-But some scientists believe species revival will never happen because both methods are problematic. One of the major challenges is how to obtain enough high-quality DNA from an extinct species to conduct an experiment. While it is theoretically possible under idea conditions to preserve genetic material for thousands of years, these conditions rarely occur in real life. For example, researchers have obtained a number of samples of mammoth DNA, but none have been usable. And the cloning process presents its own problems. Scientists have been able to clone only a few species of animals, and more cloned creatures are frail and don't live very long.