Is This Futuristic Work the Answer to Animal Species Extinction?

Protecting animals against environmental changes, poachers, and other dangers is vital yet challenging work. And in recent years, things have seemed dismal. The International Union for Conservation of Nature (IUCN) Red List of Threatened Species is the world’s most comprehensive list on the global extinction risk of animal, fungus, and plant species. Recent estimates show that of the 166,000 species on the Red List, 41% of amphibians, 37% of sharks, 26% of mammals, 26% of freshwater fishes, and 12% of birds are threatened with extinction. It’s bleak and arguably heartbreaking.

But thanks to the hard work of many people around the world, recent advancements in the field of biobanking offer hope that one day we may finally put a stop to animal species’ extinction. One pioneer in this space is the Frozen Zoo located at the San Diego Zoo, which is already doing some incredible work for endangered species.  

What Is the Frozen Zoo?

The Frozen Zoo is a biological sample repository, which is the largest and most diverse collection of its kind in the world. The San Diego Zoo Wildlife Alliance (SDZWA), an international nonprofit conservation organization, manages the Frozen Zoo inside its Wildlife Diversity Biobank. It was established 50 years ago and now houses more than 11,420 living cell cultures, which include more than 1,330 species and subspecies.

Dr. Kurt Benirschke founded the Frozen Zoo in 1975. “[His] interest in chromosomes led to studying zoo animals and banking their cells,” explains Oliver Ryder, Ph.D., Director of Conservation Genetics at the San Diego Zoo Wildlife Alliance. “Yet, he also understood there would be greater potential for the collection as technology progressed.”

How Does It Work?

Samples of living skin cells, gametes (sperm and egg), and reproductive tissues of mammals, birds, reptiles, amphibians, and fish are stored in liquid nitrogen freezers at -320 degrees F in cryogenic tanks. From there, these cells can be used to help animals both now and in the future.

According to Dr. Ryder, these samples have regularly “found wide use and application to human and wildlife health; the fields of comparative and evolutionary genomics; assessing, monitoring, and managing animal populations under human care in the wild; and, recently, genetic rescue.”

How is the Frozen Zoo Helping in Wildlife Conservation of Endangered Species?

“Living skin cells can be used for chromosome studies, genome sequencing, and bringing species back from the brink of extinction through population management to minimize harmful consequences of inbreeding and genetic rescue techniques, such as cloning, to restore the genetic diversity of wildlife populations,” explains Dr. Ryder. “They can also be reprogrammed to become induced pluripotent stem cells (iPCS), which can become any cell in the body, including sperm and eggs.”

For example, the Frozen Zoo has brought back valuable genetic diversity to animals, including the endangered black-footed ferret and Przewalski’s horse, which will increase the odds of their species’ survival.

The Cloning of Przewalski’s Horse Broke a Record

A 2025 study co-authored by Dr. Ryder identified how the Frozen Zoo’s ability to clone animals from historically cryopreserved cells can help in conservation efforts. Approximately all 1,800 living Przewalski’s horses, known as the last wild horses, were descended by 12 horses captured from the wild between 1898 and 1947. This lack of genetic diversity challenges the species’ survival.

However, the San Diego Zoo Wildlife Alliance had living cell lines from a stallion, who lived from 1975-1998, frozen in their Frozen Zoo. Researchers were able to create two clones from this horse in new horses named Kurt and Ollie, marking the first time that more than one healthy clone has been created from an endangered species. By introducing new genetic material, new Przewalski’s horses can be bred with a greater genetic diversity in the future, leading to hope for this species’ survival.

“Restoring genetic diversity in wildlife populations allows for greater chances of survival,” says Dr. Ryder. “In other words, high genetic diversity is crucial for species’ adaptability and resilience to environmental changes. By utilizing cells frozen years ago, we can reintroduce an individual whose genetic diversity would have otherwise been lost forever, ultimately benefiting present-day and future populations.”

What Does This Mean for the Future of At-Risk Species?

The future of animal conservation is happening now. The National Human Genome Research Institute and the National Institutes of Health sequenced 131 new placental mammal genomes in a study published in the journal Nature in 2020. Dr. Ryder is one of the project’s co-authors, who said in a statement at the time, “Before the microscope, we couldn’t see what was going on inside of a cell. Now, we’re viewing life from an entirely new perspective. DNA carries instructions, and now we’re able to read those.”

By studying animal genomes, researchers can help determine which genetic mutations may be associated with risk of diseases like cancer and diabetes. Identifying the species’ extinction risks will give wildlife conservationists a map of how to protect and help vulnerable creatures.

In 2023, San Diego Zoo Wildlife Alliance partnered with the IUCN’s Species Survival Commission (SSC) to form the new Center for Species Survival: Biodiversity Banking. “[This will] further build upon biodiversity banking as a tool to conserve species,” Nadine Lamberski, DVM, Chief Conservation and Wildlife Health Officer at San Diego Wildlife Alliance, said in a press release at the time. This partnership will cultivate a network of conservation practitioners engaged in biodiversity baking to further protect wildlife around the world.

According to the SDZWA, the Frozen Zoo is currently working on several projects, including sequencing the genomes of 10,000 species to provide a new framework for biological inquiry; comparing Frozen Zoo samples with ancient DNA samples from the Russian Academy of Sciences; and studying how stem cell technology could rescue the northern white rhino from the brink of extinction, among other initiatives.

Recently, the Darjeeling Zoo in West Bengal, India, has started collecting and freezing DNA from endangered animals such as red pandas and snow leopards, per The Times. The San Diego Zoo Wildlife Alliance’s influence continues its global reach as all agencies work together to preserve the wonderful and unique animals with whom we share the earth.