It would at first lead by slow steps to the more and more complete reduction of a part, until at last it became rudimentary-as in the case of the eyes of animals inhabiting dark caverns, and of the wings of birds inhabiting oceanic islands, which have seldom been forced by beasts of prey to take flight, and have ultimately lost the power of flying.
Lehenbizi atal jakin baten gero eta murrizte handiagora eramanen luke poliki-poliki, atal hori azkenean aztarna bilakatu arte; hauxe da haitzulo ilunetan bizi den zenbait animaliaren begien kasua eta irla ozeanikoetan bizi den zenbait hegaztiren hegoen kasua, harrapariek inoiz gutxitan hegaz eragin dietenez, azkenean hegaz egiteko ahalmena galdu duten hegaztiena.