Of bears, conservation genetics, and the value of time travel.

P genetics is a historical discipline in the sense that it analyzes the distribution of genetic variants in populations to make inferences about evolutionary processes and events in the past. But it is time trapped, because population geneticists, unlike for example paleontologists or archaeologists, are limited to the analysis of contemporary materials and cannot go back in time to study directly the genetics of previous populations. The enthusiasm for the study of DNA in ancient remains stems partly from the hope that one would be able to overcome this time trap and add a temporal aspect to the study of population genetics (1). Although progress in this direction has been made over the past 10 years, it has often been frustratingly slow. The reason is that very few remains contain retrievable old DNA, and that contamination by modern DNA poses a great problem. As a result, molecular time travel has been achieved only in cases where a single or few representatives of extinct animal species can give insights about their relations with extant species, such as the relationship of the marsupial wolf with extant marsupials (2), moas with extant flightless birds (3), or ground sloths with present-day sloths (4). In contrast, diachronical population studies have been limited to the last 100 years from which voucher specimens exist in zoological museums (e.g., ref. 5). Now, Leonard et al. (6) present a study where population genetics is taken further back in time—to brown bears preserved since the last glaciation in the permafrost of Alaska and Northern Canada. Their results provide insights about the history of bears and are provocative in their implications for conservation genetics.