by Sabrina Imbler (NYT NEWS SERVICE) .- More than a century ago, a bluish butterfly flitted among the sand dunes of the Sunset District in San Francisco and laid its eggs on a plant known as deerweed. As the citys development overtook the dunes and deerweed, the butterflies vanished, too. The last Xerces blue butterfly was collected in 1941 from Lobos Creek by an entomologist who would later lament that he had killed what was one of the last living members of the species. But was this butterfly truly a unique species? Scientists could all agree that the grim fate of the Xerces blue the first butterfly known to go extinct in North America because of human activities was a loss for biodiversity. But they were divided over whether Xerces was its own distinct species, a subspecies of the widespread silvery blue butterfly Glaucopsyche lygdamus, or even just an isolated population of silvery blues. This may seem a scientific quibble, but if Xerces blue was not in fact a genetically distinct lineage, it would no ... More