Revival Criteria

From the perspectives of conservation biology and molecular biology, criteria are emerging for determining which species are the best candidates for genetic rescue.

Genetic rescue comes in two forms, two degrees of difficulty…

  • Genetic assistance works with living species that are endangered in part because of their genetic predicament.  Their population may be so small that there are inbreeding problems.  They may be incapable of evolving fast enough to stay ahead of novel diseases or to keep up with climate change.  (Sometimes “genetic assistance” is referred to as “facilitated adaptation.”) It is relatively easy to adjust a living genome.
  • De-extinction uses genetic technology and DNA from museum specimens or fossils to revive species that have gone totally extinct.  Bringing an extinct genome back to life will be far from easy.  It may prove impossible.

Criteria for genetic assistance candidates fall into two broad categories…

  • Does the endangered species suffer from a loss of genetic diversity resulting in inbreeding problems and loss of adaptive resilience?  Small populations or populations grown from few founders may have difficulty reproducing because of inbreeding issues such as poor sperm viability, erratic ovulation, or increased juvenile mortality.  Often a cause is the population becoming more homozygous for deleterious genes.  Genetic treatment can restore heterozygosity. It may even be possible to restore “extinct alleles” from museum specimens so that the living population is similar in genetic robustness to the original wild population.
  • Does the endangered species suffer from lethal susceptibility to a new disease? One by-product of globalization is the spread of diseases that endangered species cannot adapt to quickly enough to survive. Examples include chytrid fungus in frogs worldwide, white-nose syndrome in bats, avian malaria in birds, and plague in North American rodents and carnivores.  Genetic treatment may be able to provide disease resistance which could propagate through the population.

Criteria for de-extinction candidates fall into three broad categories…

  • Can an individual of the organism of the species be brought back?   DNA must be available from museum specimens or fossils (less than 500,000 years old).  There must be a closely related living relative and a potential surrogate parent.  Dinosaurs left no DNA.  The giant ground sloth (megatherium) was too enormous for any living sloth to parent.
  • Can a viable population be brought back?   Can the species be captive-bred? Has the original cause of extinction been detected and resolved?  Is there habitat for the animals to return to?  Habitat has been restored for the ivory-billed woodpecker but not yet for the Chinese river dolphin (baiji).
  • Should the species be brought back?  Ecological, ethical, cultural, social, legal, and economic issues must be explored and resolved.  Are we eager to have saber-toothed cats back in the wild?  How about a bat that might be a vector for human disease?

Revive & Restore supports the IUCN’s guiding principles for de-extinction developed by the Species Survival Commission, and was an active participant in the review process for these criteria. For more information, please review the IUCN’s Guiding Principles on Creating Proxies of Extinct Species for Conservation Benefit, published in May 2016.