By Rebecca Jeong

What is De-extinction? 

De-extinction is the process of recreating extinct species using biotechnology. 

People are interested in de-extinction for a variety of reasons, including:

• reintroducing extinct species to restore and improve ecosystems, 
• studying evolutionary biology, by comparing extinct species to existing species that are closely related,
• wildlife tourism

When we think about de-extinction, most people imagine large-sized animals with big teeth and big claws. Especially for wildlife tourism, bigger animals are preferred to entertain the audiences in a zoo. 

How could it be done?

What are some different ways to bring back extinct animals? Some of the approaches that are used to preserve endangered species can also be applied to bringing back extinct animals. 

1. Cloning
   
   Cloning is creating a copy of cells. In other words, using a reference cell (=parent cell) to create a genetically identical cell (=daughter cell). A cell from an extinct species can be retrieved, and then the nuclei of its cells can be implanted into an emptied egg cell of a currently existing species that is genetically related. 
   
   One limitation of this method is that it requires closely-related existing animals. Another limitation is that the genome of extinct animals must have been preserved over time. The genome of extinct animals could be too degraded to use, because the time it takes DNA to break down to 50% of its content (the “half-life”) is 521 years.
   
   
   Celia, whose cells were implanted into surrogates.
   Due to hunting, she was the last animal of her kind (the bucardo).
   Scientists captured her in 1999 and collected her cell tissue.
   The following year, Celia was killed by a falling tree.
   
   In 2003, the first successful de-extinction was done on bucardo (mountain goats that are only found in Pyrenees region). Unfortunately, the animal died 7 minutes after it was born because of a lung defect. The process of bringing 1 bucardo back from extinction was quite challenging. Using the cells from the last living bucardo, the nuclei was implanted in 57 surrogate goats. Out of those, 7 goats got pregnant, and then only 1 bucardo was able to be born. However, this example shows that cloning may be a possible path for de-extinction. 
   
   
2. Genome editing
   
   Genome editing involves recreating extinct species by modifying the genome of a closely-related species, using the extinct species’ genome. Advanced biotechnology such as CRISPR-cas9 could be used.
   
   However, CRISPR may not be able to work at every location of a genome that needs to be edited. In reality, insertion of multiple DNA sequences is a challenging and error-prone process (with only a 0.5 - 20% rate of correct insertion).

What are some limitations of de-extinction?

Although there are many opinions about de-extinction, the most heated argument is whether or not it is ethically right or wrong. 

Because humans have caused many animal extinctions due to hunting and harming habitats through industrialization, does it make sense to bring back extinct animals?  

Here is a list of questions to consider about de-extinction:

Will the de-extinct animal be the same as the original animal, in physiology and behavior?

• Environmental factors, such as temperature and communication among animals, could impact the physical features of the animals. 
• Surrogate animals (closely-related animals that give birth to extinct animals) may influence how the de-extinct animal develops during the early stages of embryo development.
  
  

Will de-extinct animals bring back ancient diseases?

• The de-extinct animal could possibly be a vector of ancient diseases to other species, including humans.
  
  

Will de-extinct animals be able to adapt and survive in the current environment? 

• Since many years have passed by since the animal went extinct, the original ecosystem that extinct animals used to live in does not exist anymore. Other species in the original ecosystem will likely not welcome the de-extinct species when they are first introduced, due to competition for resources. It is likely that it could only be able to live in a man-made habitat.
• De-extinct animals could be more susceptible to modern diseases and parasites.

What is your opinion about de-extinction after reading the blog post? Do you think it should or should not be attempted? 

References

1. https://www.britannica.com/science/de-extinction
2. https://onlinelibrary.wiley.com/doi/full/10.1111/zsc.12212
3. https://www.bbc.com/news/science-environment-25052233 

Illustration "Woolly Mammoth (Mammuthus Primigenius) by Mauricio Anton