Caves were important refuges for humans and animals that coexisted during the late Pleistocene, the epoch of ice ages that ended 10,000 years ago. These sheltered environments can preserve evidence of extinct biological communities that archaeologists, paleontologists, and geneticists can mine for clues the species' biology, behavior, and evolution. Recently, exceptionally well-preserved bones from European caves have yielded DNA for two Ice Age species, Neanderthals and cave bears. The teams-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 each species. (Most of an individual's DNA is in the nuclei of body cells. The rest is found in the mitochondria, the cell's energy generators.) As technology advances the field of ancient DNA study, more Pleistocene species will be investigated at a genetic level.