Donders Wonders Blog

Can we resurrect extinct animals?

This post is also available in Dutch.

Mass extinction is at Earth’s doorstep. Can we somehow turn back time? What if extinction wasn’t permanent? De-extinction, resurrection biology, species revivalism—or however you refer to it—could be the key to breathing life back into our planet’s ecology. How does it work?

Animal species are going extinct at a rate faster than ever — largely because of human-related activities. Humans drive animals out of their natural habitats in order to use land for housing and agriculture. People also hunt and fish, sometimes to a point where the last individual of a species disappears from the face of the Earth. This happened to the passenger pigeon, whose last member died in 1914. It turns out that passenger pigeons were so delicious that people hunted them until there were none left. If we make species vanish, can we also bring them back to life? Is de-extinction possible?

What is de-extinction?

The movement of de-extinction first received a lot of media attention in 2013 with the TEDxDeExtinction event organized by Revive & Restore, a USA-based non-profit organization. The main idea behind this movement is the reintroduction of an extinct species into its former habitat. De-extinction is possible through three methods: cloning, gene editing and selective breeding. The first two are new technologies while selective breeding is what humans have used for thousands of years (i.e., when we select a pair of individuals with specific characteristics and breed them). 

Old technology: Selective breeding

A successful case of how a type of selective breeding, like back-breeding, can help revive a species is the auroch, the ancestor of all domesticated cattle. Once prevalent all across Europe, the auroch was hunted to its extinction in 1627. Luckily, strands of its DNA remained scattered in various cattle breeds. Scientists first sequenced the genome of the auroch, then specific cattle species were bred together to produce offspring closer to the qualities of the original auroch, and finally the offspring were bred together. Several generations of aurochs need to be bred in order to get to the closest possible outcome and efforts have been successful so far.

New technologies: Cloning and gene editing

Can we revive long-extinct species like the woolly mammoth that went extinct 4,000 years ago? In theory, we can do so by using cloning or gene editing. In the first case, a living cell of a mammoth is necessary because of how cloning works: a nucleus of a somatic (body) cell is inserted into an egg cell that has had its own nucleus removed. Then, the egg is stimulated with a mild electrical current and begins dividing, after which, it can be implanted into a womb, real or artificial. As of now, cloning a mammoth is a far-fetched option. However, earlier this year, scientists succeeded in taking nucleus-like structures from a well-preserved mammoth and implanting them into mouse oocytes (i.e., immature egg cells). Efforts to stimulate cell division into mammoth cells have not been fruitful yet, though.

A more viable option in reviving a woolly mammoth is to rely on gene editing, the result of which, crudely put, would be an elephant and a mammoth hybrid. The closest living relative, the Asian elephant, looks quite different from the woolly mammoth. Yet, geneticists believe that transforming an Asian elephant into a woolly mammoth can be achieved through genome editing using a technique called CRISPR/cas9. Invented in 2012, this technique allows for the alteration of any living organism’s genome through deletion or addition of genes with very high precision. Despite the efficiency of introducing genetic changes using CRISPR/cas9, turning an Asian elephant into a woolly mammoth is no trivial task. Geneticists have estimated that the two species have 1.5 million nucleotide-level differences. On top of this, there are always ethical questions. The Asian elephant itself is an endangered species so it needs protection. Would we be willing to use an animal species in decline as the maternal host for the woolly mammoth?

This time, I will leave the ethical considerations aside as those would need a blog post of their own. What is important, though, is that scientific progress of the past decades now allows for something previously unimaginable: bringing an extinct species back to life. Now, it is up to the scientific community and all interested parties to decide how to use these new technologies wisely.

Original language: English

Author: Julija Vaitonyte
Buddy: Christienne Gonzales Damatac
Editor: Mónica Wagner
Translator: Wessel Hieselaar
Editor Translation: Jill Naaijen
Featured image by Stefan Keller via Pixabay (license)

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