How do you de-extinct an animal?
There are three main approaches to de-extinction scientists talk about. The first, called backbreeding, involves finding living species that have traits similar to the extinct species. Then scientists would selectively breed these animals to try to make a version that more closely resembles the extinct animal—a process already underway for some extinct species like aurochs. This isn’t really a true de-extinction, but it might still let us fill in missing ecological functions. In the case of mammoths, scientists might try to mate Asian elephants with more body hair than usual, for example.
A second option is cloning. Scientists would take a preserved cell from a recently extinct animal (ideally before the last of its kind died) and extract the nucleus. They would then swap this nucleus into an egg cell from the animal’s closest living relative and implant the egg into a surrogate host. (Researchers actually did this in 2007, and a common goat gave birth to an extinct species, the Pyrenean ibex. The infant lived only 7 minutes however, because of genetic problems with its lungs.) Cloning may eventually give us basically identical genetic copies of extinct species, but we’ll be restricted to animals that went extinct more recently and have well-preserved cells with intact nuclei. The mammoth and the passenger pigeon may never be cloned.
The newest option is genetic engineering. Here, researchers would line up the genome of an extinct animal with that of its closest living relative. They would then use CRISPR and other gene-editing tools to swap relevant genes from the extinct animal into the living species and implant the hybrid genome into a surrogate (or grow it in an artificial womb). This approach doesn’t produce genetically identical copies of extinct animals, but rather modern versions of an animal engineered to look and behave like its extinct relatives. This is the technology being used by the mammoth and passenger pigeon groups.