By Olivia Marx
As a budding biologist, my non-scientist family and friends sometimes seek my expert opinion on matters of the life sciences. Do they ask me my professional opinion on today’s pressing issues, such as “should we get the COVID-19 vaccine?” or “when does a fertilized egg become a fetus?”. No, they have already formed opinions on such topics. What my family do care about, however, is when the science seen in science fiction movies is going to become possible. Namely, “Are you going to bring back the dinosaurs?” While my first inclination was to answer that I personally have no plans to start a Jurassic Park situation, the question did lead me to wonder what goes into bringing back extinct species and why we would even want to. So, let’s discuss the most pressing biological question that is not currently the subject of a polarizing political debate: How close is science to cloning dinosaurs?
What is required to bring back an extinct species?
The process of de-extinction, defined broadly as bringing back an extinct species, is not new. An early example is the 1951 de-extinction effort through back-breeding, in which Heinz Heck, a German biologist and director of the Hellabrunn Zoo, began selectively breeding cows until they resembled their extinct ancestor, the aurochs1, 2 (Fig 1A). While the resulting animals resembled the extinct aurochs, it remains debatable whether they truly represent the extinct species. More recently, scientists began attempting de-extinction through cloning and genome editing.
Successful cloning has been performed for many mammals, including the famous Dolly the sheep, though the success rate of the cloning procedure is low3. As traditional cloning involves transplanting the cell nucleus from one organism to a donor egg cell, the resulting organism will have the mitochondrial DNA of the egg donor, and the nuclear DNA of the animal being cloned1. Cloning an extinct species would thus require both a viable cell from the extinct animal and a closely related donor organism to provide an egg and incubate the embryo carrying the DNA. A recent study found that transcription factors, or proteins that can activate specific genes within a cell, can be modified to turn mature cells into synthetic oocytes, or eggs, which could eliminate the need for a donor egg4. With this technology, it is conceivable that frozen cells could be used to bring back an extinct species. The effort to preserve cells from many species is already underway. The San Diego Zoo’s Frozen Zoo has cryopreserved cells from over 1000 species, including the critically endangered northern white rhinoceros (Fig 1B), so that they may be recovered in the future5
Genome editing is another promising way to “bring back” extinct species. The mammoth (Fig 1C) is a well-known example of a species where much of the genome has been sequenced. Due to the close evolutionary relationship between elephants and mammoths there is a possibility of editing an elephant’s genome to get it closer to that of a mammoth. Although gene editing has made many strides with the discovery of CRISPR/Cas9 (see Rebecca Fleeman’s previous LTS article From Changing Your Jeans to Changing Your Genes | Lions Talk Science (lions-talk-science.org)), making multiple edits to a complex organism such as an elephant has proven to be a challenging task5. Genetically modified plants, however, are becoming increasingly common not just to “bring back” species, but to keep species from becoming extinct. For example, researchers have made great strides in creating an American chestnut tree resistant to the blight that essentially wiped out the population6.
Importantly for the case of dinosaur cloning, birds and reptiles, the closest living relatives to the dinosaurs, are especially hard to clone, as they develop in eggs which are difficult to inject with DNA for cloning1. Furthermore, as cloning requires an intact nucleus from the animal to be cloned, this leaves only recently extinct animals, and those that may have remained frozen over the years. However, there is still hope for uncovering the genetic secrets of the dinosaurs. New discoveries and techniques are constantly being identified to study the biological materials left behind by dinosaurs. For example, while DNA degrades quickly, a recent study found that cartilage maintains much of its cellular structure, including potentially fossilized DNA that the authors identified from a Hypacrosaurus7. Another study found that proteins can be identified in well-preserved fossils, giving more insight into how these dinosaurs lived, and adding a crucial layer of information that may one day help bring a dinosaur back to life8.
Should we bring back endangered or extinct species?
Efforts to restore endangered or extinct species have made incredible strides over the past century. For example, samples from the San Diego Zoo’s Frozen Zoo are being used in an effort to bring back the northern white rhinoceros through cloning (Fig 1B).Only two northern white rhinoceros females remain due to poaching and habitat destruction9. While restoring endangered and recently extinct species can help restore the environment that was destroyed by human intervention, species that have been extinct for thousands of years are extinct for a different reason. They lived in a different climate in a different time, and it is hard to predict how they might fit into a modern ecosystem. Is it ethical to bring a living being into the world in which it has no place, or its place is only to be a human attraction (i.e., Jurassic Park)?
Additionally, the scientific strides in cloning and mammalian gene editing could also apply to humans. From helping sterile people have children, to creating “CRISPR babies”, once the technology exists, there will be the potential for use and misuse. Bringing back a dinosaur would be cool, but bringing back a proto-human or Neanderthal seems to cross an ethical line. Though we could learn from these beings, they would have no family history, or none of their own kind to learn from. Furthermore, there is the argument against “playing God” and manually editing organisms to fit the human ideal of what a species should be, rather than focusing on protecting the species that remain in this world.
While I can say with confidence that the chances are low that anyone will be eaten by a dinosaur in the near future, there are always ethical questions that come with any scientific discoveries. Most dinosaurs have been extinct for millions of years, but some species are extinct because humans have disrupted their ecosystems or hunted them to extinction. Is there a point in resurrecting a species that no longer has a habitat to live in? Conversely, could re-introducing a species help restore the delicate ecosystem it was a part of? Importantly, do we as humans have a moral obligation to bring back that which we have destroyed?
TL:DR
- Bringing back extinct species has been attempted through back-breeding, cloning, and gene editing
- With technology quickly improving, de-extinction may become possible
- Just because we can doesn’t mean we should
References
1. Richmond DJ. The potential and pitfalls of de-extinction. Zoologica Scripta. 2016;45(S1):22-36. Epub 27 September 2016. doi: https://doi.org/10.1111/zsc.12212.
2. Heck H. The Breeding-Back of the Aurochs. Oryx. 1951;1(3):117-22. Epub 2009/09/03. doi: 10.1017/S0030605300035286.
3. Alberio R, Wolf E. 25th ANNIVERSARY OF CLONING BY SOMATIC-CELL NUCLEAR TRANSFER: Nuclear transfer and the development of genetically modified/gene edited livestock. Reproduction. 2021;162(1):F59-f68. Epub 20210611. doi: 10.1530/rep-21-0078. PubMed PMID: 34096507; PMCID: PMC8240728.
4. Hamazaki N, Kyogoku H, Araki H, Miura F, Horikawa C, Hamada N, Shimamoto S, Hikabe O, Nakashima K, Kitajima TS, Ito T, Leitch HG, Hayashi K. Reconstitution of the oocyte transcriptional network with transcription factors. Nature. 2021;589(7841):264-9. Epub 20201216. doi: 10.1038/s41586-020-3027-9. PubMed PMID: 33328630.
5. Novak BJ. De-Extinction. Genes (Basel). 2018;9(11). Epub 20181113. doi: 10.3390/genes9110548. PubMed PMID: 30428542; PMCID: PMC6265789.
6. Newhouse AE, Powell WA. Intentional introgression of a blight tolerance transgene to rescue the remnant population of American chestnut. Conservation Science and Practice. 2021;3(4):e348. doi: https://doi.org/10.1111/csp2.348.
7. Bailleul AM, Zheng W, Horner JR, Hall BK, Holliday CM, Schweitzer MH. Evidence of proteins, chromosomes and chemical markers of DNA in exceptionally preserved dinosaur cartilage. Natl Sci Rev. 2020;7(4):815-22. Epub 20200112. doi: 10.1093/nsr/nwz206. PubMed PMID: 34692099; PMCID: PMC8289162.
8. Vogel G. Seeing fossils in a new light. Science. 2019;366(6462):176-8. doi: 10.1126/science.366.6462.176. PubMed PMID: 31601754.
9. Tunstall T, Kock R, Vahala J, Diekhans M, Fiddes I, Armstrong J, Paten B, Ryder OA, Steiner CC. Evaluating recovery potential of the northern white rhinoceros from cryopreserved somatic cells. Genome Res. 2018;28(6):780-8. Epub 20180524. doi: 10.1101/gr.227603.117. PubMed PMID: 29798851; PMCID: PMC5991516.
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