When a young naturalist commences the study of a group of organisms quite unknown to him he is at first much perplexed in determining what differences to consider as specific and what as varietal; for he knows nothing of the amount and kind of variation to which the group is subject; and this shows, at least, how very generally there is some variation.
Naturalista gazte bat erabat ezezaguna duen organismo talde bat aztertzen hasten denean, zeharo duda-mudatan ibiltzen da espezieari zeintzuk alde dagozkion eta zeintzuk aldakiari erabakitzeko orduan, inola ere ez baitaki talde hori zenbat eta nolako aldakuntzen mende dagoen; eta honek agerian jartzen du, gutxienez, aldakuntza mailaren batean zein maiz gertatzen den.