Instances could be given of similar varieties being produced from the same species under external conditions of life as different as can well be conceived; and, on the other hand, of dissimilar varieties being produced under apparently the same external conditions.
Espezie berengandik pentsa litezkeen bizi-baldintza ezberdin guztien pean sorturiko antzeko aldakien adibideak jar litezke; eta, aitzitik, itxuraz kanpo-baldintza beretan sorturiko aldaki ezberdinenak ere.