The British Isles have few endemic species due to past frequent glaciations and because of the proximity to Continental Europe and former land bridges which enabled species to re-colonise the islands from the continent following glaciations. Most endemic species to the British Isles are considered to be subspecies of a larger species, with mutations or adaptations slightly changing the species in the islands or in certain localities. Most endemic species or subspecies however date to more recent, post-glacial times, many having spread via land bridges or along the Atlantic seaboard of Europe.