To Clone or Not to Clone, That Is the Question…

By: Shayna Vercillo

Tucked away in the Arnold and Mabel Beckman Center for Conservation Research at the San Diego Zoo resides what many might consider a science fiction oddity. Kept with care and watchful monitoring, the Beckman Center for Conservation Research contains a peculiar collection, the largest of its kind: the Frozen Zoo.[1]

At its core, the Frozen Zoo contains the genetic material of bygone animals. More specifically, the collection houses “over 10,000 living cell cultures, oocytes, sperm, and embryos representing nearly 1,000 taxa, including one extinct species, the po’ouli.”[2] Moreover, scientists at the Frozen Zoo emphasize that the collection is “a crucial resource for facilitating advances in genetic and reproductive technologies for population sustainability.”[3] The Frozen Zoo is the salvation of imperiled species facing the ultimate consequence of human action and inaction—extinction.

The Frozen Zoo was started over 40 years ago—before cloning or current reproductive technologies even existed—by a San Diego Zoo geneticist, Dr. Kurt Benirshke.[4] Even then, Dr. Benirshke had the foresight to anticipate the significance of preserving genetic diversity for the continuation and persistence of endangered species in the near, and quickly encroaching, future.

Consequently, Dr. Benirshke’s initiative and forethought have been integral to current genetic conservation and assisted reproduction technologies for endangered wildlife.[5] Notably, the Frozen Zoo has been essential to developing artificial insemination methods and to researching genetic rescue through cloning.[6] In 2020, Kurt the Przewalski’s horse was the first successful clone of the endangered horse species native to Central Asia.[7]  Revive & Restore and ViaGen Pets & Equine, both genetic preservation and biotech organizations, collaboratively used cryopreserved cells of a genetically diverse stallion from 1980 to create a foal whose existence consists of genetic material entirely absent from the extant Przewalski’s horse population.[8]

Most recently, and with great excitement, a cryogenically frozen sample has produced the first clone of an endangered species native to North America: a black-footed ferret named Elizabeth Ann.[9] On December 10, 2020, the birth of Elizabeth Ann marked an arrival three decades in the making since the original cells of a black-footed ferret named Willa were first donated to the Frozen Zoo in 1988. [10] Elizabeth Ann is Willa’s clone, and scientists hope Elizabeth Ann’s entirely new genetic lineage will add much needed genetic diversity to the current black-footed ferret population that is entirely descended from only seven individuals.[11]

While the existence of Kurt, and now Elizabeth Ann, might at first blush appear to be the results of a fringe science experiment, their creation is actually the next, deliberate step in a wide-sweeping plan for species conservation.[12] Scientists are currently concerned with the lack of genetic diversity in living populations of endangered species.[13] With reduced breeding, limited populations can become increasingly susceptible to health disorders, abnormalities, and disease from insufficient genetic diversity.[14]  Conservationists have found that, even when an endangered species has been able to regroup in numbers, the inbreeding that has increased the population has also impaired the overall health of the population, therefore undermining the species’ future sustainability. [15]

Enter the clone. To provide a genetic jump-start to a genetically encumbered species, cloning could reintroduce genetic lineage that is no longer represented within the current living population.[16] The U.S. Fish and Wildlife Service approached Revive & Restore in 2013 with this precise goal in mind—to explore cloning to increase the genetic diversity of North America’s black-footed ferrets.[17] In 2018, Revive & Restore received the first Fish and Wildlife Endangered Species Recovery Permit to research cloning an endangered species.[18]

Following Elizabeth Ann’s success, Mr. Ben Novak, the lead scientist for Revive & Restore, plans to move forward cautiously. Elizabeth Ann will live her life at the conservation center in Colorado.[19] Then when she is ready to breed, she will mate with another clone. [20] And finally, her offspring will be bred back with wild black-footed ferrets which will integrate her gene-pool into the wild population, enriching their genetic lineage.[21]

But larger ethical questions still remain: what are the consequences of breeding cloned individuals into wild populations? Should individual animals even be created in the first place when their lives will be spent entirely in conservation centers? How do we decide which endangered species deserve a cloning program? And, is cloning really a band-aid on a bullet hole, unwisely diverting our attention from the underlying causes of species degradation and biodiversity loss?[22] The Frozen Zoo might be a fantastical lifeline for many endangered species, but we, as environmental stewards, must always strive to ask ourselves: why do we need a frozen zoo in the first place?

Image from Revive & Restore

[1] Frozen Zoo, San Diego Zoo Inst. for Conservation Rsch., (last visited Mar. 2, 2021) [hereinafter Frozen Zoo].

[2] Id.

[3] Id.

[4] The Przewalski’s Horse (Takhi) Project, Revive & Restore, (last visited Mar. 2, 2021) [hereinafter Przewalski’s Horse Project].

[5] Frozen Zoo, supra note 1.

[6] Id.

[7] Przewalski’s Horse Project, supra note 4.

[8] Id.

[9] Sabrina Imbler, Meet Elizabeth Ann, the First Cloned Black-Footed Ferret, N.Y. Times (Feb. 18, 2021),; see also The Black-Footed Ferret Project, Revive & Restore, (last visited Mar. 2).

[10] Imbler, supra note 9.

[11] The Black-Footed Ferret Project, supra note 9; Katelyn Weisbrod, Warming Trends: A Baby Ferret May Save a Species, Providence, R.I. is Listed as Endangered, and Fish as a Carbon Sink, Inside Climate News, (Feb. 27, 2021),

[12] Przewalski’s Horse Project, supra note 4; The Black-Footed Ferret Project, supra note 9; see also Katelyn Weisbrod, supra note 11.

[13] Przewalski’s Horse Project, supra note 4; Imbler, supra note 9.

[14] Imbler, supra note 9; Weisbrod, supra note 11.

[15] Przewalski’s Horse Project, supra note 4.

[16] Id.

[17] Imbler, supra note 9.

[18] The Black-Footed Ferret Project, supra note 9.

[19] Imbler, supra note 9.

[20] Id.

[21] Id.

[22] See University of Adelaide, Don’t Focus on Genetic Diversity to Save Our Species, ScienceDaily, (Feb. 23, 2021),


  1. What an interesting article, Shayna! The ethical question behind cloning is a controversial one, but I was definitely intrigued by the potential benefits stated in your post. Specifically, the possibility of reintroducing black-footed ferrets into the wild, while at the same time enriching their genetic pool to decrease the detrimental health effects of inbreeding. Thanks for sharing!

  2. Hi Shayna!

    This article is super fascinating as I’ve never even considered the use of cloning to benefit endangered species. I think you raise some incredibly pertinent questions at the end of your post. Sometimes when humans interfere with wild populations they just make things worse, such as when humans removed wolves from Yellowstone. Thus, I could easily see this going wrong, especially if humans start to breed specific genetics into wild populations to solely benefit humans. I also agree that this may be a temporary fix, but this will not solve the loss of biodiversity. If we don’t solve the underlying issues such a climate change, we will be continually be trying to catch up with those effects and never actually solve the problem.

  3. Such an interesting article, Shayna! When I visited the San Diego Zoo, I actually learned about their plans for genetic cloning as a means of species survival. Definitely a very controversial topic, it makes me think we’ve learned nothing from Jurassic Park!

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