Recreating extinct animals by selective breeding

By P.H.J. Maas / The Sixth Extinction

All of our domestic animals have wild ancestors. Our dogs originate from the wolf, our domestic pigs from wild boar, our domestic cattle breeds from the aurochs and our domestic horse breeds from the tarpan. All domestic breeds are created by selective breeding; people bred animals that had the characteristics that they wanted. The domesticated offspring's population surged, but some of their wild ancestors disappeared from the earth, such as the aurochs and the tarpan. The same has happened with some subpecies of surviving wild species. The quagga, a subspecies of the plains zebra, has been exterminated from the South African plains and the last captive individual died on 12 August 1883 in Amsterdam Zoo. The South African Quagga Project is attempting to recreate this remarkeble extinct subspecies by using surviving subspecies of the plains zebra in a selective breeding program. Another example is the Barbary lion, a North African subspecies of the lion that became extinct in the wild when the last known wild individual was killed in 1943 in Algeria. The former popularity of the Barbary lion as a zoo animal provides hope to ever see it again in the wild in North Africa. Especially the Moroccan royal lions and its descendants. These Moroccan royal lions and its decendants are now the focus of The Barbary Lion Project.

The selective breeding or back-breeding experiments of the Heck brothers are well known, but they are not the only back-breeding attempts. This article features the known selective breeding attempts that try to recreate lost ancestors of our domestic animals or lost subspecies of surviving wild species. Back-breeding is possible because much of the genetic material of the extinct wild ancestors and subspecies survived in the domestic progeny or in surviving related subspecies. This can result in animals that resemble the original extinct ancestor or an extinct subspecies. Back-breeding has an advantage over cloning in that it creates a whole population, rather than just an individual animal.Currently there are selective breeding programs for the extinct aurochs (Bos primigenius primigenius), tarpan (Equus ferus ferus), quagga (Equus quagga quagga) and the Barbary lion (Panthera leo leo).

 

Aurochs (Bos primigenius primigenius)

AurochsThe aurochs became extinct in 1627 and was much larger than the domesticated cattle breeds. The shoulder height of an aurochs bull probably varied between 160 and 180 cm, and that of an aurochs cow around 150 cm. The aurochs bull’s coat colour was black-brown with a small light eel stripe. The colour of the cow was just as the calves’ colour reddish brown. The bull as well as the cow probably had a light zone around the snout. The aurochs’ horns were pointed forward and were curved inwards. Although the shape of the horn was very characteristic for the aurochs, there was some variation in the length, thickness, curving, and position with regard to its forehead. The udder of the aurochs cow was small and hardly visible. (Van Vuure, 2003) Read more >>

Image: The Augsburg aurochs. This painting is a copy of the original that was present at a merchant in Augsburg in the 19th century. The original probably dates from the 16th century. It is not known if the original as well the copy still exist somewhere (Van Vuure, 2003). This image is in the public domain because its copyright has expired. This applies to the European Union, the United States, Australia and those countries with a copyright term of life of the author plus 70 years.

 

Heck Cattle

Heck CattleAlready in 1835, the Polish zoologist Jarocki pleaded in an article to undertake and attempt to get the aurochs back in its original form. But it lasted still almost hundred year before someone actively began with an attempt to re-breed the aurochs. The brothers Lutz and Heinz Heck have both made attempts to recreate the aurochs in Germany in the 1920s and 1930s. Both brothers did this through cross several cattle breeds, which possessed aurochs characteristics according to them, and to select the offspring. Each brother used his own selection of cattle breeds. Heinz began his experiment in the Hellabrunn Zoo in Munich. Lutz began a bit later than his brother with his experiment in Berlin. The result of their experiments to re-breed the aurochs was according to the Heck brothers quickly achieved and had a strong resemblance to the real aurochs. Lutz released his Heck cattle into the wild in large nature areas in Germany and Poland, but Heinz kept his Heck cattle exclusively in zoos and small game parks. Most likely the Heck cattle of Lutz have not survived World War II, and do only the Heck cattle of Heinz remain today. After the war, individual breeders have bred the Heck cattle to their own (often wrong) insight. Today, Heck cattle can be found in many places, like zoos and nature parks. (Van Vuure, 2003)

Image: Heck Cattle in nature reserve the Oostvaardersplassen in the Netherlands. Photographed by Gerard Meijssen on 16 September 2004. This image is licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license. A full resolution version can be found at Wikimedia Commons.

Relatively fast after the creation of Heck cattle there came criticism to as well the execution as the result of the re-breeding experiment. The criticism addressed especially on the image on how the aurochs looked like, that the brothers Heck had formed themselves. This image was created by a mixture of truth and mostly phantasy. There was even a difference of opinion between the brothers over how the aurochs looked like. Furthermore there was criticism on the way they bred and selected and on the speed on which they reached their end result. Heinz worked at most 12 years on his experiment, and Lutz only at most 11 years. The selection criteria were vague and broad, and there was no good administration kept of the crossings that had been made. The re-breeding experiment of Lutz and Heinz Heck is characterized by an incompetent and untransparent way of working.(Van Vuure, 2003)

When we now compare the Heck cattle and the real aurochs, we see that there is little similarity between the two. Only the colour of the fur of some Heck cattle is similar, but there are also many Heck cattle with a wrong fur colour. This is caused by the recessive genetic characteristics which still exist in Heck cattle and originated from the used domesticated European cattle breeds. Other characteristics, like the shape of the horns and body size, do not resemble the real aurochs. And the sexual dimorphism is almost gone in Heck cattle. The Heck brothers did not have all the information we have today, but for example the horn form was also known in their times. We don't even know everything about the aurochs today, e.g. the exact nuance in coat colour on each part of the body is not yet known and more research is necessary to determine the exact shoulder height. (Van Vuure, 2003)

A cattle population that as a whole has more characteristics of the aurochs than the current Heck cattle is that of the Spanish Fighting cattle. Within the heterogeneous population of the Spanish fighting cattle not only more aurochs characteristics are present, but often also combined in one individual. Within this populations there exist for example red-brown cows with a small utter and the aurochs horn shape, and black-brown bulls with a light eel stripe, a light snout and the aurochs horn shape. The selection and crossing of these Spanish bull fight can probably reach the target to recreate the aurochs much faster and better than has been done by the Heck brothers and their Heck cattle. (Van Vuure, 2003)

The Heck cattle of today can still be improved (Van Vuure, 2003). Since the 1990's a group led by Dr. Margret Bunzel-Drüke tries to improve the existing Heck Cattle breed in Germany in the area of Lippe (Soest, Westfalen). A group from Denmark is trying the same with 'Project Taurus'. The improvements are being made with the help of other cattle breeds, like Spanish fighting cattle (Toro de Lidia), Spanish Sayaguesa cattle and Italian Chianina cattle This might result in Heck cattle that really do resemble the Aurochs. (Van Vuure, 2003; Goderie & Kerkdijk, 2009)

TaurOs

Since, 2009, Stichting Taurus (Taurus Foundation), a private Dutch organization that uses feral cattle and horses in nature management and natural grazing schemes, is leading a selective breeding program in order to recreate the extinct aurochs through a combination of modern genetic expertise and old-fashioned breeding: The TaurOs Project. This recreated aurochs could help restore the European countryside in a more natural state, and replace the cattle breeds that are currently grazing in nature reserves in the Netherlands (Highland Cattle, Galloway Cattle, Deep Red Cattle and Heck Cattle) and eventually the rest of Europe. (Goderie & Kerkdijk, 2009; Faris, 2010)

Stichting Taurus' approach differs from former and current initiatives because the project has a broad scientific foundation with a multidisciplinary angle. The TaurOs Project includes multiple disciplines, like molecular biologists, geneticists, ecologists, archaeologists, archaeozoologists, historians, aurochs experts, cattle experts and European cattle breeding organizations. Scientists will recreate the aurochs' DNA from old bones and teeth fragments from museums. This DNA will be compared with that of modern European cattle to determine which breeds are genetically best suitable for this selective breeding program. (Goderie & Kerkdijk, 2009; Faris, 2010)

The basis for the TaurOs selective breeding program is the Highland Cattle, a Scottish breed. This breed has proven itself as a year round grazer in nature reserves. It has the ability to live independently in a (semi-)wild condition. Besides that, it's a community-minded animal which is, unlike for example Heck Cattle, not aggressive towards the public visiting nature reserves. In order to create a cattle breed that also resembles the aurochs in appearance, other cattle breeds are being used in this selective breeding program, namely the Maremmana 'primitivo' from Italy, the Podolica from Italy, the Pajuna from Spain and the Sayaguesa from Spain. At the end, Stichting Taurus want a new breed that resembles the aurochs, not only in phenotype, but also in genotype. (Goderie & Kerkdijk, 2009; Faris, 2010)

Diarmid Cattle

Diarmid CattleIn 1989, Michael McDermott began in Northome (Minnesota, USA) on his small family farm a breeding program in need to develop a very hardy commercial breeding cow. He soon discovered a far greater purpose for his cattle, filling the niche left by an extinct animal, the aurochs. Michael McDermott created Dairmid cattle, which are the result of artful breeding techniques combining the desirable traits of the Scottish Highlander, the Belgian Blue and the Angus cow. He claims that this three-way cross has the form and function of the aurochs and its genetics can be maintained from available beef breeds. His method and result might prove useful in the commercial beef industry, while also lending a hand to the very concept of sustainable forestry and agriculture.

Image: A blue Diarmid Cattle bull. Courtesy by Michael McDermott. All rights reserved.

They have produced thirteen colours, but does one ideally fit the extinct aurochs? According to Michael McDermott they have produced the basic black with red points. The majority of Diarmid cattle does not resemble the colour of the aurochs yet. Diarmid cattle are also smaller than the extinct aurochs. They are about 30 cm (one foot) taller than a Scottish Highland bull, but smaller than dairy bulls of Friesian and Brown Swiss. According to Michael McDermott, they do have a great deal of sexual dimorphism, the cows being smaller than their male counterparts. The skeleton has not yet been compared with aurochs remains. For the horn shape they rely on the Highland contribution, and found that the Belgian influence aids in producing the aurochs curve. like Heck cattle, the Diarmid Cattle does not resemble the aurochs completely, but it is certainly a very interesting attempt to re-create the extinct aurochs.

The breeding program ended in Kelliher in 2004, when they had to sell the majority of their animals. However their efforts continue. Their next breeding experiment will begin with the Breed Bazadaise on Highland Cattle.

 

Tarpan (Equus ferus ferus)

Tarpan Supposedly, the last tarpan in the wild, a mare, died in the Tavrichesk steppe 35 km from Askaniya Nova in the Ukraine in December 1879 (Bennett & Hoffmann 1999; Day 1981; Suffolk Wildlife Trust 2009). It fell down a crevasse, while attempting to avoid capture (Suffolk Wildlife Trust 2009). It is claimed that the last tarpan went extinct in Poland in 1918 or 1919 (Kavar and Dovč 2008), apparently captive-bred animals were maintained on stud farms until that time (Bennett & Hoffmann 1999; Heptner et al. 1961). The tarpan was about 130 cm high at the withers. It was mouse-grey in colour, with a well-developed black mid-dorsal stripe, partly falling mane, and a slightly concave facial profile. (Bennett & Hoffmann, 1999) Read more >>

Image: As far as I know there exist only one photo of a live tarpan. This tarpan stallion was caught in 1866 and purchases by the zoo of Moscow, Russia. There is some doubt if this was a pure tarpan. It had remarkably long manes. This animals is known as the "Tarpan of Kherson", named after the area it was caught. According to its description it was dark mice grey coloured with black legs. It had also a dorsal stripe and weak striping on the forelegs. Its tail was cut by keepers. This tarpan died aged 21. This image is in the public domain because its copyright has expired. This applies to the European Union, Canada, the United States and those countries with a copyright term of life of the author plus 70 years.

 

Heck Horse

Heck HorsesThe German zoologist and Director of the Berlin Zoo, professor Lutz Heck, and Heinz Heck who was working at the Tierpark Hellabrunn (Munich Zoo), started in the early 1930’s a selective breeding programme in the hope of bringing back the extinct tarpan. They believed that all living creatures were the result of their genetic make-up and that genes could be rearranged like the pieces of a puzzle to recreate certain vanished species. Only breeds that still had living descendants could be recreated because those living breeds would be a source for genetic material. Several European pony breeds had descended from the Tarpan. Primarily the Heck Brothers selected Polish Koniks, Icelandic Ponies, Swedish Gotlands and Polish Primitive Horses from the preserve in Bialowieza. Mares from these breeds were then mated to Przewalski stallions because the Heck brothers felt that the blood of the wild Przewalski would serve as a catalyst to draw out the latent Tarpan characteristics dormant in these more modern breeds. At first the Przewalski horse influence was too strong, but by 1960’s he succeeded to produce a horse, which resembled the skeletal evidence of the extinct Tarpan in the archives of Munich Zoo. The first bred back "Tarpan" or Heck Horse, a colt, was born May 22, 1933 at the Tierpark Hellabrunn in Munich, Germany. These horses still survive as Heck Horses.

Image: Two Heck horses in the zoo of Stadt Haag, Austria. Photographed by Christian Jansky on 29 March 2007. This image is licensed under the Creative Commons Attribution-Share Alike 2.5 Generic license. A full resolution version can be found at Wikimedia Commons.

Konik Horse

Konik HorsesIn 1936, professor Tadeusz Vetulani of Poznan University also began attempts to breed the Tarpan back to its original state. The Polish government commandeered all the Koniks, which displayed Tarpan-like features. Two of the horses, a stallion called “Tref” and a mare called “Czajka”, even turned white in winter, but face, fetlocks, mane and tail retained the dark colour, which the extinct Tarpan also did. After 3 years there were 18 horses at Bialowieza, 8 having been born in the Bialowieza forest. Another reserve was established in the Popielno forest. The result of this selective breeding programme is that semi-wild herd of modern "Tarpans" or Konik Horses can be seen today. Many of these Konik Horses can be found in nature reserves and parks in Europe.

The recreated Konik Horse and Heck Horse are strong horses. It is resistant to harshness of climate, a prolific breeder that rarely aborts, great fertility, a strong immune system, its wound heals without attention, it is used to foraging in the wild, and can live on next to nothing. However these recreations; resembles the original extinct Tarpan in its skeleton, colour type, there is no genetic evidence that these modern "Tarpans" are really the same as the original extinct Tarpan. One characteristic of the true Tarpan that as well the Heck brothers as professor Vetulai did not succeed in recreating are the upright manes.

Image: Konik Horses in nature reserve the Oostvaardersplassen in the Netherlands. Photographed by Gerard Meijssen on 16 September 2004. This image is licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license. A full resolution version can be found at Wikimedia Commons.

Hegardt or Stroebel's Horse

In the mid-1960s, Harry Hegardt started in Redmond (Oregon, USA) a selective breeding project dedicated to recreate the extinct Tarpan from diluted genes still found in North American feral mustangs herds and in working horses on local ranches. He started to get the right colour, the right size and then he even started getting the stand-up mane. Harry Hegardt died in 1990. His herd of 20 horses were bought by Lenette and Gordon Stroebel who continued his project on their ranch in Prineville (Oregon, USA). They eventually named their ranch Genesis Equines. Like Hegardt, the Stroebels believe that strong Tarpan genes lie hidden in the wild mustang herds. That’s because those mustangs are descendants of horses that escaped from Spanish conquistadors in the 1500s. It is assumed that the Spanish conquistadors took some horses with Sorraia (a primitive Iberian horse breed probably closely related to the Tarpan) origins to the Americas, as there has been mtDNA evidence that has found Sorraian gentotypes in a couple of feral horse groups of western USA. The Stroebels capture horses from the wild, animals with characteristics of the extinct Tarpan, and breed them to draw out these characteristics. The future of the herd is uncertain, depending on whether or not a suitable source of new genetic material is found, but the Stroebels are hopeful and proud of their little herd of unique horses.(Flaccus 2002; Richins 2006)

 

Quagga (Equus quagga quagga)

Quagga in London ZooThe last free Quaggas may have been caught in 1870. Possible, a small population survived south of the Vaal river until about 1878, when there was a period of severe drought. The last captive Quagga, a mare, died on 12 August 1883 in Amsterdam Zoo, where she had lived since 9 May 1867. It was not realised that this Quagga mare was the very last of her kind. Because of the confusion caused by the indiscriminate use of the term "Quagga" for any zebra, the true Quagga was hunted to extinction without this being realised until many years later. The Quagga was a southern subspecies of the plain zebra with withers of 1.30 meter. It differed from other zebras mainly in having been striped on the head, neck, and front portion of its body only, and having been brownish, rather than white, in its upper parts. (Maas, 2008) Read more >>

Image: The only Quagga to ever have been photographed alive was the Regent's Park Zoo mare in London. Five photographs are known, taken by Frederick York and Frank Haes in 1870. This image is in the public domain because its copyright has expired. This applies to the United States, Canada, the European Union and those countries with a copyright term of life of the author plus 70 years.

 

Quagga ProjectIn 1971, Reinhold Rau visited museums in Europe to examine most of the preserved Quagga specimens, after having dismantled and re-mounted the Quagga foal at the South African Museum in Cape Town in 1969/70. During this tour he discussed the feasibility of attempting to re-breed the Quagga with Dr. Th. Haltenorth, mammalogist, at Munich, Germany. Dr. Haltenorth saw merits in such a plan and expressed his surprise that such a programme had not already been started in South Africa.

Image: the most quagga-like foal to date, born 20 January 2005. This young colt "Henry" was born on 20 January 2005 and is the third generation offspring from the mother's side, while only second generation from the father's side. Photographed by March Turnbull. Courtesy by Reinhold Rau / The Quagga Project. All right reserved.

Having critically examined twenty one of the twenty three preserved Quaggas, and being familiar with the high degree of variation in the plains zebra (Equus quagga) populations inhabiting the Etosha National Park in Namibia, the Kruger National Park, as well as parks in Zululand and Swaziland, Rau decided to work towards the implementation of a Quagga re-breeding programme. Contact was made in 1975 with zoologists and Park authorities, in the hope of stimulating interest in the project. Reactions to his proposals were on the whole negative, which was not surprising, considering that most English language scientific literature considered the Quagga as a separate species, a view, if correct, would render any attempt to re-breed the Quagga a futile exercise. However, Rau did not abandon his re-breeding proposal, as he considered the Quagga to be a subspecies of the plains zebra. The plan received new impetus in the 1980's by molecular studies that compared sequences of genetic code of Mitochondrial DNA extracted from tissue samples from a Quagga's skin. Comparison of these sequences with those of the plains zebra, demonstrated their close affinity, at least with reference to the sequenced genes, indicating that the Quagga was a subspecies of the plains zebra. 

Then came another fortunate event. The retired veterinarian, Dr. J. F. Warning of Somerset West, contacted Rau during the latter part of 1985. He was an expert in animal husbandry and had been associated in horse and cattle breeding for more than 50 years in Germany and Namibia. He was a friend of Prof. Lutz Heck and had spent much time with him during the latter's stay in Namibia. Gradually a more positive attitude was taken towards the proposed Quagga re-breeding programme, as the DNA examination results appeared in publications from 1984 onward. Influential persons became involved and during March 1986 the project committee was formed. During March 1987 nine zebras, out of approximately two thousand five hundred, were selected and captured at the Etosha National Park. Their capture and arrival at the specially constructed breeding camp complex at the Nature Conservation farm 'Vrolijkheid', near Robertson, in the Cape, on 24th April 1987, marked the start of the Quagga re-breeding project.

An important mile-stone in the 13 year history of the Quagga Project has been reached on the 29th June 2000. The Quagga Project Association, represented by its chairman Dr Mike Cluver and South African National Parks by its CEO Mavuso Msimang have signed a co-operation agreement. While active co-operation between the two bodies started with the translocation of the 14 Quagga Project zebras into the Karoo National Park during 1998, the now signed agreement changes the Quagga Project from a private initiative to an officially recognised and logistically supported project.

The selected plain zebra's had some Quagga characteristics, such as a brownish basic colour, much reduced striping, white tail-bush, etc. The aim of the Quagga project is to attempt to breed through selection a population of plains zebras, which in its external appearance, and possibly genetically as well, will be closer, if not identical to the former population known as 'Quagga'. The photo made by March Turnbull These new 'Quaggas' will be reintroduced into reserves in its former habitat. For more information about this project, see www.quaggaproject.org.

Quagga Project Donation

 

Barbary Lion (Panthera leo leo)

Barbary Lion in AlgeriaBarbary lions have a greyish pelage, longer fur creating a shaggy look, females and young males possessing long hairs around neck/throat, back of front legs and along belly, males possessing a huge mane covering not only head, neck and shoulders, but also extending behind shoulders and covering belly, colour of the mane varying amongst the parts of the body and becoming darker towards the posterior parts, well-developed tail tuft, higher occiput (back of head), with a more pointed crown, creating a straighter line between the tip of the nose and the back of the head, rounded cheek and proportionally narrow muzzle, and narrow postorbital constriction of the skull (Leyhausen, 1975; Hemmer, 1978). It is believed that Barbary lions possess the same belly fold (hidden under all that mane) that appears in the Asian lions (Panthera leo persica) today. It is the largest of the lion subspecies with males weighing between 230 to 270 kg and females 140 to 160 kg. (Yamaguchi and Haddane, 2002). Read more >>

Image: A wild Barbary lion in Algeria. Photographed by Sir Alfred Edward Pease around 1893. This image is in the public domain because its copyright has expired. This applies to the European Union, Canada, the United States and those countries with a copyright term of life of the author plus 70 years.

 

Possible Barbary Lion SamiraThe former popularity of the Barbary Lion as a zoo animal provides the only hope to ever see it again in the wild in North Africa.

Image: Samira, a possible Barbary lion or descendant from Port Lympne Animal Park in Kent (England, United Kingdom). She was born on 10 July 2003. This photograph was uploaded to the English Wikipedia in 2007 by an user named 'Barbary Lion', although it was probably created in 2005. It was later transferred to Wikimedia Commons. This work has been released into the public domain by its author, 'Barbary Lion, at the wikipedia project. This applies worldwide.

Even before Rabat Zoo was created, a German naturalist, Wolfgang Frey, who had been intensively searching for information on the Barbary lion, clearly pointed out the importance of the Moroccan royal lions. Realising how precious this bloodline was, Yves Raymond, then Director of Rabat Zoo, started to make contact with zoologists worldwide. Among them were the renowned big-cat experts Professors Helmut Hemmer and Paul Leyhausen. After being unable to answer all questions about the genetic purity of these royal lions, the zoologists decided to move forward by assuming that gene contaminations) had happened. A selective breeding programme was proposed. (Yamaguchi and Haddane, 2002)

In association with Oxford University, an UK-based organisation, Wildlink International launched their ambitious Atlas Lion Project. Wildlink International aimed to identify the Barbary markers by testing the skeletal remains of known Barbary lions in museums and collections around the world, including Barbary bones from the Coliseum in Rome. WildLink International disappeared after a while. In June 2009, the website The Sixth Extinction received new information from Wildlink International. This resurrected non-profit organisation from Aldington (Kent, England, United Kingdom) builds directly on the work of the former WildLink International. An urgent scientific population assessment of Panthera leo leo is being conducted by Pete Thompson of Wildlink International in association with Professor Helmut Hemmer (IUCN Cat Specialist Group Member) and Dr Joachim Burger of the University of Mainz (Rhineland-Palatinate, Germany). The priority now is to complete the Urgent Population Assessment without further delay (Tefera, 2003; Burger and Hemmer, 2006, Yamaguchi, 2006). (Lauren, L., personal communication 2009; WildLink International, 2001)

Meanwhile, Simon Black, of the Durrell Institute of Conservation and Ecology at the University of Kent in Canterbury (United Kingdom), and colleagues Nobuyuki Yamaguchi, Adrian Harland and Jim Groombridge have created a Barbary lion stud book. This studbook identifies the surviving individuals, their locations, their interrelatedness and their line of descent from the original Moroccan royal population. (Black et al., 2009; Walker, 2009) The current known captive Moroccan royal lion groups in Spain, Germany, UK, France, Morocco, Czech Republic, Austria and Israel are sourced from four zoo-based family lineages: Rabat, Olomouc, Washington and Madrid (Black et al. 2009). When genetically proven similar to the Moroccan royal lions, other zoo lions could be included in future breeding efforts (Black et al. 2009).

The results will be used to develop a scientifically justified conservation breeding programme that best meets the criteria of the International Union for the Conservation of Nature (IUCN). As a final goal, reintroduction within IUCN guidelines is planned as soon as possible in the Host Country of Morocco.( Lauren, L., personal communication 2010)

 

References

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Black, S., Yamaguchi, N., Harland A. and Groombridge J. (2009). Maintaining the genetic health of putative Barbary lions in captivity: an analysis of Moroccan Royal Lions. European Journal of Wildlife Research.

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Citation: Maas, P.H.J. (2011). Recreating extinct animals by selective Breeding. In: TSEW (). The Sixth Extinction Website. <http://www.petermaas.nl/extinct>. Downloaded on .
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