Around 10,000 years ago, in the region of the United States now known as the Appalachians, lived one of the most impressive mammals ever to inhabit North American. With a height of over 8 feet, and weighing up to 800 pounds, the giant ground sloth ( Megalonyx jeffersonii to scientists) was a formidable sight. However, the ground sloth, like most large land mammals in North America, went extinct. Why is still a mystery to scientists - some believe that it may have been the result of a change in climate, others suggest that it may have been from predation by humans.

Such is the case for many species, and it is the basis of Darwinian natural selection. Those species that have the genetic variation to adapt to a changing environment do, and those that do not go extinct. Unfortunately, humans have been changing the environment a little faster than most species would like. Many ecologists and biodiversity experts believe that we are experiencing a mass extinction event unlike any in the past 65 million years. And, until recently, we had few choices to prevent the extinction of a species - we could either put it in a zoo, or try to conserve its natural habitat. While both have had some success, most of the news from the conservation front is not good.

Some have asked whether it may be possible to clone extinct animals using the DNA from frozen
tissues. Until recently, the majority of attempts to do this have failed - mostly because the DNA was damaged by the process of freezing. DNA is a durable, but also delicate, molecule. Its structure protects
it for long periods of time, but even slight damage to its information-containing bases can be troublesome. That may have changed with a discovery by Teruhiko Wakayama, a Japanese developmental biologist. Wakayama has found a way to use frozen DNA in a cloning process (see the PNAS paper here). His process appears to reduce the influence of damaged DNA, allowing previously unsuitable tissues to be
used in the cloning process. Once a cell line is cloned, it could be used to revive an extinct species.

For the ground sloth, passenger pigeon, and the dodo bird, this may be the resurrection that
the species needed. Not only could we finally right a terrible wrong in our human history, we may be able to prevent (or at least postpone) the extinction of some species that are currently struggling for survival.
Of course, no one is actually (yet) suggesting that we can bring back a giant sloth, but if we can perfect the process, then someday hikers along the Appalachian Trail may have more to deal with than just brown bears.

Additional References:

Wakayama's 2008 paper in PNAS