Animals that are extinct can come back from extinction.
True
False

(False) because Earth is in the midst of its sixth mass extinction: Somewhere between 30 and 159 species disappear every day, thanks largely to humans, and more than 300 types of mammals, birds, reptiles, and amphibians have vanished since 1500. These rates do not bode well for the future of life on our planet, but what if extinction wasn’t permanent? What if we could resurrect some of the species we’ve lost?

For decades the notion of “de-extinction” hovered on the scientific fringes, but new advances in genetic engineering, especially the CRISPR-Cas9 revolution, have researchers believing that it’s time to start thinking seriously about which animals we might be able to bring back, and which ones would do the most good for the ecosystems they left behind. Indeed, earlier this month, ecologists at the University of California, Santa Barbara (UCSB), published guidelines for how to choose which species to revive if we want to do the most good for our planet's ecosystems.

The two animals at the forefront of this discussion are the woolly mammoth, a hairy, close relative of the elephant that lived in the Arctic, and the passenger pigeon, a small, gray bird with a pinkish red breast once extremely common in North America. The last mammoths died about 4000 years ago, and the passenger pigeon vanished around 1900. Research on reviving both species is well underway, and scientists close to the field think de-extinction for these animals is now a matter of “when,” not “if.”