Summary
The Mammal Society recognises the scientific achievement represented by recent advances in genome editing, including the high-profile announcement by Colossal Biosciences of grey wolf (Canis lupus) pups edited to display phenotypic traits associated with the extinct dire wolf (Aenocyon dirus). However, we do not consider such gene-edited animals to be resurrected or reconstituted extinct species, nor do we consider de-extinction, as currently practised, to be an effective conservation strategy. Genome editing technologies may have legitimate and valuable applications in the conservation of extant threatened species — for example, removing harmful mutations or restoring lost genetic diversity in small, inbred populations. The Mammal Society supports the continued, careful development of these applications. However, we caution strongly against the promotion of de-extinction as a substitute for addressing the continuing biodiversity crisis, and against the diversion of conservation funding, attention or public and political urgency away from the protection of existing species and their habitats.
Background
On 7 April 2025, Colossal Biosciences Inc. announced that it had used gene editing to create three grey wolf pups carrying edits intended to recreate phenotypic traits of the extinct dire wolf. Colossal framed this work as a conservation breakthrough, presenting de-extinction as a means of reversing biodiversity loss and restoring species to ecosystems from which they have been absent for millennia. The company has also suggested that the same technologies could be applied more broadly to prevent the extinction of currently threatened species. The IUCN SSC Canid Specialist Group (CSG) responded with a detailed commentary, noting that the dire wolf and grey wolf genomes differ by thousands of genes, whereas Colossal's editing was confined to a small number of loci in the grey wolf genome. The CSG concluded that the resulting animals are not dire wolves, nor are they legitimate conservation "proxies" of the dire wolf under the IUCN SSC's own guiding principles (IUCN SSC 2016), because there is no restored ecological niche or function for them to occupy, and no evidence that they are phenotypically distinct from grey wolves in any respect beyond the edited traits.
This case, although specific to canids, raises issues of much wider relevance to mammalian conservation and to the Mammal Society's remit. De-extinction projects targeting other mammals — including the woolly mammoth (Mammuthus primigenius) and the thylacine (Thylacinus cynocephalus) — have attracted comparable levels of commercial and media attention, and similar scientific and ethical questions arise in each case. This statement sets out the Society's position on de-extinction and related gene-editing technologies as they apply to mammals generally, drawing on the CSG's canid-specific commentary as a foundation and on the wider peer-reviewed literature on the ecology, genetics and conservation implications of de-extinction.
Position
1. Gene-edited proxies are not the extinct species. A small number of edited loci does not reconstitute the genome, phenotype or evolutionary history of an extinct species. Genomes of extinct and extant relative species typically differ at thousands to millions of sites, while published de-extinction projects have edited only a handful of genes (Ilic 2025). Therefore, functional "de-extinction" produces novel proxy organisms, not resurrected members of the original species, and these proxies inherit the genetic bottlenecks and reduced evolutionary potential of the source population used to create them (Steeves et al. 2017; Robert et al. 2017). Even extensive genomic editing cannot recreate the full evolutionary lineage, developmental history, socially learned behaviours, microbiome associations, or ecological relationships that shaped an extinct species over evolutionary time.
2. Proxies are unlikely to fully restore ecological function. The ecological niches, prey communities, competitors and environments that extinct species depended on have changed, often irrecoverably, since extinction. Reintroducing a phenotypic proxy into a transformed ecosystem risks producing what has been termed a "functionally ineffectual eco-zombie" rather than a restoration of ecosystem function (McCauley et al. 2017; Wood et al. 2017). Environmental suitability and the survival of the original ecological context should be treated as primary screening criteria for any de-extinction proposal (Seddon et al. 2014).
3. De-extinction carries a significant conservation opportunity cost. Funding, expertise and public attention devoted to de-extinction projects represent resources that could otherwise be directed towards the conservation of extant threatened species. Modelling of comparable prioritisation exercises indicates that resources spent reviving one extinct species could instead protect three to eight times as many living species from extinction, and that public investment in de-extinction risks producing a net loss of biodiversity (Bennett et al. 2017). High-profile revived proxies may also skew conservation prioritisation and management effort away from less charismatic extant species in genuine need (Iacona et al. 2017).
4. Promoting de-extinction as "reversing extinction" risks undermining conservation urgency. Presenting extinction as a reversible technological problem risks weakening public and political will to prevent extinctions in the first place — a concern raised consistently in the conservation ethics literature since at least 2014 (Sandler 2014), and one that expert surveys suggest is shared by a substantial proportion of conservation professionals (Valdez et al. 2019). Indeed, there is a risk that extinction rates will increase through complacency borne of the belief that a species can be restored later by de-extinction technologies. We note that the direct empirical evidence for this "moral hazard" effect is still emerging and mixed: the most rigorous test to date did not find that people were more willing to accept a species' extinction when de-extinction was promised, although it did find that extinction-acceptance was associated with a belief that de-extinction could succeed (Lean et al. 2025). The Mammal Society regards this as a serious and plausible risk, warranting caution in how de-extinction is communicated, even though it is not yet conclusively demonstrated.
5. The welfare of animals produced through de-extinction warrants serious consideration. The reproductive processes used to produce de-extinct animals (principally somatic cell nuclear transfer (SCNT)) are associated with high rates of embryonic and foetal loss, and serious developmental abnormalities in offspring. In ruminants only around 1–5% of transferred SCNT embryos result in live births, and Large or Abnormal Offspring Syndrome (characterised by organ defects, impaired lung function, and metabolic abnormalities) has been recorded in 31–58% of cloned individuals (Rivera et al. 2023; IJMS 2020). Surrogate animals bearing cloned embryos may be at substantially elevated risk of pregnancy complications, including hydrops (a serious and often fatal condition) for which risk is estimated at 13–61% in cloned pregnancies compared with 0.1–0.5% in naturally conceived ones, alongside high rates of late-gestation loss and caesarean delivery (Panarace et al. 2007; Heyman et al. 2002). The only animal ever born through de-extinction in the strict sense (being cloned using cells taken from frozen tissue samples after the death of the last animal of this species) was a Pyrenean ibex in 2003, and it died within minutes of birth from a lung malformation directly attributable to the cloning process (Folch et al. 2009). Welfare risks extend beyond birth: animals produced with no viable reintroduction pathway face long-term captivity without the ecological context, social learning, conspecific relationships or the acquisition of gut biomes that may be essential for processing normal diets etc. that their biology requires (Browning 2018; Harrington et al. 2013).
The Mammal Society considers that these welfare costs to produced animals and their surrogates must be considered in any assessment of a de-extinction proposal, and that they constitute a significant additional objection to de-extinction as currently practised.
6. Gene editing has legitimate, distinct value in conserving extant species. Applied to living, threatened populations rather than extinct ones, genome editing and related techniques may help remove harmful mutations, restore genetic diversity lost through historic and recent bottlenecks, and increase resilience to disease and environmental change (van Oosterhout et al. 2025). This builds on an established body of work on genetic rescue through managed gene flow, which the Mammal Society recognises as a valuable — if still carefully caveated — tool for small, inbred or isolated mammal populations (Whiteley et al. 2015; Bell et al. 2019). However, this can be done with stem cells rather than through nuclear transfer into adult cells. Any such interventions must complement, not substitute for, habitat protection and restoration and other core conservation actions, and should proceed only through phased trials with long-term monitoring.
7. De-extinction proposals should be assessed against the IUCN SSC's guiding principles. Any proposal to create a proxy of an extinct species for conservation benefit should be assessed against the IUCN SSC Guiding Principles on Creating Proxies of Extinct Species for Conservation Benefit (IUCN SSC 2016), which require, among other things, a clear a priori justification based on expected conservation gain. The Mammal Society endorses these principles as the appropriate international standard and, in line with the CSG's own assessment of the dire wolf case, considers that a project which produces no restored ecological niche or function, and no genuine evidence of extinct-species phenotype and genotype beyond the edited traits, does not meet this standard (IUCN SSC Canid Specialist Group 2025).
The Mammal Society considers it important to note that de-extinction, as a field, is being shaped primarily by commercial incentives and private investment rather than by conservation need or independent scientific governance. The concentration of a consequential and rapidly advancing area of biological research within a single commercially driven entity — rather than within the regulated, peer-reviewed structures that ordinarily govern conservation science — raises legitimate questions about transparency, the integrity of public claims, and whether findings are communicated in line with established scientific norms. The Society does not consider this an argument against the underlying science, but it is an argument for independent oversight, rigorous peer review, and caution in how de-extinction announcements are received by policymakers, media and the public.
Taken together, the Mammal Society's position is that mammal conservation priorities are best served by protecting extant species and the habitats and ecological processes that sustain them, that genome-editing technologies have a genuine but specific and limited role to play in that effort when applied to living populations, and that de-extinction should not be presented to the public, policymakers or funders as a solution to the biodiversity crisis.
References
Bell D.A., Robinson Z.L., Funk W.C., Fitzpatrick S.W., Allendorf F.W., Tallmon D.A. and Whiteley A.R. (2019). The exciting potential and remaining uncertainties of genetic rescue. Trends in Ecology & Evolution 34(12): 1070–1079. https://doi.org/10.1016/j.tree.2019.06.006
Bennett J.R., Maloney R.F., Steeves T.E., Brazill-Boast J., Possingham H.P. and Seddon P.J. (2017). Spending limited resources on de-extinction could lead to net biodiversity loss. Nature Ecology & Evolution 1(4): 0053. https://doi.org/10.1038/s41559-016-0053
Browning H. (2018). Won't somebody please think of the mammoths? De-extinction and animal welfare. Journal of Agricultural and Environmental Ethics 31(6): 785–803. https://doi.org/10.1007/s10806-018-9755-2
Folch J., Cocero M.J., Chesné P., Alabart J.L., Domínguez V., Cognié Y., Roche A., Fernández-Árias A., Martí J.I., Sánchez P., Echegoyen E., Beckers J.F., Sánchez Bonastre A. and Vignon X. (2009). First birth of an animal from an extinct subspecies (Capra pyrenaica pyrenaica) by cloning. Theriogenology 71(6): 1026–1034. https://doi.org/10.1016/j.theriogenology.2008.11.005
Harrington L.A., Moehrenschlager A., Gelling M., Atkinson R.P.D., Hughes J. and Macdonald D.W. (2013). Conflicting and complementary ethics of animal welfare considerations in reintroductions. Conservation Biology 27(3): 486–500. https://doi.org/10.1111/cobi.12021
Heyman Y., Chavatte-Palmer P., LeBourhis D., Camous S., Vignon X. and Renard J.P. (2002). Frequency and occurrence of late-gestation losses from cattle cloned embryos. Biology of Reproduction 66(1): 6–13. https://doi.org/10.1095/biolreprod66.1.6
International Journal of Molecular Sciences (2020). Lessons learned from somatic cell nuclear transfer. International Journal of Molecular Sciences 21(7): 2314. https://doi.org/10.3390/ijms21072314
Iacona G., Maloney R.F., Chadès I., Bennett J.R., Seddon P.J. and Possingham H.P. (2017). Prioritizing revived species: what are the conservation management implications of de-extinction? Functional Ecology 31(5): 1041–1048. https://doi.org/10.1111/1365-2435.12720
Ilic D. (2025). Engineered proxies and the illusion of de-extinction. Stem Cell Reports 20(6): 102505. https://doi.org/10.1016/j.stemcr.2025.102505
IUCN SSC (2016). Guiding Principles on Creating Proxies of Extinct Species for Conservation Benefit. Version 1.0. Gland, Switzerland: IUCN Species Survival Commission, 18 pp. [Institutional document]
IUCN SSC Canid Specialist Group, Taxonomic Review Task Force (Kitchener A., Sacks B., Sillero C., Chavez D., Machado F., Werhahn G., Senn H., Marino J., Cairns K., Hennelly L., Hoffmann M. and Viranta S.) (2025). Conservation perspectives on gene editing in wild canids: Commentary on the announced re-creation of a genetic proxy of an extinct dire wolf by Colossal. IUCN SSC Canid Specialist Group, 18 April 2025. [Institutional document]
Lean C.H., Latham A.J., Sandrussi A. and Rogers W. (2025). De-extinction and the risk of moral hazard. Biological Conservation 312: 111384. https://doi.org/10.1016/j.biocon.2025.111384
McCauley D.J., Hardesty-Moore M., Halpern B.S. and Young H.S. (2017). A mammoth undertaking: harnessing insight from functional ecology to shape de-extinction priority setting. Functional Ecology 31(5): 1003–1011. https://doi.org/10.1111/1365-2435.12728
Panarace M., Aguero J.I., Garrote M., Jauregui G., Segovia A., Pfirter L., Lagioia J., Basualdo M., Enrique A., Magnarelli G., Ravello E., Gross E., Medina M. and Melo M. (2007). How healthy are clones and their progeny: 5 years of field experience. Theriogenology 67(1): 142–151. https://doi.org/10.1016/j.theriogenology.2006.09.036
Rivera R.M., et al. (2023). Review: Large offspring syndrome in ruminants — current status and prediction during pregnancy. Animal 17(1): 100740. https://doi.org/10.1016/j.animal.2023.100740
Robert A., Thévenin C., Prince K., Sarrazin F. and Clavel J. (2017). De-extinction and evolution. Functional Ecology 31(5): 1021–1031. https://doi.org/10.1111/1365-2435.12723
Sandler R. (2014). The ethics of reviving long extinct species. Conservation Biology 28(2): 354–360. https://doi.org/10.1111/cobi.12198
Seddon P.J., Moehrenschlager A. and Ewen J. (2014). Reintroducing resurrected species: selecting de-extinction candidates. Trends in Ecology & Evolution 29(3): 140–147. https://doi.org/10.1016/j.tree.2014.01.007
Steeves T.E., Johnson J.A. and Hale M.L. (2017). Maximising evolutionary potential in functional proxies for extinct species: a conservation genetic perspective on de-extinction. Functional Ecology 31(5): 1032–1040. https://doi.org/10.1111/1365-2435.12843
Valdez R.X., Kuzma J., Cummings C.L. and Peterson M.N. (2019). Anticipating risks, governance needs, and public perceptions of de-extinction. Journal of Responsible Innovation 6(2): 211–231. https://doi.org/10.1080/23299460.2019.1591145
van Oosterhout C., Supple M.A., Morales H.E., Birley T., Tatayah V., Jones C.G., Whitford H.L., Tollington S., Ruhomaun K., Groombridge J.J., Brickson L., Keyte A.L., Shapiro B., James M. and Turner S.D. (2025). Genome engineering in biodiversity conservation and restoration. Nature Reviews Biodiversity 1: 543–555. https://doi.org/10.1038/s44358-025-00065-6
Whiteley A.R., Fitzpatrick S.W., Funk W.C. and Tallmon D.A. (2015). Genetic rescue to the rescue. Trends in Ecology & Evolution 30(1): 42–49. https://doi.org/10.1016/j.tree.2014.10.009
Wood J.R., Perry G.L.W. and Wilmshurst J.M. (2017). Using palaeoecology to determine baseline ecological requirements and interaction networks for de-extinction candidate species. Functional Ecology 31(5): 1012–1020. https://doi.org/10.1111/1365-2435.12773