetics/hybrid-mammals.html
Page 10
1 s. 294. The tail of the hinny is much more like that of the horse than is the tail of the mule,
and this is generally accounted for by the males of both species transmitting with greater
power this part of their structure; but a compound hybrid which I saw in the Zoological
Gardens, from a mare by a hybrid ass-zebra, closely resembled its mother in its tail.)"
In "Darwinism An Exposition Of The Theory Of Natural Selection With Some Of Its Applications"
(1889), Alfred Russel Wallace commented: "Crosses between the two species of zebra, or even
between the zebra and the quagga, or the quagga and the ass, might have led to a very
different result."
Hybrid of Grevy's Zebra and Somali Ass (1929)
An experiment that disproved telegony. Left, a striped zebra-horse hybrid, produced by
mating a mare with a zebra stallion. The same mare was then mated with a horse stallion,
and produced the filly shown below, which bears no traces of any effect of the previous sire.
The experiment was carried out by the US Government and reported in "Genetics in Relation
to Agriculture" by E B Babcock and RE Clausen. ("The Science of Life" by H G Wells, J Huxley
and GP Wells (c.1929))
In "The Science of Life" (c 1929) by H G Wells, J Huxley and GP Wells, the authors wrote "Today it is possible to assert without any question that telegony is a mere fable, which could only
have gained ground in the days when men were ignorant of the true mechanism of fertilization
and reproduction. The supposed instances of telegony which are constantly being reported
even to-day, invariably. Perhaps the most famous example is that of Lord Morton’s mare. The
mare, a pure Arabian, was mated with a zebra stallion, and produced a hybrid foal. On two
http://messybeast.com/genetics/hybrid-mammals.html
Page 11
later occasions, she was bred to a black Arab stallion, and gave birth to two further foals.
These had legs which were striped even more definitely than those of the hybrid foal or the
zebra sire himself, and one had some stripes on parts of the neck also. In addition, they had a
stiff mane of very zebra-like appearance. Darwin himself accepted the evidence as sufficient
proof of telegony. But when definitely planned and long-continued experiments were made,
the proof escaped. Cossar Ewart, for instance, made a number of horse and zebra crosses to
test the validity of the belief. When mares previously bred to zebras were afterwards mated
with horse stallions, their colts were often without the least trace of zebra characters. In other
cases, colts with some degree of striping were produced. But one mare gave birth to a striped
colt as a result of her first mating, which was with a horse stallion ; while two later matings
with other stallions, made after she had been successfully mated once and three times
respectively with a zebra, gave unstriped offspring. In other cases, when striped colts were
born to a mare and stallion after the mare had been previously mated to a zebra, Ewart took
other mares, closely related to the first, bred them to the same Arabian stallion without having
mated them previously with a zebra - and they, too, produced striped foals. In short, the
production of striping (and also of erect mane) in foals is not a very uncommon occurrence in
horses; it may appear whether previous impregnation by a zebra has taken place or not. The
stripes of Lord Morton’s foals were a mere coincidence, well illustrating the danger of drawing
conclusions from single and therefore possibly exceptional cases, and the need for systematic
and repeated experiments."
FERTILE MULES
Although mules are generally reckoned to be sterile, this is not a hard and fast rule. Several
female mules have produced offspring when mated to a purebred horse or ass. Since 1527
there have been more than 60 foals born to female mules around the world and probably
additional ones that have not been documented. Donkeys have 62 chromosomes while horses
have 64 chromosomes. As well as different numbers, the chromosome have different
structures. Mules and hinnies have 63 chromosomes that are a mixture of one from each
parent. The different structure and number usually prevents the chromosomes from pairing up
properly and creating successful embryos.
Cornevin and Lesbre stated that in 1873 an Arab mule was fertilized in Africa by a stallion, and
produced female offspring. Borh parents and the offspring were taken to the Jardin
d'Acclimatation in Paris where the mule had a second female colt sired by the same stallion
and then two male colts, one sired by an ass and the other by a stallion. The female progeny
were fertile, but their offspring were feeble and died at birth. Cossar Ewart gives an account of
a recent Indian case in which a female mule gave birth to a male colt. The best documented
fertile mule mare was "Krause" who had two male offspring, both sired by her own sire. In
most fertile mule mares, the mare passes on a complete set of her maternal genes (i.e. from
her horse/pony mother) to the foal; a female mule bred to a horse will therefore produce a
100% horse foal. In the 1920s, "Old Beck" (Texas A&M) produced a mule daughter called
"Kit". When Old Beck was bred to a horse stallion she produced a horse son (he sired horse
foals). When bred to a donkey, she produced mule offspring. Likewise, a mare mule in Brazil
has produced two 100% horse sons sired by a horse stallion.
A fertile hinny in China is believed to be a unique case. Her offspring was sired by a donkey.
Named "Dragon Foal", one would have expected a donkey foal if the mother had passed on her
maternal chromosomes in the same way as a mule. However, Dragon Foal appears to be a
strange donkey with some mule-like features. Her chromosomes and DNA tests confirm that
she is a previously undocumented combination. In Morocco, a mare mule produced a male foal
that is 75% donkey and 25% horse i.e. she passed on a mixture of genes instead of passing
on her maternal chromosomes in the expected way. There are no recorded cases of fertile
mule stallions. There is an unverified case of a mare mule that produced a mule daughter. The
daughter was also fertile and produced a horse-like foal with some mule traits; this was
dubbed a "hule". There are no reports as to whether the hule was fertile; mule stallions are
generally castrated to make them tractable and, if the hule was treated the same way as
mules, the opportunity to test for fertility would have been lost.
http://messybeast.com/genetics/hybrid-mammals.html
Page 12
DOG FAMILY
The dog family is also capable of interbreeding and producing fertile offspring. People wanting
to improve domestic dogs have sometimes bred them back to wolves; as well as compensating
for genetic problems in domestic dogs, the wolf-dog hybrids tend to be dominant and less
domesticable. Grey wolves have been crossed with wolf-like dogs e.g. German Shepherds,
Malamutes. Many become a problem in adulthood, usually because the owner expects them to
act like a domestic dog and is not prepared for their more wolf-like behaviour. The Saarloos
breed is derived from such crosses. Parts of Europe, the wolf naturally hybridises with stray
domestic dogs resulting in mongrel populations. The Australian Dingo (a feral, rather than wild,
species) also hybridises freely with domestic dogs.
An unconfirmed female fox-dog hybrid (terrier/fox) has been reported in the UK, unfortunately
it was euthanized when the owner died because no suitable home could be found for it.
Although gamekeeper folklore claims that Terrier bitches can produce offspring with dog Foxes,
there are no authenticated hybrids between domestic dogs and Red Foxes. According to
anecdote, "dox" (fox/bitch) hybrids are stronger and more vigourous than either parent and
can be bred to other doxes. Thus far, all reported dox hybrids have turned out to be natural
variation in the domestic dog. The great genetic mismatch between red foxes and domestic
dogs makes the dox hybrid no more real than a cabbit (cat-rabbit) hybrid.
There has been a reported cross between a domestic dog and a South American fox, but the
latter was most likely a fox-like wolf and not a true fox.
There was a report of a dox in Saskatchewan, Canada. This was believed to be the result of a
miniature sheltie bitch with a wild fox (fox species not identified). One out of the three
offspring survived, this being a sterile female that resembled a fox. However, the variability of
dogs in appearance make it impossible to determine whether an animal is hybrid based on
looks alone. I have not found genetic evidence to support the hybrid identity.
Coy-dogs (male coyote/female dog) have occurred e.g. a Coyote/Irish Setter mix (resembling
a liver-coloured, spaniel-like dog) has been reported. Coydogs were once believed to be
present in large numbers in Pennsylvania due to Coyotes being in decline and domestic dogs
being available as mates. Most were probably naturally occurring red or blond Coyotes or feral
dogs. The breeding cycles of dogs and coyotes are not synchronized and studies indicate that
Coyote-Dog interbreeding is uncommon. If it such interbreeding was common, the Coyote
population would acquire more and more dog-like traits. Coyotes have also been crossed with
Australian dingoes (this cross was made at the time the dingo was considered to be different
species to the domestic dog).
Coy-wolves (Coyote/Wolf) have occurred in captivity or, rarely, in the wild where the choice of
same-species mates has been limited. Coyote/Red Wolf hybrids have been found. Some
consider the American Red Wolf is not to a true species because it can hybridize with both the
Grey Wolf and the Coyote; however it is now known that hybridization between species (in
general) happens more often than previously thought. Some consider it a Grey Wolf/Coyote
hybrid and use this argument to prevent conservation of the Red Wolf. Some hybridization
occurred when pure Red Wolves were in decline and interbred with more numerous Coyotes.
More recent studies in many mammals shows that true species can and do hybridize and that
the species boundary is preserved by geographic or behavioural separation, not by genetic
separation. The converse mating results in a Dogote and there is currently one known Dogote
which arose from a male German Shepherd/female coyote mating in the wild. Hybrid pups
were found after a female coyote was shot. The adult Dogote resembled a German Shepherd
in colour.
The Wolf and Jackal (an African wild dog) can interbreed and produce fertile hybrid offspring.
In Russia, Dog/Jackal hybrids were bred as sniffer dogs because Jackals have a superior sense
of smell and Huskies are good cold climate dogs. Male Jackal pups had to be fostered on a
Husky bitch in order to imprint the Jackals on dogs. Female Jackals accepted male Huskies
http://messybeast.com/genetics/hybrid-mammals.html
Page 13
more easily. The half-bred Jackal-Dogs were hard to train and were bred back to Huskies to
produce quarter-bred hybrids (quadroons). These hybrids were small, agile, trainable and had
excellent noses. They are called Sulimov Dogs after their creator and may one day be
registered as a working breed of dog.
This extract from the "Book of The Dog" by William Youatt (1846) demonstrates nineteenth
century beliefs about hybridisation between different species. It was known that a dog and
wolf could be crossed and that the union would produce vicious mongrels, but there were
claims of hybrids now known to be impossible: "There are some naturalists that even go so far
as to state that the different varieties of dogs are sprung from, or compounded of, various
animals, as the hyaena, jackal, wolf, and fox. The philosophic John Hunter commenced a series
of experiments upon this interesting subject, and was forced to acknowledge that "the dog
may be the wolf tamed, and the jackal may probably be the dog returned to his wild state. The
ancient Cynegetical [dog] writers were not only acquainted with the cross between the wolf
and dog, but also boasted the possession of breeds of animals, supposed to have been derived
from a connection with the lion and tiger. The Hyrcanian dog, although savage and powerful
beast, was rendered much more formidable in battle, or in conflict with other animals, by his
fabled cross with the tiger. In corroboration of this singular, but not less fabulous belief, Pliny
states that the inhabitants of India take pleasure in having dog bitches lined by the wild tigers,
and to facilitate this union, they are in the habit of tieing them when in heat out in the woods,
so that the male tigers may visit them."
In "Origin of Species" (1859) Charles Darwin wrote The German Spitz dog unites more easily
than other dogs with foxes [...] certain South American indigenous domestic dogs do not
readily cross with European dogs ..." and in "Darwinism An Exposition Of The Theory Of
Natural Selection With Some Of Its Applications" (1889), Alfred Russel Wallace commented:
"Dogs have been frequently crossed with wolves and with jackals, and their hybrid offspring
have been found to be fertile _inter se_ to the third or fourth generation, and then usually to
show some signs of sterility or of deterioration." (The deterioration was due to inbreeding
among the hybrid offspring)
In "The Variation Of Animals And Plants Under Domestication" Charles Darwin wrote: "Buffon
got four successive generations from the wolf and dog, and the mongrels were perfectly fertile
together. [...] M. Flourens states positively as the result of his numerous experiments that
hybrids from the wolf and dog, crossed inter se, become sterile at the third generation, and
those from the jackal and dog at the fourth generation [attributed to inbreeding]. ('De la
Longevite Humaine' par M. Flourens 1855 page 143. Mr. Blyth says ('Indian Sporting Review'
volume 2 page 137) that he has seen in India several hybrids from the pariah-dog and jackal;
and between one of these hybrids and a terrier. The experiments of Hunter on the jackal are
well-known. See also Isid. Geoffroy St.-Hilaire, 'Hist. Nat. Gen.' tome 3 page 217, who speaks
of the hybrid offspring of the jackal as perfectly fertile for three generations.) [...] Mr. Philip P.
King, after ample opportunities of observation, informs me that the Dingo and European dogs
often cross in Australia. [...] Several years ago I saw confined in the Zoological Gardens of
London a female hybrid from an English dog and jackal, which even in this the first generation
was so sterile that, as I was assured by her keeper, she did not fully exhibit her proper
periods; but this case was certainly exceptional, as numerous instances have occurred of
fertile hybrids from these two animals. [...] We have already seen how often savages cross
their dogs with wild native species; and Pennant gives a curious account ('History of
Quadrupeds' 1793 volume 1 page 238.) of the manner in which Fochabers, in Scotland, was
stocked "with a multitude of curs of a most wolfish aspect" from a single hybrid-wolf brought
into that district. [...] the jackal is prepotent over the dog, as is stated by Flourens, who made
many crosses between these animals; and this was likewise the case with a hybrid which I
once saw between a jackal and a terrier. "
http://messybeast.com/genetics/hybrid-mammals.html
Page 14
CAT FAMILY
Domestic cats have been crossed with a wide variety of small wild species of cat e.g. African
Wildcat, European Wildcat, Geoffroy's Cat, Jungle Cat, Margay, Fishing Cat, Asian Leopard Cat,
Serval, Caracal, Lynx plus unconfirmed reports of hybrids with Pallas's Cat and the RustySpotted Cat. Some of these have been developed into domestic cat breeds by breeding out the
wildness, but retaining the colour/pattern and size. Contrary to rumour (and hype from less
scrupulous breeders) the Bengal cat is NOT a cat/leopard hybrid; it is a hybrid of domestic cat
and Asian Leopard Cat (a small wildcat species). Margay/domestic hybrids were absorbed into
the Bengal breeding programme. Because the Margay and Ocelot can be crossed, the ocelot
could, in theory, produce hybrids with domestic cats.
F. tigrina, the Tiger Cat (Little Spotted Cat/Oncilla) can interbreed although most offspring are
stillborn. An Oncilla was accidentally and successfully bred with Abyssinian cats by Dutch cat
specialist Mme Falken-Rohrle. A small cross-breed kitten was born as the result of an Oncilla x
Abyssinian mating. Three more cross-breed kittens were bred from a repeat mating. Geoffroy's
Cat (F. geoffroyii) have been crossed with domestic cats to produce fertile hybrids called
"Safari Cats". Domestic cats have been crossed with the Fishing cat (F viverrina) to produce
the "Machbagral" and "Viverral" breeds though infertility is a problem with the F1 hybrid
males. The Black-footed cat (F. nigripes) will breed with both domestic cats and F. lybica,
fertility of offspring is not recorded. There are unconfirmed reports that the Rusty-Spotted cat
(F rubiginosa) interbreeds with domestic cats, but too little is known about this species to be
certain. The German naturalist Peter Pallas, who discovered Pallas's Cat (F manul), recorded
that it would breed with domestic cats, but this has not been attempted in captivity.
Serval males raised with domestic females will mate them, though the pregnancy is not always
successful and human intervention may be necessary to raise the hybrid "Savannah" kittens.
The F1 females are fertile, but the male hybrids of the first three or four generations are
usually infertile. In 1998, I Kusminych and A Pawlowa reported a caracal/domestic hybrid cat
at Moscow Zoo. Servals and caracals are hybridised for the exotic pet market. The Bobcat (F
Rufus) will hybridise with domestic cats and several new breeds are being developed from such
hybrids e.g the American Lynx is a hybrid of Bobcat and domestic Manx. There are several
reputed Lynx/domestic hybrids, but only one confirmed hybrid. As there are Bobcat/domestic
hybrids and also Lynx/Bobcat hybrids, Lynx/domestic cat interfertility is not unexpected.
Existing wild/domestic hybrids are being further hybridised with each other and with other wild
species There are plans to mate domestic females with a male Jaguarundi, but it isn't yet
known if the mating will result in offspring.
FELINE HYBRIDS AND KARYOTYPES
A factor influencing fertility of hybrids is the chromosome complement (karyotype).
Geoffroy's cat (and the related Tiger Cat and the larger Margay and Ocelot) has 36
chromosomes. The domestic cat and its relatives have 38 chromosomes. The F1 hybrid
offspring of the Geoffroy's Cat and a domestic cat have 37 chromosomes - 18 from the
Geoffroy's cat parent and 19 from the domestic cat parent. One could reasonably expect these
offspring to be infertile. In fact feline hybrids have proven remarkable fertile with most female
hybrids being able to breed with either parent species. The male hybrids are less likely to be
fertile. Some of the second generation F2 hybrids (i.e. F1 hybrid is back-crossed to the parent
species, usually to the domestic cat to create a domestic-type temperament) also have 37
chromosomes while others have a count of 38. This is apparently because the F1 hybrids are
heterozygous, and can produces eggs or sperm containing either 19 chromosomes or 18
chromosomes. F1 hybrids tend to be large while F2 and later generations are the same size as
domestic cats. By testing for chromosome count, it is theoretically possible to select and breed
hybrid cats which consistently have 38 chromosomes (like the wild ancestor) to maintain the
size and appearance of the initial hybrid.
http://messybeast.com/genetics/hybrid-mammals.html
Page 15
FARM LIVESTOCK HYBRIDS
CATTLE
Among bovines, American Bison bulls (American "Buffalo") have been crossed with domestic
cattle to produce Beefalo and Cattalo. These are very variable in type and colour depending on
the breed of cattle used e.g. Herefords and Charolais (beef cattle), Holsteins (dairy) or
Brahmin (humped cattle). Generally they are horned with heavy set forequarters, sloping
backs and lighter hindquarters. Beefalo have been back-crossed to Bison and to domestic
cattle; some of these resemble pied Bison with smooth coats and a maned hump. The aim is to
produce high protein, low fat and low cholesterol beef on animals which have "less hump and
more rump". Although Bison bull/domestic cow crossings are more usual, domestic bull/Bison
cow crossings have a lower infant mortality rate (cow immune systems can reject hybrid
calves). Modern Beefalo include fertile bulls, making the Beefalo a variety of "improved cattle"
with a dash of Bison. There were suggestions of crossing the beefalo to Cape buffalo. Below
are images of bull and cow cattalos (from "Wonders of Animal Life" edited by J A Hammerton
(1930)
The Zubron (below) is a hybrid between a domestic cow and a Wisent (European Bison, Bison
bonasus). As such it is analogous to the American Beefalo or Cattalo. The first Zubrons were
created by Leopold Walicki in 1847, although earlier natural hybrids might have occurred
where cattle were introduced into the Wisent's habitat. After World War I, the Zubron was
considered as a possible replacement for domestic cattle as they were durable and resistant to
many cattle diseases. They also thrived on poor pasture, in harsh weather and with minimal
husbandry. After World War II and between 1958 and the late 1980s, Zubron herds were bred
and maintained by the Polish Academy of Sciences in various laboratories, notably those at
Bialowieza and Mlodzikowo. The aim was to create a hardy and cost-effective replacement for
cattle and although this aim was achieved, the breeding experiments ceased in the late 1980s.
there are only a few remaining Zubrons and these can be found at Bialowieski National Park.
Zubrons are heavy animals and larger than Wisents. The males weigh up to 1200 kg and
females weigh up to 810 kg. First generation Zubron males are infertile and cannot be used for
breeding, but the females are fertile and may be bred back (back-crossed) to either Wisent or
to domestic bulls. Males from these back-crosses are fertile.
http://messybeast.com/genetics/hybrid-mammals.html
Page 16
The Bison (American "Buffalo") has also been bred with the domestic Tibetan Yak to create the
Yakalo. In Nepal, Yak/Cow hybrids are bred using Yak bulls on domestic cows or, less often,
domestic bulls on Yak cows. The Yak-Cow females are fertile, the males are sterile and the
meat is considered superior to beef. In Nepalese, the hybrid is called a Khainag or Dzo
(male)/Dzomo (female). A Dzomo crossed with either a domestic bull or yak bull results in an
Ortoom (three-quarter-bred) and an Ortoom crossed with a domestic bull or yak bull results in
a Usanguzee (one eighth bred). As a result, many supposedly pure Yak and pure cattle
probably carry a dash of each other's genetic material. There have apparently been hybrids
between the American Bison and European Bison (Wisent)
A herd of hybrid plains bison x wood bison apparently lived wild in the Yukon, Canada. The
Wood bison is a distinct subspecies that almost became extinct in the 20th century. In an
attempt to save the Plains bison subspecies, between 1925 and 1928, thousands of Plains
bison were released into Wood Buffalo Park (a preserve for the Wood buffalo subspecies). They
readily interbred and produced a 12,000 strong herd by 1934. The Wood bison was apparently
hybridised into extinction, though a small genetically pure herd was recovered from an isolated
area in 1959 and is now being kept isolated from introduced Plains bison.
In "The Variation Of Animals And Plants Under Domestication" Charles Darwin wrote: "Bos
primigenius and longifrons have been ranked by nearly all palaeontologists as distinct species;
and it would not be reasonable to take a different view simply because their domesticated
descendants now intercross with the utmost freedom. All the European breeds have so often
been crossed both intentionally and unintentionally, that, if any sterility had ensued from such
unions, it would certainly have been detected. [...]The late Lord Powis imported some zebus
[Indian humped cattle] and crossed them with common cattle in Shropshire; and I was
assured by his steward that the cross-bred animals were perfectly fertile with both parentstocks. Mr. Blyth informs me that in India hybrids, with various proportions of either blood, are
quite fertile; and [...] are allowed to breed freely together."
Water Buffalo and Domestic Cattle cannot hybridize; the embryos fail around the 8-cell stage.
http://messybeast.com/genetics/hybrid-mammals.html
Page 17
OTHER HYBRIDS AND CHIMERAS
HUMANZEES
A reputed "humanzee" (human/chimp hybrid) called Oliver was DNA tested and found to be a
chimpanzee, albeit one which slightly differed genetically from the more familiar chimps in
being bipedal and having a smaller head. Oliver may have been a mutant or represent an
unknown species of ape. It is currently believed that he represents a geographical subspecies
of chimpanzee. He did not associate with other chimps in captivity as was sexually attracted to
human women instead. This meant he was never bred. Oliver's habitual bipedal gait is now
believed to be a result of early training and habit, although he mastered it to a greater degree
than most trained chimps. It's worth remembering that evolution is a never-ending process
and that it's possible for bipedalism to develop in other apes. In a publicity event, a woman
declared her willingness to be inseminated by Oliver (and even to have the mating filmed for
scientific purposes), but this offended public sensibilities and did not happen. Had Oliver been
a genuine hybrid, then like most male hybrids he would probably have been sterile anyway.
There have been persistent rumours of a Chinese humanzee experiment; the rumoured 3
month foetus died when the mother was killed during civil unrest. There are similar rumours of
a humanzee or manpanzee experiment in the USA. In the 1960s there were persistent
rumours of a Russian experiment to inseminate either a female chimpanzee or a female gorilla
with human sperm. Another unknown ape (the Koolakamba) has been reported in Africa and
claimed to be a Gorilla/Chimp hybrid. Larger, flatter faced, larger skulled and more bipedal
than a chimp, it may also be a mutation, in which case we are witnessing evolution in action.
In the 19th century, a Khoisan (Hottentot) woman called Saartjie Baartman was exhibited in
Europe in a cage. Negro women with enlarged labia and enlarged buttocks were sometimes
deemed evidence of chimp/human hybridisation; such hybrids being called a "womanzee". This
was based on the supposed resemblance of their genitalia to those of female chimps and fitted
with the then prevalent opinion that Negroes were inferior, or less evolved, than Europeans.
Enlarged buttocks occur due to a condition called steatopygia (extreme accumulation of fat on
the buttocks), while enlarged labia, or "Hottentot Apron" can be either inherited or
induced/enhanced by manual stretching (in some regions they were considered attractive).
Neither trait is due to hybridisation.
The idea of human/ape hybrids has fascinated people and resulted in several films or TV
series, some exploring whether such hybrids would have "human rights" or simply be
experimental animals for use in vivisection. It is only a matter of time before curiosity
overcomes ethics and an authenticated attempt is made.
http://messybeast.com/genetics/hybrid-mammals.html
Page 18
CHIMERAS
Chimeras are not really hybrids, but are organisms containing cells from different "parents".
The Geep (mentioned earlier) was made by merging a sheep embryo with a goat embryo. Each
population of cells keeps its own character and the animals is a mosaic of mis-matched parts.
An analogy is two jigsaw puzzles cut using an identical cutter, but with different pictures. You
can make a single puzzle out of the mis-matched parts, but the completed puzzle will show
parts of both different pictures.
Interspecies chimeras are made in the laboratory. There have been rat/mouse chimeras and
recently a rabbit/human mix (it was not allowed to develop beyond a few days). Like hybrids,
the parent species must be closely enough related if the jigsaw-puzzle offspring is to be born
alive and relatively healthy. The chimeras have either 4 parents (2 fertilized eggs are fused
together) or 3 parents (a fertilized egg is fused with an unfertilized egg or a fertilized egg is
fused with an extra sperm).
In nature, chimeras sometimes form when twin embryos fuse together in the womb during
pregnancy. This is not detected unless the offspring has visible abnormalities (e.g. some
tortoiseshell male cats or ambiguous sex organs) or behavioural abnormalities (e.g. confused
gender behaviour). Recent studies of tortoiseshell male cats and unusually coloured cats
(containing a mix of coloured patches considered genetically impossible) suggest that natural
chimerism is more common than previously realised and that it frequently goes undetected.
In April 2005 , scientists at the University of California created a human-cat chimera. Far from
creating an "anthro-cat", they fused the feline Fel d 1 protein (the protein that triggers the
allergic reaction in cat allergy sufferers) with a human protein known to suppress allergic
reactions. When tested in mice, the chimeric protein stifled cat allergy. The feline part of the
protein binds to the specific immune cells that generate the allergic reaction to Fel d 1. The
human part of the protein also binds to the immune cells and tells them to stop reacting.
Because the human part is more dominant, the allergic reaction is halted. Chimeric proteins
could be used to desensitise allergy sufferers by retraining their immune system.
http://messybeast.com/genetics/hybrid-mammals.html
Page 19
CROSSING THE SPECIES BOUNDARY
Speciation (one species evolving into two) is usually a slow process. It is generally accepted
that different species usually cannot mate and reproduce - this is called "reproductive
isolation". The exception was closely related species which can produce hybrids, although
those hybrids have reduced fertility. The more easily two species form hybrids, the more
closely the species are related in evolutionary terms. However, nature defies human attempts
to compartmentalize creatures into static species. Hybridization is turning out to be more
common than previously realised.
One way reproductive isolation occurs is changes in genes due to mutation. One group of
animals might be geographically isolated from others of the same species. Each group
undergoes slightly different mutations over many generations - some genes affect appearance,
others affect behaviour. Many generations later, the two groups become different enough that
even if they can mate, they can't produce fully fertile offspring.
Sometimes, one species can split into two through behavioural isolation. Some individuals
develop behaviour patterns which limit their choice of mates e.g. they might be attracted to
certain colours or might be active at different times of day. Though they are fully capable of
interbreeding with the other group, their different behaviours keep them apart. If their habitat
became permanently overcast, those behaviour barriers would break down and they would
interbreed freely; their hybrids might become new species.
Another way reproductive isolation occurs is when fragments of DNA accidentally jump from
one chromosome to another in an individual (chromosomal translocation) The mutant
individuals cannot reproduce except with other mutant individuals - not much good unless the
individual has mutant siblings to mate with! There are also "master genes" which govern
general body plan (Hox genes) and those which switch other genes on and off. A small
mutation to a master gene can mean a sudden big change to the individuals that inherit that
mutation. Sometimes, those radical mutations can "undo" generations of evolution so that two
unrelated species can mate with each other and produce fertile young (so far, this has only
been seen in micro-organisms).
Hybridisation is usually considered a dead end because the hybrids are not fully fertile; if they
are fertile, the hybrids are usually absorbed back into the population of one or other parent
species and most of the alien genes are bred out. More rarely, hybrids can become new
species or new sub-species. In the hands of breeders, some domestic/wildcat hybrids can
become breeds; these are not new species because the wildcat genes are largely bred out by
crossing with domestic cats, until only the wildcat pattern remains.
In some species, hybridisation plays an important role in evolutionary biology. Most hybrids
face handicaps as a result of genetic incompatibility, but the fittest survive, regardless of
species boundaries and may contain a combination of traits which allows them to exploit new
habitats or to succeed in a marginal habitat where the two parent species have trouble
surviving (seen in some sunflowers). Unlike mutation, hybridisation creates variations in many
genes or gene combinations simultaneously. Some successful hybrids could evolve into new
species within 50-60 generations. Life may be a genetic continuum rather than a series of selfcontained species.
Usually, where there are two closely related species living in the same area, less than 1 in
1000 individuals will be hybrids because animals rarely choose a mate from a different species.
Otherwise, genetic leaks would cause species boundaries to break down altogether. In some
closely related species there are recognized "hybrid zones".
For example, in Heliconius butterflies, hybrids are common, healthy and fertile - hybrids can
breed with other hybrids, or with either parent species. Genes have leaked from one species
into another through regular hybridisation. However, hybrids are disadvantaged by natural
selection. Pure-bred Heliconius butterflies have warning colouration recognised by predators.
http://messybeast.com/genetics/hybrid-mammals.html
Page 20
Hybrids have intermediate patterns which are not recognised - the predators have not yet
adapted and so the hybrids are disadvantaged. In mammals, hybrid White-Tail/Mule Deer
don't inherit either parent's escape strategy (White Deer dash. Mule Deer bound) and are
easier prey than the pure-bred parents.
Another example is seen in Galapagos Finches. Healthy Galapagos Finch hybrids are relatively
common, but their beaks are intermediate in shape and less efficient feeding tools than the
specialised beaks of the parental species so they lose out in the competition for food. Following
a major storm in 1983, changes to the local habitat meant new types of plant began to flourish
and the hybrids had a advantage over the birds with specialised beaks - demonstrating the
role of hybridization in exploiting new niches. If the change is permanent or is radical enough
that the parental species cannot survive, the hybrids become the dominant form. Otherwise,
the parental species will re-establish themselves when the environmental change is reversed
and hybrids will remain in the minority.
Finally, what happens if two species previously kept separate by geographical boundaries
suddenly meet up? The hybridisation of the native European Red Deer and the introduced
Chinese Sika Deer means that pure Red Deer are being hybridized into extinction. While
humans want to protect the Red Deer; evolution wants to utilise the Sika Deer genes.
Mechanisms for keeping species separate:Physical separation: the species live in different geographic locations or occupy different
ecological niches in the same location and so never have the chance to meet each other.
Temporal isolation: the species that mate during different seasons or different time of day and
cannot breed together.
Behavioral isolation: members of different species may meet each other, but do not mate
because neither performs the correct mating ritual. Imprinting by fostering the young of one
species on a female of the other species can overcome this in some cases.
Mechanical isolation: copulation may be impossible because of incompatible size and shape of
the reproductive organs.
Morphological isolation: copulation may be impossible because of the difference in body size or
shape.
Gametic isolation: the sperm and egg may not fuse and hence fertilization cannot occur; if it
does occur then the embryo fails to get past the first few cell division.
http://messybeast.com/genetics/hybrid-mammals.html
Page 21
HALDANE'S RULE
Haldane's Rule states that in animal species whose gender is determined by sex
chromosomes, when in the first cross offspring of two different animal species, one of the
sexes is absent, rare or sterile, that sex is the heterogametic sex. The "heterogametic sex" is
the one with two different sex chromosomes (e.g. X and Y); usually the male. The
"homogametic sex" has two copies of one type of sex chromosome (e.g. X and X) and is
usually the female.
Haldane's Rule for Hybrid Sterility states that a race of animals could diverge enough to be
considered separate species, but could still mate to produce healthy hybrid offspring in a
normal ratio of males and females. If any of the hybrid offspring were sterile, the sterile
offspring would be the heterogametic offspring (males). If the heterogametic offspring was
fertile, it produced the normal 50:50 ratio of X and Y sperm.
Haldane's Rule for Hybrid Inviability states that if the divergence between the species
became large enough to generate genic differences, but not to prevent mating, then parental
gene products may fail to co-operate during development of the embryo, resulting in hybrid
inviability (the hybrids are aborted, stillborn or don't survive to maturity). In this case, the
male to female ratio of hybrid offspring is skewed with more homogametic offspring while the
heterogametic offspring (males) are absent or rare.
Haldane considered the speciation process (i.e the "growing apart" of one species into two
species) to occur in stages. The first stage of the speciation process was complete if the two
species could mate and produce healthy but sterile hybrids. As the species continued to
diverge, they became genetically less compatible. These incompatibilities prevented hybrids
from being formed or caused them to die before maturity i.e. it didn't matter whether or not
they were sterile since they would not survive to breeding age. These are called "post-zygotic
barriers" because a zygote (fertilized egg) is formed, but the offspring (particularly the males)
do not breed.
As species differentiation progresses even further, it results in anatomical (body shape),
physiological (body function e.g. mismatched pregnancy periods) or psychological
(behavioural) differences which prevent the two species mating with each other. Haldane
called these "pre-zygotic barriers" because they prevent offspring from being conceived in the
first place.
Speciation can involve big jumps as well as gradual shifts and fertile hybrids are more common
than Haldane could have realised. The following examples show that some pre-zygotic barriers
can be overcome and that there are intermediate stages in post-zygotic barriers. The species
involved may have been kept separate by other means e.g. physical separation.
Male Jackals only mate with domestic bitches if the Jackal pups are raised by a domestic bitch
(to become imprinted on dogs). There is a psychological barrier, but the offspring are fertile
(pre-zygotic barrier, but no post-zygotic barrier). Lions and Tigers must overcome behavioural
(courtship) barriers, but produce fertile female offspring and sterile male offspring (pre-zygotic
and post-zygotic barriers). Lions and leopards have some physical barriers (size), but these
are overcome if the lioness lies on her side to let the leopard mount her; the male Leopons are
sterile, though female offspring are fertile (pre-zygotic and post-zygotic barriers). In these
cases, pre-zygotic barriers are overcome by rearing the two species together (in whales and
dolphins this occurs naturally).
Some cases seem to need additional rules! In Beefalo, Domestic cows may have an immune
response against Bison/Cow hybrid calves - this is a physiological barrier, but does not prevent
conception. Bison cows don't have this immune response against hybrid calves and hybrid
Beefalo males can be fertile. In some hybrids of domestic cats with small wildcats, a proportion
of hybrid males are claimed to be partially fertile (incomplete post-zygotic barrier?) and though
http://messybeast.com/genetics/hybrid-mammals.html
Page 22
the hybrid females are fertile they may not successfully raise their young - a psychological
barrier, but one which does not prevent mating/conception.
In addition to Haldane's Rules, the viability and fertility of hybrid offspring can depend on
which species is the male parent and which is the female parent since some embryo
developmental effects come into play depending on which genes come from which parent (e.g.
giantism in ligers, but not in tigons).
http://messybeast.com/genetics/hybrid-mammals.html
Page 23