It's difficult to imagine that 10,000 years ago, right here in North America, there lived giant animals that are now the stuff of legends - mammoths and mastodons, ground sloths and sabretooth cats. They, and thousands of other species, have vanished from the Earth. And today, partly due to the expansion of one species - ours - animals are going extinct faster than ever before.
The very definition of extinct means gone forever, but what if we could change that? Scientists are making remarkable advances that are bringing us closer than ever before to the possibility of a true animal resurrection.
Who wouldn't be dazzled by an animal like the woolly mammoth, or the sabretooth tiger, the Irish elk or the giant sloth? Today they exist just as bones in museums, alive only in our imaginations and the recreations of artists and filmmakers. But what if that could change?
In the age of DNA, we now know that these vanished creatures, like all life on Earth, are ultimately nothing more than sequences of the four letters - A, C, T, and G - that make up the genetic blueprint or code of life. The codes for extinct animals were thought to have died along with them, until recently, when machines like one at the Smithsonian's DNA lab started working magic.
"Just the study of ancient DNA only broke onto the scene 20 years ago or so. The idea that we could harvest DNA from extinct creatures, from fossil bones, learn something about the past," Sean Carroll, a professor of molecular biology and genetics at the University of Wisconsin, told 60 Minutes correspondent Lesley Stahl.
Carroll says that like so many things in the field of DNA, the progress has been staggering.
One surprising discovery has been the value of ancient hair. Scientists recently discovered that the hair shaft seals DNA inside it like a biological plastic, protecting it, and making hair a rich and plentiful source of genetic information.
"Does that mean that you can take extinct animals, I mean, there's hair in museums? …And get the genetic sequencing?" Stahl asked.
"Possibly, and especially if those animals were preserved in any way, there's a good prospect of that. It's sort of like CSI, you know? How good is this forensic material? Can you get good DNA information from older and older and older material? That's pretty promising," Carroll replied.
So dusty old specimens that have been tucked away in the drawers of natural history museums like the Smithsonian are suddenly potential treasure troves of genetic information: just last year, using only a few clumps of wooly mammoth hair, scientists at Penn State were able to extract enough DNA fragments to figure out most of its genetic sequence, making the woolly mammoth the first extinct animal to have its genome decoded.
Which raises the question of whether resurrecting one of these creatures is really possible.
Scientists say one option would be genetic engineering: take a living animal that's related to the mammoth, like the elephant, figure out all the places where its DNA differs from the mammoth's, and then alter the elephant's DNA to make it match.
That's not possible just yet, but there may be another way: cloning.
"Is it possible that we're gonna get the full DNA of the woolly mammoth and be able to clone it?" Stahl asked.
"Yes, I think we'll be able to get much, if not all, of the woolly mammoth DNA. And the great advantage there is that a lot of the specimens are in permafrost. So they're sorta been conveniently frozen for us, which preserves DNA, preserves tissue better," Carroll said.
But for cloning, just knowing the DNA sequence from hair isn't enough. You'd need an intact mammoth cell, which Carroll says will be difficult to find, but not impossible.