Researchers have unraveled the genetic code of a wild horse that loped across the frozen Yukon about 700,000 years ago, making it the oldest creature by far to reveal its DNA to modern science. 
 
 Until recently, experts believed it was impossible to recover useful amounts of DNA from fossils that old. The previous record holder for oldest genome belonged to a polar bear that lived more than 110,000 years ago. The horse sequence, described Wednesday in the journal Nature, amounts to a dramatic increase in how far back scientists can peer into the biochemical history of advanced life. 
 
 The DNA was extracted from a 6-inch slice of a fossilized horse leg bone that was found nine years ago. Under normal conditions, DNA begins to degrade soon after death. But this bone was preserved in permafrost at Thistle Creek in Canada's Yukon Territory. 
 
 Dating techniques revealed that the animal lived in an epoch when woolly mammoths, saber-toothed cats and giant beavers shared turf with ancestral humans. 
 
 The work "opens great perspectives as to the level of details we can reconstruct of our origins and the evolutionary history of every animal on the planet," said study leader Ludovic Orlando of the Center for GeoGenetics at the Natural History Museum of Denmark. 
 
 Orlando and an international team of collaborators pieced together even the tiniest of DNA fragments recovered from the bone. Such genetic puzzle assembly generally includes multiple samples from each part of the genome, sometimes as many as five or 10. In this case, the so-called coverage was just 1.12. 
 
 That's not enough detail to say much about what the horse looked like, said Eske Willerslev, an evolutionary biologist at the Natural History Museum of Denmark who worked on the study. Team members suggested the horse was about the size of a modern Icelandic or Arabian horse, though it probably was less muscular, and perhaps slower. 
 
 "If they were fast runners, it was not because of the same genes we know of today," Orlando said. 
 
 As part of the genetic sleuthing, the team also sequenced the DNA of a 43,000-year-old horse fossil, five modern domesticated horses, a wild Przewalski's horse native to the Mongolian steppes, and a donkey from the Copenhagen Zoo named Willy. 
 
 By comparing all of these genomes, the researchers determined that the most recent common ancestor of all these species — as well as zebras — lived 4 million to 4.5 million years ago. That's about 2 million years earlier than previously thought, and allows for far more time for horses to have evolved into the animals we know today. 
 
 The findings offered a window into 29 regions of the domestic horse's genome that differed from that of the wild Przewalski's horse, suggesting these changes were part of their evolutionary path toward domestication. Some of those changes involved the immune and olfactory systems. 
 
 The analysis also offers hope for the fate of the Przewalski's horse, an endangered animal whose DNA showed no signs of interbreeding with modern horses. 
 
 "It is 100% wild," Willerslev said. "There is no domestic genetics present in that horse. Which of course suggests these guys are really worth preserving." 
 
 The DNA analysis revealed that the species has enough genetic variety to enable it to recover if conservation efforts can be sustained. Once considered extinct in the wild, the horse was reintroduced to the Mongolian steppes in 1985. 
 
 Other scientists who specialize in sequencing ancient DNA praised the work on the Canadian horse. But they cautioned that it wouldn't help them decode the DNA of human ancestors who lived so long ago. 
 
 "We've known for a long time now that DNA preservation is exceptionally good in permafrost compared to other environments," said Mark Stoneking, a geneticist at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, who was not involved in the study. "Unfortunately, with the exception of Otzi the Iceman, none of our ancestors have been so obliging as to die under circumstances where the remains are frozen soon after death and remain frozen until discovery." 
 
 Paleogeneticist Carles Lalueza-Fox of the Institute of Evolutionary Biology in Barcelona, Spain, who has studied the Neanderthal genome, was also pessimistic: "We are not going to find very ancient humans preserved in permafrost." ||||| Author notes 
 
 Ludovic Orlando 
 
 , Aurélien Ginolhac 
 
 & Guojie Zhang These authors contributed equally to this work. Damian Szklarczyk 
 
 & Jakob Vinther Present addresses: Bioinformatics Group, Institute of Molecular Life Sciences, University of Zurich, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland (D.S.); Departments of Earth Sciences and Biological Sciences, University of Bristol BS8 1UG, UK (Ja.V.). 
 
 Affiliations 
 
 Centre for GeoGenetics, Natural History Museum of Denmark, University of Copenhagen, Øster Voldgade 5–7, 1350 Copenhagen K, Denmark Ludovic Orlando 
 
 , Aurélien Ginolhac 
 
 , Mikkel Schubert 
 
 , Enrico Cappellini 
 
 , Julia T. Vilstrup 
 
 , Maanasa Raghavan 
 
 , Thorfinn Korneliussen 
 
 , Anna-Sapfo Malaspinas 
 
 , Jesper Stenderup 
 
 , Amhed M. V. Velazquez 
 
 , Morten Rasmussen 
 
 , Andaine Seguin-Orlando 
 
 , Cecilie Mortensen 
 
 , Kim Magnussen 
 
 , Kristian Gregersen 
 
 , Anders Krogh 
 
 , M. Thomas P. Gilbert 
 
 , Kurt Kjær 
 
 & Eske Willerslev Shenzhen Key Laboratory of Transomics Biotechnologies, BGI-Shenzhen, Shenzhen 518083, China Guojie Zhang 
 
 , Xiaoli Wang 
 
 , Jiumeng Min 
 
 & Jun Wang Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta T6G 2E3, Canada Duane Froese The Bioinformatics Centre, Department of Biology, University of Copenhagen, Ole Maaløes Vej 5, 2200 Copenhagen, Denmark Anders Albrechtsen 
 
 , Ida Moltke 
 
 & Anders Krogh Department of Ecology and Evolutionary Biology, University of California, Santa Cruz, California 95064, USA Mathias Stiller 
 
 , James Cahill 
 
 & Beth Shapiro Center for Biological Sequence Analysis, Department of Systems Biology, Technical University of Denmark, DK-2800 Lyngby, Denmark Bent Petersen 
 
 , Josef Vogt 
 
 , Søren Brunak 
 
 & Thomas Sicheritz-Ponten Department of Human Genetics, The University of Chicago, Chicago, Illinois 60637, USA Ida Moltke Department of Biology, Emory University, Atlanta, Georgia 30322, USA Philip L. F. Johnson Department of Integrative Biology, University of California, Berkeley, California 94720, USA Matteo Fumagalli Novo Nordisk Foundation Center for Protein Research, Faculty of Health and Medical Sciences, University of Copenhagen, Blegdamsvej 3b, 2200 Copenhagen, Denmark Damian Szklarczyk 
 
 , Christian D. Kelstrup 
 
 , Lars Juhl Jensen 
 
 & Jesper V. Olsen Jackson School of Geosciences, The University of Texas at Austin, 1 University Road, Austin, Texas 78712, USA Jakob Vinther Texas Materials Institute, The University of Texas at Austin, Austin, Texas 78712, USA Andrei Dolocan Government of Yukon, Department of Tourism and Culture, Yukon Palaeontology Program, PO Box 2703 L2A, Whitehorse, Yukon Territory Y1A 2C6, Canada Grant D. Zazula Danish National High-throughput DNA Sequencing Centre, University of Copenhagen, Øster Farimagsgade 2D, 1353 Copenhagen K, Denmark Andaine Seguin-Orlando 
 
 , Cecilie Mortensen 
 
 & Kim Magnussen NABsys Inc, 60 Clifford Street, Providence, Rhode Island 02903, USA John F. Thompson Archeology, University of Southampton, Avenue Campus, Highfield, Southampton SO17 1BF, UK Jacobo Weinstock Zoological Museum, Natural History Museum of Denmark, University of Copenhagen, Universitetsparken 15, 2100 Copenhagen, Denmark Kristian Gregersen Department of Basic Sciences and Aquatic Medicine, Norwegian School of Veterinary Science, Box 8146 Dep, N-0033 Oslo, Norway Knut H. Røed Département histoire de la Terre, UMR 5143 du CNRS, paléobiodiversité et paléoenvironnements, MNHN, CP 38, 8, rue Buffon, 75005 Paris, France Véra Eisenmann Science for Life Laboratory, Department of Medical Biochemistry and Microbiology, Uppsala University, SE-751 23 Uppsala, Sweden Carl J. Rubin 
 
 & Leif Andersson Baker Institute for Animal Health, Cornell University, Ithaca, New York 14853, USA Donald C. Miller 
 
 & Douglas F. Antczak Center for Zoo and Wild Animal Health, Copenhagen Zoo, 2000 Frederiksberg, Denmark Mads F. Bertelsen Novo Nordisk Foundation Center for Biosustainability, Technical University of Denmark, DK-2970 Hørsholm, Denmark Søren Brunak 
 
 & Thomas Sicheritz-Ponten Zoology Department, College of Science, King Saud University, Riyadh 11451, Saudi Arabia Khaled A. S. Al-Rasheid San Diego Zoo’s Institute for Conservation Research, Escondido, California 92027, USA Oliver Ryder Department of Biology, University of Copenhagen, Ole Maaløes Vej 5, 2200 Copenhagen, Denmark John Mundy 
 
 & Jun Wang Department of Biology, The University of York, Wentworth Way, Heslington, York YO10 5DD, UK Michael Hofreiter Departments of Integrative Biology and Statistics, University of California, Berkeley, Berkeley, California 94720, USA Rasmus Nielsen King Abdulaziz University, Jeddah 21589, Saudi Arabia Jun Wang Macau University of Science and Technology, Avenida Wai long, Taipa, Macau 999078, China Jun Wang 
 
 Contributions 
 
 L.O. and E.W. initially conceived and headed the project; G.Z. and Ju.W. headed research at BGI; L.O. and E.W. designed the experimental research project set-up, with input from B.S. and R.N.; D.F. and G.D.Z. provided the Thistle Creek specimen, stratigraphic context and morphological information, with input from K.K.; K.H.R., B.S., K.G., D.C.M., D.F.A., K.A.S.A.-R. and M.F.B. provided samples; L.O., J.T.V., Ma.R., M.H., C.M. and J.S. did ancient and modern DNA extractions and constructed Illumina DNA libraries for shotgun sequencing; Ja.W. did the independent replication in Oxford; Ma.S. did ancient DNA extractions and generated target enrichment sequence data; Ji.M. and X.W. did Illumina libraries on donkey extracts; K.M., C.M. and A.S.-O. performed Illumina sequencing for the Middle Pleistocene and the 43-kyr-old horse genomes, the five domestic horse genomes and the Przewalski’s horse genome at Copenhagen, with input from Mo.R.; Ji.M. and X.W. performed Illumina sequencing for the Middle Pleistocene and the donkey genomes at BGI; J.F.T. headed true Single DNA Molecule Sequencing of the Middle Pleistocene genome; A.G., B.P. and Mi.S. did the mapping analyses and generated genome alignments, with input from L.O. and A.K.; Jo.V. and T.S.-P. did the metagenomic analyses, with input from A.G., B.P., S.B. and L.O.; Jo.V. and T.S.-P. did the ab initio prediction of the donkey genes and the identification of the Y chromosome scaffolds, with input from A.G. and Mi.S.; L.O., A.G. and P.L.F.J. did the damage analyses, with input from I.M.; A.G. did the functional SNP assignment; A.M.V.V. and L.O. did the PCA analyses, with input from O.R.; B.S. did the phylogenetic and Bayesian skyline reconstructions on mitochondrial data; Mi.S. did the phylogenetic and divergence dating based on nuclear data, with input from L.O.; A.G. did the PSMC analyses using data generated by C.J.R. and L.A.; L.O. and A.G. did the population divergence analyses, with input from J.C., R.N. and M.F.; L.O., A.G. and T.K. did the selection scans, with input from A.-S.M. and R.N.; A.A., I.M. and M.F. did the admixture analyses, with input from R.N.; L.O. and A.G. did the analysis of paralogues and structural variation; Ja.V. and A.D. did the amino-acid composition analyses; E.C., C.D.K., D.S., L.J.J. and J.V.O. did the proteomic analyses, with input from M.T.P.G. and A.M.V.V.; L.O. and V.E. performed the morphological analyses, with input from D.F. and G.D.Z.; L.O. and E.W. wrote the manuscript, with critical input from M.H., B.S., Jo.M. and all remaining authors. 
 
 Competing interests 
 
 The authors declare no competing financial interests. 
 
 Corresponding authors 
 
 Correspondence to Ludovic Orlando or Jun Wang or Eske Willerslev.
– Woolly mammoths, saber-toothed tigers, and... horses? According to research using the oldest DNA ever found, horses have been trotting around for millions of years—about 4 million, to be exact. The study, published in Nature, explains how scientists used DNA from a 700,000-year-old horse foot bone found in Canada's Arctic to compare ancient and modern species. What they discovered were exceptional details that dated horse evolution back 2 million years further than previously thought, proving the majestic animals kept some intimidating company. Scientists argue that the bone's discovery in permafrost—which slows DNA decay—has opened doors to how far back they can look. (Before the find, the oldest DNA came from a polar bear that lived more than 110,000 years ago.) It offers "great perspectives as to the level of details we can reconstruct of our origins and the evolutionary history of every animal on the planet," the study lead tells the LA Times. Unfortunately for our own species, says one geneticist, "with the exception of Otzi the Iceman, none of our ancestors have been so obliging as to die under circumstances where the remains are frozen soon after death and remain frozen until discovery."