We are in the midst of the sixth mass extinction, and humans are to blame. According to World Wildlife Fund, since 1970 there has been a 58% decline in numbers of fish, mammals, birds, and reptiles worldwide, which means that 2% of species are vanishing across the globe each year (1). Around 30 to 159 species are disappearing every day (2). If action isn’t taken, two-thirds of the world’s wildlife could disappear by 2020.
What if there was a way to solve this problem? A way to bring back extinct animals? A term coined de-extinction may do just that. As scientists work on a way to bring extinct animals back to life, here are three main methods currently proposed:
The first and most obvious method is cloning. However, we can only use cloning if viable DNA is available to reconstruct the genome of the creature. That’s not the case for all extinct species. It may be a way forward for reintroducing thylacine, also known as the Tasmanian tiger, into our fauna. It has been discovered that museum-preserved fossils can be used to extract viable genetic material from the teeth, skins, and dried tissues, which can then be used to construct the whole genome. Once the genome is complete, there are two possible routes to produce a viable pup:
- The first method would be to add a synthetic thylacine cell to the egg of a Tasmanian devil, which is closely related to the extinct thylacine, with its nucleus removed. The modified egg would be implanted into the uterus of a female devil and one can only hope to see a thylacine pup coming into the world.
- The second and less invasive route would be to splice the DNA of the Tasmanian devil until it resembles the DNA of the thylacine (3). A study in 2008 spliced the DNA of the devil until it was successfully spliced into the DNA of a mouse. There has been a recent relative success in using cloning to bring back an extinct species – a common goat gave birth to an extinct Pyrenean ibex, however, the infant only lived for 7 minutes due to lung problems (2).
Another approach would be to reverse engineer the genome of a species that is phylogenetically close to the extinct animal. A relevant case study for this method is the passenger pigeon. Scientists are attempting to use its closest living relative, the band-tailed pigeon, to resurrect it. Geneticist George Church proposed to sequence the genomes of both pigeons and then tweak the genome of the band-tailed pigeon to make it genetically identical to that of the passenger pigeon. The biggest hurdle of this would be to combine all the desired traits into one bird (3). Another animal we can revive is the heath hen. By mutating the gene of the prairie chicken we may be able to get the prairie chicken to lay an egg that hatches to become a heath hen. In the case of resurrecting the heath hen, success is much more plausible as it has only 250,000 mutations, which make it different to the prairie chicken versus the passenger pigeon where the difference to the band-tailed pigeon is in 25 million mutations. One day we may even see the woolly mammoth walking the earth again, although so far there has been very little progress in its resurrection (4).
The third and simplest method is called the “breeding back” process. It gives hope for the revival of the aurochs – an ancestor of domesticated cows. The breeding back process involves strategic breeding in order to recreate the genome of the aurochs. This method has the advantage of not having to recreate an animal from a different time period and climate, as we can use living animals that currently exist. Some may not even consider it a true de-extinction because the procedure resembles selective breeding with the exception of using artificial insemination to pick out the desired traits in order to bring back the aurochs and fill in the missing ecological niche (4). Scientists are currently reconstructing the genome of the aurochs in order to “devise a blueprint” to see what make aurochs an aurochs (3).
There are many questions that de-extinction brings to the forefront of the environmental movement. Once we resurrect the animals, will they be able to live in the wild again? If de-extinction requires so many resources, why not focus on preserving the animals that are currently alive? Which animals should we focus on bringing back first? What we do know is the animals we are able to bring back will be not for the purposes of zoos. “The goal [has] to be about ecological restoration and function,” says Ben Novak, an ecologist and the leader of the passenger pigeon project at Revive & Restore. In the end, it is only at the stage of development and the future will harbor a much more profound debate over de-extinction (2).