| old mice, young islands and competing biogeographical hypotheses. | naturally occurring variation within a small rodent species native to the southeastern usa, peromyscus polionotus, has interested biologists for nearly a century. this species has contributed significantly to our understanding of geographical variation and has often been presented as an example of adaptive evolution. much of the interest in this organism has been predicated on assumptions that the species is relatively young (<300 000 bp) and that coastal populations have a very recent history ( ... | 2007 | 17956552 |