It's estimated 20 percent of species on Earth currently face extinction, and by the end of the century, that number could up to 50 percent.
There are several ways to resurrect a species. Scientists can use back-breeding, a technique that involves breeding animals to develop the genetic traits in their extinct relatives.
Other researchers might opt for cloning — taking a cell nucleus from an extinct species and putting it into a related host — or just manipulating an existing animal's genes.
But because de-extinction efforts are relatively new, there's a lot of disagreement over if it's a good idea.