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<br />decisions will be made to assure either survival of the subspecies, restoration of the habitat, or <br />recovery for both. <br /> <br />ORIGINS AND TAXONOMIC THEORY <br /> <br />While it is not the intent of this HCA to provide detailed documentation of phylogeny and prehistoric <br />zoogeography of these cutthroat trout, it is important to review the theory represented in the <br />most recent work on native western trout (Behnke 1992). For an indepth discussion on the genesis <br />of the native western trout, the reader should refer directly to Behnke's monograph. Phylogenetic <br />and zoogeography theory supports the concept that, while evolutionary sequences leading to <br />present cutthroat trout species and subspecies originated in the mid-Pleistocene era (more than <br />one million years ago), most historical and prehistorical distributions were determined by events <br />occurring in the last glacial and post-glacial periods (about 70,000 years ago to the present, <br />Behnke 1992). For the purpose of this assessment, reference to the prehistoric status addresses <br />conditions existing before the presence of white explorers (prior to 1800 AD) within the cutthroat <br />distributional area (Figure 1). Reference to the historic status addresses conditions occurring <br />during and subsequent to the exploration and settlement of the western Rocky Mountains by <br />early white explorers (after 1800 AD). <br /> <br />viii <br />