The concept of de-extinction, the process of generating an extinct organism, has so far largely focused on popular animals such as mammoths or even dinosaurs. But in a new study, a team of paleo-geneticists looked at Rattus maclearithe Christmas Island rat, which died out 199 years ago — a much more realistic case study.
Tom Gilbert, an evolutionary geneticist at the University of Copenhagen, Denmark, and his team agree that their choice is not the most sensational, but they argue that it is the most feasible with today’s technology. They looked at how the extinct rat could be reanimated as well as the limits of de-extinction, addressing important questions about how something like this should be done.
When working with the genome of an extinct species, scientists face the challenge of working with degraded DNA, which does not have all the genetic information needed to reconstruct a complete genome of the animal. But with the Christmas Island rat, which is thought to have disappeared due to illnesses brought on board European ships, the researchers were in luck.
They sequenced the rat’s genome and found that they were able to retrieve almost all of the genetic information. It turns out that the Christmas Island rat is closely related to a living rat species, the Norway brown rat, sharing about 95% of its genome. This has become very convenient, because when sequencing the genome, researchers have to compare it to a modern reference.
There are also ethical concerns in bringing back an extinct species, they argued, the main one being that the money could instead be invested in the conservation of animals that are still alive. But whether something like this could be done is indeed interesting and could be important for particular keystone species.
The Possibilities Behind De-Extinction
In their paper, the researchers described the three most touted methods of de-extinction: back-breeding (breeding ancestral traits in modern animals), cloning, and gene editing.
The researchers focused on gene editing. Basically, this means modifying the genes of an existing animal to resemble those of the animal you are trying to bring back. They sequenced ancient DNA from two skin samples taken between 1900 and 1902. By comparing the genome to several modern rats, they were able to identify traits of the extinct rat that they could replicate.
With this method, a resurrected animal would not be like the extinct group, there would be some differences. But in this case, there are many similarities between the extant rat and the extinct rat, which would replicate several key aspects of the extinct species.
However, the genes involved in smell in the Christmas Island rat were so different that the olfactory genes in the Norwegian rat did not provide a good basis for reconstructing them. Genes related to the immune response were also not covered. The researchers argue that any resurrected species would benefit from Norway rat immune genes.
The study was a proof of concept more than anything else. The researchers showed how deextinction could be achieved by using genetic editing of an existing species to bring back a related one, but have no plans to bring back rats yet.
While we won’t be seeing the Christmas Island rat again anytime soon, the study has opened the door to discussing deextinction and its potential outcomes and benefits — and maybe that’s a conversation we should be having. sooner rather than later.
“We don’t plan on doing that, because the world probably doesn’t need rats anymore, and probably the money it would take to do the best job possible could be spent on better things, for example, conservation of rats. living things,” Gilbert said in a statement.
The study was published in the Cell magazine.