Let's Make a Mammoth
Evolution assumes that extinction is forever. Maybe not. Henry Nicholls asks what it would take to bring the woolly mammoth back from the dead (Nature).

Imagine never having to worry about a species going extinct again. What if we could store and preserve the genomes of modern species that are threatened or endangered? In fact, this is already being done. The Frozen Ark Project, among others, are preparing to collect samples of the world's most threatened species. This is all done in the hopes that we could resurrect these unfortunate species if they ever went extinct.

Notwithstanding the straightforward approach of this idea, many still find ethical reasons to oppose this scheme. Some environmentalists argue that the Frozen Ark and similar efforts could result in public indifference; if we can just resurrect them later, why worry about a species going extinct? It is true we would do well to focus more energy of conservation. What do you think?

Taking this idea much further, we have several samples of intact tissues from recently extinct species, such as the woolly mammoth, thylacine (Tasmanian tiger), and the dodo. So far, the Pyrenean Ibex is the only extinct animal to have been resurrected through cloning technology.

WOOLLY MAMMOTH

With the exception of dinosaurs, few extinct animals stir the imagination like the Woolly Mammoth. These elephant-like giants roamed much of North America, northern Eurasia, and Siberia. They were well adapted to cold weather, especially having their characteristic thick shaggy fur. Mammoths likely went extinct due to habitat loss during the ice melting at the end of the Ice Age. Human hunting may have finished off the remaining populations. Some subspecies of mammoth lived as recently as about 4,000 years ago, but their golden age was the Pleistocene.

Woolly Mammoths may offer the greatest potential for the resurrection of a prehistoric creature. This is because, unlike most fossil remains, mammoth carcasses are sometimes preserved in ice and permafrost. Several intact specimens have been discovered in past decades, most recently the unearthing of a female calf named Lyuba, about 40,000 years old. Like many well preserved mammoths, she was found in Siberia, and taken to the Russian Academy of Science's Zoological Institute to better preserve the body.

DNA in these frozen mammoth carcasses is in very good condition, but the freezing process probably destroyed any existing cells. Stephan Schuster and Webb Miller (Penn State University) reportedly sequenced half of the mammoth genome. The complete mitochondrial DNA (mDNA) profile of the mammoth had already been sequenced, revealing its close relationship to modern elephants, from which it diverged about 6 millions years ago, about the same time as the divergence of chimpanzees and humans. Some scientists are looking for preserved mammoth sperm cells that could be used to fertilize the egg of a modern Indian elephant, producing a hybrid. Even in the absence of cells, the intact DNA may still be useful and could be injected into the vacated egg of an elephant in order to produce a mammoth clone. In early 2011 a Japanese team announced their intention to have a baby mammoth within 6 years. This mammoth would be placed in Pleistocene Park, an development currently underway in northeastern Siberia. The goal is to reestablish the Ice Age environment, including all the flora and fauna from that period.

PYRENEAN IBEX

The causes for the recent extinction of the Pyrenean Ibex is unknown, but there are several theories including an inability to compete for food in its local mountainous habitat in Spain. The last ibex, also known as a bucardo, was killed by a fallen tree, discovered in 2000. Her name was Celia

Among recently extinct species, it is of great interest because it was the first extinct species to be cloned and successfully resurrected, albeit briefly. Celia's body provided plenty of intact tissue. Somatic cells from Celia's body were placed in the vacated oocyte of a goat and likewise gestated in the womb of a surrogate goat. In 2009 a baby Pyrenean Ibex was born, but died 7 minutes later due to lung defects. However, the team of Spanish and French scientists has not given up and is continuing its attempts to resurrect the extinct ibex.

The cloning of the Pyrenean Ibex presents an interesting case study in modern biotechnology. Specifically the single clone would not be enough to reestablish an ibex population. This is because the clone would be female and so there would be no male to breed with. It may be possible to breed a female clone with a male subspecies, but the resulting offspring would be hybrids and not true Pyrenean Ibex. With future improvements in biotechnology, scientists may be able to replace one of the female clone's X chromosomes with a Y chromosome from another subspecies, creating a male ibex.

DODO

Dodos, familiar to most of us, have been characterized as being clumsy and slow birds that weren't exactly playing with a full deck of cards. They were also flightless. These descriptions, if accurate, may indicate why the dodo was so easily hunted to extinction, or else destroyed by exotic introduced species due to its fearlessness. It was most closely related to pigeons, a group of animals that has, in contrast, found incredible success living alongside humans.

There is little to no available tissue remaining for the purpose of cloning. The last known stuffed specimen was held in the Oxford Ashmolean Museum, but was ordered to be discarded in the mid-1700's. Any remains of that specimen are likely very degraded or totally gone. Nonetheless, a discovery in 2007 of a complete dodo skeleton allowed for the extraction of DNA that made it possible to compare the dodo's DNA to modern birds, which is how we know it's so closely related to pigeons.

THYLACINE

The Thylacine, AKA Tasmanian Tiger, was a marsupial that lived in mainland Australia and Tasmania. It was hunted vigorously by European settlers, though, by that point thylacine populations were already dwindling or absent from mainland Australia. Like other marsupials, thylacines had pouches, interestingly in both sexes. Thylacines have been around for about 4 million years and their family stretches back to the Miocene.

In the last days of its species, there were thylacines at the Hobart Zoo in Tasmania as well as the London Zoo, but they all died in captivity. In 1999 the Australian Museum in Sydney began a project to extract DNA from stuffed specimens in an attempt to clone the thylacine. While that project was canceled due to overly degraded DNA (although it could be replicated), some academics at the University of New South Wales and other locations continue the effort.

1933 video footage of the last thylacine in captivity prior to its extinction

Museum of Natural History at Tring

Image of Henry, the modern-day quagga foal produced by the Quagga Project, using selective back breeding.

QUAGGA

The Quagga is a subspecies of the well-known Plain Zebra, presenting the apparent hide pattern in that its rear half is brown rather than striped. It used to be common in South Africa until it was hunted to extinction for its leathery hide and meat. The last wild quagga was killed in 1870 and the last one living in captivity died in 1883 at the Natura Artis Magistra Zoo in Amsterdam.

The quagga was the first extinct species to undergo DNA analysis. The Smithsonian Institution found that quaggas were in fact a subspecies of zebra rather than a distinct species. Currently the Quagga Project, founded by Reinhold Rau, is attempting to selectively breed modern zebras to realize the return of quaggas. The project has had some success - the fourth generation quagga foal, named Henry, appears superficially very much like the extinct quagga. There is a relatively large source of quagga DNA available, with many quagga skins and 23 known stuffed specimens in various museums around the world.

PASSENGER PIGEON

Passenger Pigeons used to be extremely common in North America and were known to form gigantic flocks, even as large as a mile wide. They came under threat during the 19th century when they were used for cheap meat for slaves. The last passenger pigeon was named Martha and died at the Cincinatti Zoo in 1914. Martha was stuffed and is kept in the Smithsonian Museum archives.

Prior to Martha's death, some laws had been established in an attempt to conserve the species. Some breeders attempted to reintroduce the populations into the wild or breed the pigeons in captivity, but all of these efforts failed because of the behavioral aspects of the passenger pigeon, which required large colonies to properly breed.

In 2010 the passenger pigeon's DNA (there are many skins and preserved specimens, including bones) was analazyed and it was found that it is most closely related to American pigeons. Some believe that the passenger pigeon could be cloned by inserting recovered DNA into the egg of a modern pigeon or mourning dove.

GOLDEN TOAD

In 1966, herpetologist Jay Savage discovered the Golden Toad. He stated, "I must confess that my initial response when I saw them was one of disbelief and suspicion that someone had dipped the examples in enamel paint." The toads were found in the Mountverde Cloud Forest Preserve in Costa Rica, but have not been seen since 1989.

Unlike many recently extinct species, golden toads likely died out primarily due to natural causes. 1987's weather patterns dried up much of the local larval pools, resulting in their deaths. There was also a fungus at the time that targeted golden toads and probably dealt an additional blow to the toads, already suffering from the drought.

CARIBBEAN MONK SEAL

Caribbean Monk Seals were the only seals native to the Caribbean Sea and the Gulf of Mexico. Their extinction was the direct result of humans hunting them for food and oil, as well as outright slaughtering by fishermen who viewed them as competition for fish. Christopher Columbus, during his 1494 voyage, called the seal a "sea-wolf" and eight of them were killed by his crew.

Like the Dodo, the monk seal was friendly and unafraid of humans, and likewise this behavior probably contributed to its extinction. Even though the last sighting was in 1952, the Caribbean Monk Seal was not declared extinct until 2008. Reports of sightings continue today, but have not been confirmed.

BUBAL HARTEBEEST

The Bubal Hartebeest went extinct in 1923 when the last living specimen died in captivity at the Paris Zoo. In the ancient world it was domesticated by the Egyptians and may have been used as a sacrificial animal. Europeans hunted the hartebeest for meat and recreation. The last one to be shot in the wild was found in Algeria in 1902.

These animals were receptive to captive breeding and so conservation breeding and reintroduction efforts likely would have succeeded, but that option was not considered until after the hartebeest's extinction. It has been proposed that the related Western Hartebeest should be introduced into the Bubal Hartebeest's previous living space in order to restore the local ecology.

JAVAN TIGER

As the name implies, the Javan Tiger was a subspecies of tiger isolated to the Indonesian island of Java. These tigers were smaller than those on the Asian mainland, probably because of island lifestyle and associated food limitations. At one time they were abundant and considered to be pest, but as human populations increased in Java, the tiger's habitat was fragmented and cleared for crops like rice and coffee. Adding insult to injury, the locals deliberately poisoned the tigers during this process.

In 1971 the last confirmed tiger was shot in southeast Java. Several biological searches, several making use of infrared cameras, were unable to get a single tiger photo. As a result the tigers were declared extinct in 1994. In 1999 the Canadian Tiger Foundation and the Sumatran Tiger Project set up a series of infrared cameras and observed the area for a year, but likewise found no tigers. The photographs revealed scarce prey and many poachers.

Despite continuing visual reports of the Javan tiger, DNA analysis of fecal matter found in Java has failed to confirm its existence. Most likely the reports come from leopard sightings. There have been no attempts to resurrect the Javan tiger, but there are available sources of DNA, including tiger hides kept in private collections.

BAIJI (CHINESE RIVER DOLPHIN)

The Baiji, or Chinese River Dolphin, was a unique-looking dolphin with a pronounced snout. Prior to the 1970s, Baiji were common in the Yangtze River, but fishing and water pollution (industrial and residential) nearly destroyed the animals. In the 1970s and 1980s, about half of Baiji deaths were a result of entanglement in fishing nets. By the end of that decade, only a few hundred were left.

In 1997 a thorough search indicated there were only 13 dolphins remaining alive in the wild, but a 2006 expedition failed to sight any Baiji. As a result of the 2006 expedition, the Baiji was declared functionally extinct, though it may just be critically endangered. Conservation scientists felt an ex-situ solution would be best and have concluded that the Shishou Lake might provide a new home for the Baiji, but the only Baiji transferred there died. In 1992 the Wuhan Institute of Hydrobiology created a Baiji dolphinarium to provide an artificial zoo-like home for the Baiji, but it remains unused for this purpose and is instead setup for the preservation of Yangtze finless porpoise.