Scientists have traditionally looked to fossil evidence of extinct species to understand how Earth’s plant and animal life evolved from ancestral forms. By comparing the body structures of species past and present, they can construct family trees that represent change over time. In recent decades, DNA analysis has emerged as another powerful tool to decipher evolutionary relationships. So far, fragments of DNA from about 50 extinct species have been extracted from body parts preserved in permafrost, ancient bones preserved in caves, and other remains. Once the units of DNA in the fragments are sequenced and arranged in their original order, scientists can compare the genetic blueprints of extinct species to those alive today to calculate the degree of relatedness between them and learn when key evolutionary changes arose.
Recently, two groups of scientists—one led by researchers at Germany’s Max Planck Institute for Evolutionary Anthropology, and the other from the Physiogenomics Laboratory at the French Atomic Energy Commission—decoded the complete sequence of mitochondrial DNA for the cave bear, a species that became extinct at the end of the last ice age 10,000 years ago. (Mitochondrial DNA is the kind of DNA found in the mitochondria, the cell’s energy generators. Most of an individual’s DNA is nuclear DNA, which is packaged inside the nuclei of cells.) The DNA evidence allowed the teams to confirm that the cave bear’s closest living relatives are the polar bear and the brown bear. The Max Planck team also decoded DNA from another extinct bear species, the American giant short-faced bear. By understanding the genetics of these extinct species, the researchers were able to sort out the bear family tree with a precision that could not be achieved with fossil evidence alone.