Even on a wide area, which has during a long period remained continuous, and of which the climatic and other conditions of life change insensibly in proceeding from a district occupied by one species into another district occupied by a closely allied species, we have no just right to expect often to find intermediate varieties in the intermediate zones.
Aldi oso luzean etengabe iraun duen eta, espezie bat bizi den barrutitik beste oso hurbil bat bizi denera pasatzean, klima eta beste bizi-baldintza batzuk sentitzeke aldatzen diren herrialde oso handi batean bertan ere, ezin dugu arrazoiz espero bitarteko aldeetan bitarteko aldakiak sarri aurkitzerik.