The Return of Extinct Species

Did you know we offer a Winter School course in Communicating Science? If you’re interested in science writing for both specialist and non-specialist audiences, presenting to communicate science and the use of emerging online social media in science communication, this is a great course for you. If you’re interested, check out “Communicating Science” in course outlines for more details.

Over the coming weeks we’ll be showcasing blog posts written by Communicating Science students during their course last year. The next blog in the series is “The Return of Extinct Species” By Patrick Capon.


A discussion on if and how we may find mammoths in our backyards

Could this become reality sooner than we expect?

Could this become reality sooner than we expect?

Revival of extinct species (or DeExtinction) has been a topic of considerable debate recently, and has featured heavily in National Geographic in particular (herehere, and here to name a few). Debate became widespread into the public when successful cloning of Dolly the sheep was reported in the journal Nature in 1997. Perhaps the most well known target for revival is the woolly mammoth, but there are also other targets such as the passenger pigeongastric brooding frog, and (a little closer to home) the thylacine or Tasmanian tiger.

While it is all fun and games thinking about woolly mammoths running around in your backyard, there are many important questions that need to be considered before we dive in headfirst and attempt to bring extinct species back to life. A video from National Geographic sums up these questions quite well (but doesn’t really provide any answers).


From here in I will try to address some of the questions raised in the video:

Should we bring extinct species back?

The first, and arguably most important question is: should we even be bringing species back from extinction? These species went extinct for a reason, or a combination of reasons. We need to consider what those reasons were, and whether interfering with ‘survival of the fittest’ will have a negative impact on the ecosystem. That said, it is easy to argue that humans are often the leading cause of more recent extinction events. There are two main human influences; hunting and removal of habitat. This can be seen today: take the case of habitat loss for orangutans or other rainforest species among the islands of Indonesia and Malaysia. A recent example of hunting to extinction is the thylacine, where a bounty rewarded for dead thylacines in Tasmania led to their extinction in the 1930s. People opposed to reviving extinct species suggest that we would be playing god, however Hank Greely (see the video above) counters this by asking ‘did we play god when we drove most of these species to extinction?’. In these cases, it could be considered our responsibility to return extinct species to their original place to the ecosystem.

How do we choose a target?

Assuming the debate on ‘should we revive extinct species’ is resolved, how would we begin to choose target species? There are hundreds of species that have been declared extinct and it seems an overwhelming task to choose a revival target or targets. This choice is reliant on public opinion, perceived benefit of revival, and technical feasibility. Public opinion is needed in order to generate any support for the revival program, especially in terms of funding required. Perceived benefit is crucial, as there needs to be a driving force beyond scientific curiosity in order to generate public backing and also to receive funding for the project. Lastly, the project must be technically feasible. This requires viable methods to even achieve the revival of the extinct species.Revival project feasability is well covered in this work, which contains a set of ten questions for use in determining if a species may be revived and re-introduced with some level of success.

How do we revive a species?

There are two main, currently active, approaches that can be taken toward reviving an extinct species. Firstly, and definitely the most well understood publicly, is cloning of extinct species. This method requires preserved tissue from the animal, in order to obtain DNA. This DNA sample is used to sequence the genome of the desired species, which can subsequently be spliced into eggs of a surrogate, related species. For example, the genome of a woolly mammoth may be inserted into an elephant egg to acheive pregnancy.This process was first successfully performed by Folch and colleagues with an extinct species of wild goat, with the modified embryo coming to term in a Spanish ibex. However this process is far from perfect, the research group started with 497 embryos, but had only five pregnant recipients, and only one came to term (see the table below). The single goat born survived only seven minutes, dying from a severe lung deformity. That said, it is highly promising and certainly paves the way for further work. This method could work for many species, see the second video here from National Geographic about the passenger pigeon.

Trial Reconstructed embryos No. of Cleaved embros at 36 hr (%)a No. of Embryos transferred (%)b No. of recipients Pregant recipients (45 d) Pregnant recipients (term)
1 107 52 (48.6) 44 (84.6) 11 1 1
2 127 75 (59.1) 24 (32.0) 6 0 0
3 99 45 (45.5) 24 (53.3) 9 3 0
4 164 63 (38.4) 62 (98.40 18 1 0
Total 497 235 (47.3) 154 (65.5) 44 5 1

a Only embryos with at least 3 cells were considered.
b Most transferred embryos were at the 4 cell stage.

Table of embryo trials adapted from this paper by J. Folch et al.

The second method is referred to as back breeding, and is currently active in the Rewilding Europe program, which attempts to return the auroch, the ancestor of the modern domesticated cow. Aurochs are desired as they play a key role in maintaining biodiversity. Back breeding relies on selecting breeding partners based on auroch-like characteristics, and attempting to move toward a pure auroch over several generations. Parts of the auroch genome have been unravelled and therefore the program can be advanced faster, as the breeding may target genes known to generate auroch characteristics with greater efficiency. This will hopefully lead to the return of the auroch, or a species extremely close to it.

Several other questions remain unanswered, including to what extent do we bring species back from extinction? As pure lab curiosities or eventual reintroduction into the wild? Population (and hence genetic) diversity needs to be obtained, which is difficult to achieve starting from only a few breeding pairs. Thylacines have been shown to have suffered from poor genetic diversity prior to their extinction – could this happen again?

An interesting and unique way of giving birth demonstrated by the gastric brooding frog. Photo from this site.

An interesting and unique way of giving birth demonstrated by the gastric brooding frog. Photo from this site.

Not all these questions have answers that are immediately obvious, and most require further research. Perhaps the most pertinent question is: why concentrate on something that is extinct, when we can concentrate on saving species that are endangered right now? My view is that re-introduction of extinct species is a long shot at this point in time, but we could certainly learn something by returning select species at a lab level. Take the gastric brooding frog – the female swallows the eggs and the young come to term in the mother’s stomach. There is certainly scope for learning here, whether through investigation of survival of the eggs in the digestive system, or how the mother is able to alter her tissue from stomach to uterus in order to grow young. Hopefully study into extinct species can put the brakes on currently endangered species teetering toward extinction.

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