Every year, more and more species of plants and animals are declared extinct— meaning that there are no living members of the species left. In the past, extinction was brought on by various natural reasons, including gradual changes in climate and natural disasters such as volcanoes, floods, and fires. Now, the biggest factor causing species to go extinct is the influence of humanity. Humans are causing extinctions to happen at the fastest rate in history, through destruction of habit as well as influence on global temperatures. So what can we do to fix it? The first steps are in the conservation of remaining habitats and species, changing the way we interact with our environment. Soon it may be possible to go even farther than conserving current wildlife; soon, we may be able to bring back those species that are already gone.
De-extinction is the general name for processes of bringing back species that have gone extinct. There are multiple methods to achieve this goal. Here I will explore three such methods: cloning, genome modification, and selective breeding.
The idea of cloning an animal is one that’s very popular and often sensationalized by the media. But how does it really work? Cloning starts by extracting the DNA-containing nucleus from a cell belonging to the animal to be cloned. This nucleus is then inserted into an enucleated (deprived of its nucleus) egg cell which, in the case of mammals, is transferred into a surrogate mother of the donor species once it starts to divide and grow. Once born, the clone is a genetic twin to the original donor of DNA; however, this includes such drawbacks as telomere shortening (genetic aging). This has successfully been done many times over the years. The first such clone of a living animal was Dolly the sheep in 1997. A group of scientists in Edinburgh, Scotland took the nucleus of a cell from an adult sheep and transferred it to the egg cell of another sheep. Their success was the first evidence that a clone could be made using an adult cell. Since then, many different species of living animals have been cloned, including the endangered Indian bison.
The next step towards de-extinction via cloning is to clone one that is no longer living. The first progress made towards the reincarnation of an extinct species occurred in 2009. Spanish researchers took frozen tissue from a recently extinct species of wild goat, Capra pyrenaica pyrenaica, which had been frozen for just this reason. They inserted its genetic material into a closely related species to act as surrogate mother, since there were (obviously) no members of the original goat species remaining. The result was the birth of a living C. pyrenaica, although it only survived for a few minutes past birth due to respiratory defects.
Despite the results of these experiments, there is still an issue that needs to be addressed before we can truly bring back any extinct species. In the case of C. pyrenaica, there was tissue frozen preserved in advance for use in the cloning process. With most extinct species, especially long extinct ones, this is not the case. How do we solve that problem? There are a couple of ways.
The first is by extracting DNA from fossils. Now, most of the time this isn’t plausible. Once an organism is no longer living, DNA breaks down at a fairly fast rate. There is research that has been done measuring these rates, which tells us that the half-life of DNA is a little over 500 years in fossilized tissues. This means that in 500 years, half of a DNA sample will have degraded. The result of this is that any animal which went extinct over 500 years ago is usually not going to be something we can bring back just by using cloning methods. That being said, there is an exception found in one famous extinct animal: the woolly mammoth. Woolly mammoths lived in the cold arctic northern regions of North America, where they were hunted to extinction by early humans. Because many fossilized remains were frozen in ice, its DNA did not degrade completely and could potentially be pieced together; this is currently a work in progress. For any species that are nearing extinction, a frozen sample of tissue can also be collected, like in the case of our Spanish goat, so that it can later be cloned back into existence.
Another solution for filling in missing DNA is through a process called genome modification. This involves taking a close relative to the extinct species, which has a very similar sequence of DNA (relatively speaking). If most of the genome of the extinct species can be pieced together using fragments of DNA collected from preserved tissues, a close enough relative could be used to fill in the holes. From here, the same process as cloning would be used to turn this DNA into a living animal: it would be inserted into the egg cell of its closest living relative. An example of this being done in science is in the recently extinct passenger pigeon, whose partial DNA is accessible from toe pad tissues of preserved specimens. This species was killed off entirely by humans, but has close living relatives such as the carrier pigeon which may help us pieces together its lost blueprint.
The final method I’m going to talk about is a little less sci-fi than cloning and genome modification: selective breeding. If you have a pet dog, you have seen the effects of selective breeding done by humans. It is the process of selecting desirable traits in individuals of a species, and breeding those individuals together to carry on the desired traits. This method only applies to species with a descendent that is still living. In the context of de-extinction, a domestic species would be taken, and bred to select traits that were found in its wild ancestors. This, after many generations, would produce an animal that is able to survive on its own as the ancestral species once did. Such“breeding back” has already been accomplished to a small extent: there is a population of cows known as Heck cattle that were bred in the 1940’s to resemble their wild ancestor, the auroch. This population is now living completely independent of humans in a wildlife preserve in Europe, representing the first species of bovine to live in the wild in Europe in centuries.
Whether or not humans “owe it” to the species that we have caused to become extinct, or whether it is just a novelty that will never be widespread, the concept of being able to bring back a lost species is a fascinating one. And now, with methods such as the ones described above, this fascinating and incredible concept may become a reality in the future.