Cloning of extinct or endangered species
Cloning of extinct or endangered species is an emerging scientific endeavor aimed at preserving biodiversity and preventing the loss of species due to extinction. As human activities continue to threaten animal habitats and contribute to a significant increase in extinction rates, researchers are exploring advanced reproductive biotechnologies, particularly cloning, as a potential solution. The process involves techniques such as interspecies nuclear transfer, where genetic material from an endangered species is inserted into the egg cell of a closely related species, allowing for the possibility of creating cloned animals.
Notable attempts at cloning have resulted in some successes, including the cloning of bantengs and the black-footed ferret, using preserved genetic material from "frozen zoos". However, the process is complex, with low success rates and ethical debates surrounding the potential ramifications for genetic diversity and ecosystem health. Critics argue that cloning may not address the underlying issues that lead to a species' endangerment, such as habitat loss. Thus, while cloning offers a glimmer of hope for species revival, it raises important questions about the long-term survival of species in their natural habitats and the need for comprehensive conservation strategies.
Cloning of extinct or endangered species
The threat of extinction to endangered animal species is of great concern to conservation biologists and animal lovers everywhere. Extinction is the dying off of all members of a species. When it occurs naturally, as part of evolution in response to global climatic changes and dynamic relationships within ecosystems that result in interspecies competition, the process is termed background extinction.
Conservation biologists have noted that ever since the 1600s, the rate of animal species extinction has increased significantly, primarily due to the rapid growth of the human population and the resulting destruction of animal habitats as well as human activities contributing to global warming. Conservation biologists have theorized that the planet is in the midst of the greatest period of animal extinction since the dinosaurs disappeared sixty-six million years ago. Such wide-scale extinctions may have profound effects on ecosystem survival as they culminate in the irretrievable loss of thousands of species of plants and animals, some of which have never even been identified. Some of extinctions of note include the great auk and the passenger pigeon, both of which disappeared in the nineteenth and early twentieth centuries. Other species, such as the California condor, are on the verge of extinction. Mammals are not exempt from this list; in 2024, the International Union for Conservation of Nature (IUCN) considered 26 percent of the world's mammals to be in danger of extinction. This threat of extinction affects ecosystem diversity.
Due to modern advances in reproductive biotechnology, however, the rise and decline of a species may no longer be determined solely by the forces of natural selection and the survival of the fittest, as proclaimed by evolutionary biologist Charles Darwin. Rather, the tools of recombinant DNA technology may afford humans a role in preventing the extinction of endangered species. On this rapidly evolving planet, where human civilization increasingly encroaches on the domain of the natural world, the possibility of preserving endangered wildlife species via biotechnology may be the last remaining hope for treasured animal species whose numbers have dwindled or disappeared entirely. The scientific name for the technologies that enable reversing extinction is known as resurrection biology or species revivalism.
Cloning Technology
The basic scientific procedure that has made this hope possible is a cloning technology termed nuclear transfer. The most effective form of nuclear transfer, known as the Honolulu technique, involves inserting the nucleus of a somatic (body) cell from an endangered animal into an egg cell obtained from a closely related species. First, the nucleus of the endangered animal's somatic cell is removed, as is the nucleus of the egg cell. These nuclei contain the genetic material of the animals they came from. Then the nucleus of the somatic cell is inserted into the egg cell by a microinjection technique using a fine needle. The egg cell is then placed in a chemical bath to stimulate cell division. An earlier alternative method is the Roslin technique, in which the nucleus is not removed from the somatic cell; rather, the cell is starved of nutrients, so it becomes dormant, then placed next to an egg cell from which the nucleus has been removed. An electric pulse fuses the somatic cell with the egg cell, the nucleus enters the egg cell cytoplasm, and cell division begins.
The genetic material of a fully differentiated or mature somatic cell, such as a skin cell, becomes genetically reprogrammed once inserted into the egg cell to generate all the cells that will ultimately make up the tissues and organ systems of the fetus. Because the somatic cell and the egg cell originate from two different species, the procedure is termed interspecies nuclear transfer. This concept is critical to cloning endangered species since it is often impossible to harvest egg cells from the threatened species, so a related but thriving species must serve as the egg donor. Once the nuclear transfer has been accomplished, the embryonic cells are implanted into the uterus of a surrogate mother, also from a related species. The result is that an animal of one species participates in reproducing a cloned animal of a different species.
Scientific Advances
The world’s first successful cloning of an animal belonging to an endangered species by interspecies nuclear transfer was carried out by researchers at Advanced Cell Technology (ACT) in Worcester, Massachusetts, who cloned a baby gaur, an oxlike animal found in India, Indochina, and Southeast Asia. Using skin cells from the gaur as a source of genetic material, internuclear transfer by microinjection of an egg cell obtained from a cow and subsequent implantation into the uterus of a cow serving as a surrogate mother resulted in the birth of a cloned ox named Noah on January 8, 2001. However, the cloned animal died just two days later from a common dysentery infection, apparently unrelated to the cloning procedure or its gestation in a different species.
ACT had another, more lasting success in April 2003, when two cows gave birth to cloned bantengs, a type of Asian wild cattle. The donor cells were taken from a frozen sample stored at San Diego Zoo and implanted in 2002. Although one of the bantengs was euthanized shortly after birth, the other lived for seven years, dying in April 2010. While it survived longer than any previous interspecies clone, the cloned banteng lived for less than half its species' normal life span.
The first clone of a fully extinct species was born in January 2009. Scientists at Spain's Centro de Investigación y Tecnología Agroalimentaria de Aragón (Agrifood Research and Technology Centre of Aragon) implanted DNA taken from frozen skin samples of the Pyrenean ibex, which had been declared extinct in 2000, in the eggs of domestic goats. Of the over fifty embryos that were implanted, only one resulted in a live birth. The newborn ibex lived for seven minutes before dying due to lung defects.
In August 2011, a preserved baby wooly mammoth was discovered in Russia. Scientists from Russia's North-Eastern Federal University and Japan's Kinki University announced their intention to try to clone the creature, though experts expressed skepticism about the viability of any DNA that may be found. In 2017, researchers at Harvard University in Cambridge, Massachusetts, reported that they anticipated producing a functioning woolly mammoth embryo by 2020. The researchers at Harvard claimed they would use a different approach that does not rely on mammoth DNA, instead using genetic engineering technology to modify an elephant genome with mammoth genes to implant into an Asian elephant embryo, creating a hybrid embryo. Though researchers did not meet their 2020 deadline, the project continued in the 2020s with the new goal of creating the necessary conditions to produce a wooly mammoth by 2027. Specifically, the conditions and speed of the in vitro fertilization process were still being refined. While the work went on and lead researchers behind the project, who reported achieving an important breakthrough in 2024, argued that the de-extinction of the animal could contribute to the strengthening of ecosystems and combating climate change, an ethical debate persisted.
Future Challenges
A broader question involves the potential role of cloning in maintaining species and genetic diversity. It has been argued that the selective cloning of individual members of a species will lead to a reduction in genetic diversity due to a streamlined gene pool. This may ultimately affect the survival and adaptability of a species.
Moreover, cloning does not directly address the conditions that led to the loss of species fitness, which are reflected in reproduction and survival rates. In many instances, species become endangered due to a loss of habitat; thus, survival of the species may require long-term existence in captivity. In certain cases, attempts have been made to return animals bred in captivity to their natural habitat, but it was not clear that these efforts would be successful in general. The reproductive technologies and long-term effects of captivity may have serious consequences on the survival of the species once it is reintroduced to the wild. Some successes have been noted in this area; for example, in the 1980s, the American peregrine falcon was reintroduced into the wild in eastern North America, where it had become extinct due to the widespread use of the pesticide DDT.
Other problems associated with interspecies nuclear transfer and assisted reproductive technologies in general are their high cost and low success rate. It has been estimated that the average success rate of same-species nuclear transfer is between 1 and 3 percent. The success rate for interspecies nuclear transfer is considerably less. The ACT's attempts at interspecies nuclear transfer when cloning the gaur required almost seven hundred cow eggs, about eighty of which developed as suitable donors for transplantation. About forty of these were implanted into cows, which resulted in eight pregnancies and ultimately only one live birth.
Despite these concerns, zoological parks have collected sperm and eggs from many types of animals in the form of “frozen zoos,” which may serve as genetic repositories for producing animals of the future. In addition, the San Diego Zoo’s Institute for Conservation Research and the Audubon Center for Research of Endangered Species have sponsored animal-tissue banks that could be the future source of cloned animals to safeguard species from extinction. The genetic material for the cloned bantengs was taken from the tissue bank at the San Diego Zoo. By 2024, researchers had succeeded in cloning the endangered black-footed ferret using genetic material frozen at San Diego's facility.
The death of a species by extinction engenders a sense of profound loss as it brings to a close a chapter of evolutionary and biological history. It may also disrupt the delicate balance of life, as species interdependence is a fundamental component of ecological systems. As efforts to save individual species from permanent extinction by the cloning of selected members are applauded, it is important to reflect on the conditions and circumstances that have contributed to their loss.
Principal Terms
Biodiversity: the variety of plants, animals, and habitats and the interactions among these species
Biotechnology: the use of the tools of recombinant DNA technology to study or modify biological systems
Cloning: the reproduction of an individual to create an offspring that is genetically identical to its parent
Extinction: the dying off of all individuals of a species
Gene Pool: the collection of genes or genetic information in a population of individuals
Nuclear Transfer: the insertion of genetic material from a donor cell into a recipient cell; in reproductive technologies, the recipient cell is an egg cell from which the nucleus has been removed
Bibliography
Ashworth, James. “Extinction Threat to Primates Threatens Greater Diversity Loss Than First Thought.”Natural History Museum, 30 Sept. 2021, www.nhm.ac.uk/discover/news/2021/september/extinction-of-primates-threatens-greater-diversity-loss.html. Accessed 8 July 2023.
Bethge, Philip. "Preservation in a Petri Dish: Scientists Hope Cloning Will Save Endangered Animals." Spiegel, 11 Aug. 2012, www.spiegel.de/international/world/scientists-hope-interspecies-cloning-will-save-endangered-animals-a-865932.html. Accessed 18 Sept. 2013.
Chadwick, Douglas, and Joel Sartore. The Company We Keep: America’s Endangered Species. National Geographic, 1996.
Corley-Smith, Graham E., and Bruce P. Brandhorst. “Preservation of Endangered Species and Populations: A Role for Genome Banking, Somatic Cell Cloning, and Androgenesis?” Molecular Reproduction and Development, vol. 53 no. 3, 1999, pp. 363–67.
Dutchen, Stephanie. “A Mammoth Solution.” Harvard Medical School, 12 Nov. 2021, hms.harvard.edu/news/mammoth-solution. Accessed 8 July 2023.
Grandoni, Dino. "Can Scientists Clone an Endangered Species Back from the Brink of Extinction?" The Washington Post, 17 Apr. 2024, www.washingtonpost.com/climate-environment/2024/04/17/black-footed-ferrets-cloned-noreen-antonia/. Accessed 6 Aug. 2024.
Gray, Richard, and Roger Dobson. "Extinct Ibex Is Resurrected by Cloning." The Telegraph, 31 Jan. 2009, www.telegraph.co.uk/news/science/science-news/4409958/Extinct-ibex-is-resurrected-by-cloning.html. Accessed 18 Sept. 2013.
Lanza, Robert P., Betsy L. Dresser, and Philip Damiani. “Cloning Noah’s Ark.” Scientific American, 2000, pp. 84–89.
Myers, Norman, et al. “Biodiversity Hotspots for Conservation Priorities.” Nature, 2000, pp. 853–58.
Sample, Ian. "Woolly Mammoth DNA May Lead to a Resurrection of the Ancient Beast." The Guardian, 30 July 2013, www.theguardian.com/science/2013/jul/31/woolly-mammoth-dna-cloning. Accessed 18 Sept. 2013.
Shapiro, Beth. How to Clone a Mammoth. Princeton UP, 2015.
Stein, Rob. "Scientists Take a Step Closer to Resurrecting the Woolly Mammoth." All Things Considered, NPR, 6 Mar. 2024, www.npr.org/sections/health-shots/2024/03/06/1235944741/resurrecting-woolly-mammoth-extinction. Accessed 6 Aug. 2024.
Tilson, Ronald, and Philip J. Nyhus, editors. Tigers of the World: The Biology, Biopolitics, Management, and Conservation of Panthera tigris. 2nd ed., Academic, 2010.
“Why Are So Many Animals Endangered?” American Museum of Natural History, www.amnh.org/explore/ology/earth/ask-a-scientist-about-our-environment/why-are-so-many-animals-endangered. Accessed 6 Aug. 2024.
Wray, Britt. Rise of the Necrofauna: The Science, Ethics, and Risks of De-Extinction. Greystone Books, 2017.