[lemma=□]
[lemma=species]
If the existence of the same species at distant and isolated points of the earth 's surface can in many instances be explained on the view of each species having migrated from a single birthplace ; then , considering our ignorance with respect to former climatical and geographical changes , and to the various occasional means of transport , the belief that a single birthplace is the law seems to me incomparably the safest . Hence it is by no means surprising that one species should retain the same identical form much longer than others ; or , if changing , should change in a less degree . Lesson in which students identify several species of marine animals hat might become stranded , distinguish the animals ? Similar work on minnows of the genus Campostoma ( stonerollers ) from the eastern and southeastern United States and Mexico indicates that mtDNA haplotypes in the two most widespread species ( C. anomalum and C. oligolepis ) are structured geographically , rather than phylogenetically , indicating that both " species " are composites of multiple independent lineages .