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).


The black bear and the European brown bear were crossed 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 (considered by some to be a form of brown bear rather than a species) have been produced in Cologne.

American Black Bear (Ursus americanus) x Brown bear (U. arctos). Hybrids of both sexes are recorded and a hybrid was successfully backcrossed to a Brown Bear. A record size Black bear shot in Alaska was found to be a natural hybrid.


At Halle, starting in 1874 a series of successful matings of polar bears and brown bears were made. Examples of these hybrid bears were exhibited by the London Zoological Society. These hybrids proved to be fertile, both with one of the parent species and with one another (details below). Polar bear/Brown bear hybrids are white at birth but later turn blue-brown or yellow-white.

Crandall may have been unaware of the earlier Halle hybrids when he reported the first polar bear/brown bear cross as occurring at a small zoo in Stuttgart, Germany, where a female European brown bear (A. a. arctos) paired to a male polar bear gave birth to twin cubs in 1876. At least three further births were recorded, and the young were reported to have been fertile among themselves and when mated back to the parents or to animals of the same species as the parents. Full accounts of these experiments were given by Rong (1903) and Scherren (1907). Crandall noted that later interest was focused on the National Zoological Park where a female Alaskan brown bear (Ursus arctos gyas - William M Mann (1937)), mated with a polar bear and gave birth to three cubs in 1936. A second litter was born in 1939 to the same parents, although the female was then listed as middendorffi (Mann 1940). These cubs showed exceptional vigor and size, one male having reached a wieght of 1,160 pounds (Davis 1950). Two of the hybrid females were bred to a brother and produced several litters of cubs, of which some survived to maturity. A detailed account of these matings was given by Davis (loc. cit.) "

HYBRID BEARS (The Field, 30th June 1906) For some years past the pretty little zoological garden at Stuttgart has been noted for a race of hybrids between the Polar bear and the common brown bear of Europe. According to a recent Guide the founders of the race were a Polar bear purchased over thirty years ago and a brown bear born in the menagerie. The Polar bear was obtained by von Heuglin's expedition. These were put into a bear-pit In 1875, with the result that hybrids were produced, lighter in colour than the dam, but showing resemblance in shape to the sire as they grew up. One of the female hybrids was mated with the Polar bear in 1877 and had two white cubs, which unfortunately died in a few days, and the same result followed a similar birth In 1580. In December, 1881, there was another litter of two, of which one was killed by the dam. The survivor, a male, at a year old was quite white. Two hybrids bred at Stuttgart are now in the Zoological Gardens. One is a half-blood female, born in December 1893, and the other, a female, born in December, 1897, her cub by a Polar bear. The dam resembles a brown bear in colour, with lighter markings, and darker along the back and feet, intermediate in shape between the two species. The younger hybrid has nearly the form and colour of the Polar bear except for a light brown shade along the back. These animals have been placed in dens near the Polar bears, so that comparison between the parent species and the hybrids is rendered easy.

HYBRID BEARS (The Field, 27th April 1907) Hybrids between different species of rarely, if ever, occur in a state of nature, owing to limits of distribution, and their production in menageries is not often attempted, owing to the difficulty of keeping different species in one den. In some cases the difficulty has been got over by putting the animals together at an early age, the most successful instance being that of Herr Adolf of the Stuttgart Garden, who for nearly thirty years bred hybrids from a Polar sire and brown bear dam, the offspring being fertile inter se. The garden was closed and the stock sold last year, when the Hon. Waite Rothschild purchased and deposited in the Zoological Gardens the oldest two of these hybrids. At the scientific meeting of the society on Tuesday evening Mr Henry Scherren read a paper on the subject, giving a short account of the Stuttgart hybrids. Other cases mentioned are the birth of cubs in Regent’s Park in 1859, the dam being a European brown bear and the sire an American black bear. Cases of hybridity between the brown bear and the grizzly bear recorded in Der Zoologische Garten as having occurred in the gardens at Cologne and Hanover are referred to, but the author had ascertained, by the courtesy of the directors, that there was no official record of the births. The last case mentioned was that at Halle-an-der-Saale, where on Jan. 23, 1907, three cubs were born, the sire being a Polar bear and the dam a brown bear. The animals had been kept together for some years, and there seemed to be little doubt that this was the third lot of cubs, and that the other two were eaten by the dam. In the same garden Dr Brandes, the director, has had for more than a year a female Korean black bear in the same den with a pair of sloth bears. The animals agree very well, but so far there has been no signs of mating.

Clinton Hart Merriam, taxonomist 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") in 1918. The nearly full-grown female bear had been killed by 2 Inuit hunters in 1864 at Rendezvous Lake, Barren Grounds, Canada and its skull and enormous yellowish skin acquired by naturalist Robert MacFarlane (leading to its popular name of MacFarlane's Bear). MacFarlane shipped these to the Smithsonian Institute where they remained forgotten in a store-room until Merriam rediscovered them. Although MacFarlane's speciment was only belatedly recognised as unusual, the Inuit had, and still have, stories about strange-looking bears.

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 bear and relative of the modern spectacled bears. The oddly shaped skull and teeth differ from that of both the Grizzly and the Polar bear, indicating it is not merely a colour morph of either species (blonde brown bears are known and some captive Polar bears take on a yellowish hue). Today it is variously considered a natural hybrid between a grizzly bear and polar bear or an aberrant form of grizzly, although DNA studies and morphological analysis of the skull have not been carried out. A similar bear was reported from Kodiak Island. The confirmation, in 2006, of a hybrid occurring in the wild led to renewed interest in MacFarlane's specimen.

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 (a male hybrid successfully bred with his 2 sisters), indicating that the two species of bear are closely related.

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.

Instances of these hybrid bears reaching maturity and being fertile have been reported by (Kowalska 1969; Wurster-Hill & Bush, 1980). According to Zofia Kowalska (Scientific Assistant, Miejski Ogrod Zoologiczny w Lodzi, Lodz, Poland) in "A Note on Bear Hybrids: Thalarctos maritimus x Urus arctos", 4 sets of Polar bear x Brown bear hybrids were born at Lodz Zoo. The father was a Polar bear (Thalarctos maritimus) and the mother a Brown bear (Urus arctos).

This illustrates one aspect of Haldane's rule - the heterogamous sex (male in this case) being absent, rare or sterile; in this case more females were born and survived than males.

The parents had been housed together since 8 months old, were sexually mature at 64 months (5 years 4 months) and produced their first cubs at the age of 72 months (i.e. 6 years old). In the wild, male Polar bears do not reach sexual maturity until 8 years (Pederson, A, 1957; "Der Eisbär", Neue Brehm Büch. No 201: 1-64), but the Lodz Zoo's Polar bear impregnated the female when he was only 5 years old. Kowalska suggested the diet of captive Polar bears led to earlier sexual maturity.

Kowalska described the Lodz Zoo's hybris as all being much lighter in colour than the Brown bear while having the shape of the Polar bear. They all developed normally. A female hybrid from the 1961 litter mated with her Polar bear father in 1966 and on 20/12/1966 she produced a single male cub with nearly white fur. The other female from the 1961 litter was mated to a Brown bear in 1966 and on 19/12/1966 she produced 2 dark coloured male cubs, one having a light coloured head and neck. Kowalska submitted the report in June 1967 and it was published in 1969 continued to monitor these 2nd generation hybrids and was particularly interested in their fertility.

Hybrid of polar bear and brown bear at the Rothschild Zoological Museum.

Hybrid of polar bear and brown bear at the Rothschild Zoological Museum.

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. The second generation hybrids were brown with some white markings. 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.

Above is a one month old Polar/Grizzly hybrid cub, one of a number that bred by the Hawthorn Mellody Zoo. Later a Hawthorn act, which was presented by Eloise Berchtold in the midd-1970s had a couple of the hybrids in the act. They were quite a striking, beautiful animal. Large and thick like a Grizzly, with a light yellow/palomino colour coat.

Natural polar/grizzly hybrids have been dubbed "pizzly", "grolar" or "polargrizz" bears. The Canadian government suggested the name "Nanulak", taken from the Inuit Nanuk (polar bear) and Aklak (grizzly bear). Taxonomists suggest "Ursus maritimus horribilis", "Ursus maritimus x horribilis" or "Ursus hibrada maritimus horribilis". Where bear populations have been reduced or where human encroachment on habitat forces the two species into closer proximity, such hybrids appear to be becoming more common. Grizzly bears have been sighted in polar bear territory in the Western Arctic near the Beaufort Sea, Banks Island, Victoria Island and Melville Island. A "light chocolate colored" bear, possibly a hybrid (although Grizzly bears can have colour variants) was reportedly seen with polar bears near Kugluktuk in western Nunavut.

In 2006, on Banks Island, 2000 km north of Edmonton, Canada, a sports hunter from Idaho shot a male hybrid grizzly/polar bear. At first, Martell and his Inuit guides thought the animal was a polar bear, but closer inspection reveraled the features of a grizzly bear as well. The bear had thick, creamy white fur typical of a polar bear, but had the long claws, humped back and concave face of a grizzly bear. It's eyes were surrounded with rings of black fur and it had small brown patches of fur on its nose, back and one paw. The bear was one from a population at Sachs Harbour. The polar bear is a descendent of the grizzly bear (the grizzly is variable in colour and the palest bears would have had a survival advantage on the ice). A lab analysis of the DNA confirmed it was a hybrid. Analysis of mitochondrial DNA showed the mother to have been a polar bear and the father to have been a grizzly bear. With polar bears endangered, it is sad that $50,000 allows a trophy-hunter to kill one of these beasts. Other unusually coloured "polar" bears have been seen in the region and may also be hybrids. Polar bears normally give birth to two cubs and it is possible the shot hybrid has a sibling.

Inuvialuit hunter David Kuptana shot another hybrid on April 8th 2010 on sea after it scavenged through unoccupied cabins near Ulukhaktok (formerly Holman), NWT, on Victoria Island then approached the community. This is almost the same latitude and far from the mainland as the 2006 hybrid which was shot on adjacent Banks island. This second hybrid had creamy-white fur, typical of a polar bear, but had a larger head, long claws on the front feet and a ring of brown hair around its hind feet which suggested a grizzly bear. The head and ears had similarities to a grizzly bear. Wildlife DNA analysis showed it was a second-generation hybrid - the result of a female grizzly-polar hybrid mating with a male grizzly bear. This is the first time a second generation hybrid has been confirmed in the wild and means there is at least one female polar-grizzly hybrid near Banks Island. Further test will determine whether this bear was related to the male hybrid shot in 2006. The pelt was auctioned.

Polar/Grizzly bear hybrids will become increasingly common due to the absence of summer Arctic sea ice. Polar bears stranded on land will come into more contact with grizzly bears (or with other arctic brown bears such as the Kodiak or the Siberian Kamchatka bear). This has also allowed/caused interbreeding between harp seals and hooded seals and between beluga whales and narwhal. Interbreeding can be an evolutionary "shortcut" helping species adapt to major environmental changes. As well as speciation (divergence of one species into two or more), some related species can interbreed and converge. A cycle of divergence/convergence is found in Galapagos finches and is related to local environmental changes.

In October 2009, a detailed study of captive-bred Polar x Grizzly hybrids by Alexandra Preuß (University of Osnabruck), Dr Ute Magiera (Osnabruck Zoo) and colleagues was published in the scientific journal Der Zoologische Garten. With only one verified hybrid seen in the wild, the study looked at 2 captive-bred hybrids out of the 17 hybrids known to exist in captivity. A few hybrid bears exist in zoos in the Czech Republic, Israel, Russia, Spain, Poland and Germany as a result of grizzly bears (a subspecies of brown bear) and polar bears being housed together. A study of hybrids born at Osnabruck Zoo, Germany confirms some of the previous observations regarding colouration and structure of the feet. It noted that hybrids inherited some distinct characteristics from either parent and some characteristics that were intermediate.

At Osnabruck Zoo, Germany, a male polar bear and female brown bear had been housed together since 1980, but not produced any cubs. After 24 years together, in January 2004, the female brown bear gave birth to two brown/polar bear hybrids, much to the surprise of Dr Ute Magiera, the zoo's conservation coordinator. Soon after their birth, the two hybrids were moved to another zoo, preventing them from learning any behaviours from either parent. The male was sterilised, but the female may prove fertile. When adult, the hybrids were intermediate in size between the larger polar bear and the slightly smaller grizzly. They had the longer necks of polar bears, but small shoulder humps reminiscent of brown bears. The size and shape of their heads was intermediate between the thicker-set brown bear and the more slender-headed polar bear. They had visible tails, like polar bears (those of brown bears are almost invisible). The soles of their feet were partially covered in hair; polar bear feet are fully covered in insulating hair while brown bears have hairless soles with the toes clearly visible. A polar bear has hollow hair-shafts while the brown bear has solid hairs or hairs with small hollow regions. The hybrids' hair was intermediate having hollow pockets. The male hybrid had solid hair on its paws, but the dark hair on its back had hollow pockets. The female's hair had a range of hollow regions. Having been separated from their parents, the cubs were not able to learn any behaviours from them. Their innate behaviour was similar to that of the polar bear. They used their front legs to stamp on large toys, much as polar bears stamp on ice to break into seal dens. They used their teeth to fling jute bages from side to side, just as polar bears fling prey around. In contrast, brown bears did not show this behaviour when playing with similar bags. Like polar pears, the hybrids lay down on their stomachs with hind legs spraddled (like a frog) when resting.

Researchers have found that the female ancestor of all living polar bears was an Irish brown bear prior to the peak of the last ice age, 20,000 to 50,000 years ago. Beth Shapiro, the Shaffer Associate Professor of Biology at Penn State University and Daniel Bradley of Trinity College Dublin, published a study in the journal "Current Biology" in July 2011. Climate changes affecting the North Atlantic ice sheet probably gave rise to periodic overlaps in bear habitats resulting in interbreeding. Maternal DNA from brown bears entered the gene pool of polar bears. Although the two species are very different in terms of size, color, conformation, fur type, dentition, behaviour and preferred habitat, Shapiro stated "We know that the two species have interbred opportunistically and probably on many occasions during the last 100,000 years [...] previous research has indicated that the brown bear contributed genetic material to the polar bear's mitochondrial lineage - the maternal part of the genome, or the DNA that is passed exclusively from mothers to offspring. But, until now, it was unclear just when modern polar bears acquired their mitochondrial genome in its present form".


A hybrid between a Himalayan black bear and a North American black bear was supposedly born in the wild in the wild in Florida, after a Himalayan black bear escaped from a circus. According to Jack Hanna, author of "Monkeys on the Interstate" who helped wildlife officials capture the bear when it wandered into a residential area, "The bear was thought to be the offspring of a rare Himalayan sun bear [note: an error - Sun Bears are Malaysian] that had escaped from a circus several years back. He'd probably come down from the Ocala National Forest forty or fifty miles to the north, probably just walked right along the freeway. We released him back into the forest three weeks later. It was all tremendous publicity for the zoo.".


In 1975, within Venezuela's "Las Delicias" Zoo, a female black bear shared its enclosure with a spectacled bear, and produced several hybrid descendants.

Between 1963 and 1991, the "Las Delicias" Zoo exhibited a male Spectacled bear originating from a forest in the vicinity of Sanare, Lara State. Since 1964, this animal shared its enclosure with a female Asiatic black bear (Ursus thibetanus) originating from the Miami Zoo, U.S.A. This couple produced several descendants starting from 1975, when the first hybrid male cub was born.


In 2010, an Asian black bear/brown bear hybrid, rescued from a bile farm, was housed at the Animals Asia Foundation's China Moon Bear Rescue.


Although the geographic ranges of Ursus malayanus (Sun Bear) and the larger Ursus thibetanus (Asiatic Black Bear or Moon Bear) overlap extensively in mainland southeastern Asia, no natural hybrids have been reported. Both species occur in Cambodia and in 2005 an unusual looking male bear cub (dubbed specimen TM1) was rescued in forest along the O’Koki River in Preah Vihear Province of Cambodia. In 2007 it was housed at the Phnom Tamao Zoological Gardens and Wildlife Rescue Center, Takeo Province, Cambodia. TM1 was largely black and had a pale chest mark similar to that of an Asiatic Black Bear. Its mane and crest was like that of a Sun Bear (though some Asiatic Black Bears also have these). Its facial features were intermediate between those two species and the large canines resembled those of a Sun Bear. It resembled an Asian Black Bear with an unusually glossy coat and an unusual head. DNA analysis found that TM1 had a Sun Bear's mitochondrial DNA and its nuclear DNA was a mix of Sun Bear and Black Bear. This meant it was a hybrid between a male Black Bear and a female Sun Bear. There were no zoos or captive collections it could have escaped from, therefore it was a natural hybrid between the two species. At the Wildlife Recue Center, it was housed with Black Bears as it more closely resembled these.

Gary J. Galbreath , Matt Hunt, Tom Clements, and Lisette P. Waits - An apparent hybrid wild bear from Cambodia. Ursus 19(1):85–86 (2008)

A wild hybrid was reported in 2005. It was generally similar in appearance to the Sun bear, but the muzzle was similar to the Asiatic Black Bear. The ears and canine teeth were like those of the Sun bear. Its mitochondrial DNA was that of an Asiatic Black Bear hence it was a hybrid of male Sun Bear and Female Black Bear.


A sloth bear was hybridised with a Malayan sun bear at the Tama Zoo, Tokyo, and also with an Asiatic black bear (Selenarctos thibetanus) (Gray, 1972; Asakura, 1969; Scherren, 1907).

Sloth bear x Malayan sun bear hybrids were reported by Shigeharu Asakura (General Curator, Tama Zoological Park, Tokyo, Japan) in "A Note On A Bear Hybrid - Melursus ursinus x Helarctus malayanus - at tama Zoo, Tokyo) published in 1969. The zoo had kept a pair of Malayan sun bears (Helarctus malayanus) in the same enclosure as some Sloth bears (Melursus ursinus) since they were young. They were all on friendly terms with no aggression between the individuals of the 2 species. About 5 earlier, there had been occasional sexual behaviour between the Sloth bears, but they had not bred. The Malayan Sun bears had shown no signs of sexual behaviour at this time, except for occasional unsuccessful mounting behaviour by the male.

On 12/06/1966, keeper Yoshio Takura observed a male Sloth bear copulating with a female Malayan Sun bear. 95 days after the mating, on 14/09/1966, the female produced a single male cub. The hybrid came to resemble the Sloth bear father in terms of hair, body shape and colouration.


Sloth Bear (Melursus ursinus) x Brown bear (U. arctos) a hybrid was born at New York Zoo in 1916, but was destroyed in 1918 because it was so savage that its keepers could not enter the dens at cleaning time.

More information:

Asakura, S. 1969: A note on a bear hybrid, Melursus ursinus x Helarctos malayanus, at Tama Zoo, Tokyo. Int. Zoo Ybk. 9:88.
Gray, A.P. 1972: Mammalian Hybrids. A Check-list with Bibliography. 2nd edition.
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.]
Kowalska, Z. 1965. "Cross breeding between a female European brown bear and a male polar bear in Lodz Zoo." Przeglad Zoologiczny, 9:313-319. [Polish with English summary.]
Kowalska, Z. 1969. "A note on bear hybrids Thalarctos maritimus and Ursus arctos at Lodz zoo." International Zoo Yearbook, 9:89.
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.]
Martin, P.L. 1882. "On a hybrid between a male Ursus maritimus and a female Ursus arctos." Pederson, A, 1957; "Der Eisbär", Neue Brehm Büch. No 201: 1-64
Wurster-Hill, D.H. and Bush, M. 1980: The interrelationship of chromosome banding patterns in the giant panda (Ailuropoda melanoleuca), hybrid bear (Ursus middendorfi x Thalarctos maritimus), and other carnivores. Cytogenet. Cell Genet. 27:147-154.
Scherren, H.: Some notes on hybrid bears. Proc. Zool. Soc. London 431-435, 1907.
Alexandra Preuß, Udo Gansloßer, Günter Purschke and Ute Magiera. 2009: Bear-hybrids: behaviour and phenotype. Der Zoologische Garten Volume 78, Issue 4, 2009, Pages 204-220

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