As we see that those variations which, under domestication, appear at any particular period of life, tend to reappear in the offspring at the same period; for instance, in the shape, size and flavour of the seeds of the many varieties of our culinary and agricultural plants; in the caterpillar and cocoon stages of the varieties of the silkworm; in the eggs of poultry, and in the colour of the down of their chickens; in the horns of our sheep and cattle when nearly adult; so in a state of nature natural selection will be enabled to act on and modify organic beings at any age, by the accumulation of variations profitable at that age, and by their inheritance at a corresponding age.
Etxe-egoeran bizitzako aldi jakin batean agertzen diren aldakuntzak aldi bertsuan ondorengoengan berragertzeko joera dutela ikusten dugun bezala,-esate baterako, honako hauetan agertzen direnak, alegia, gure soro eta baratze-landereen aldaki ugarien hazien forma, tamainu eta zaporean, zetarraren beldar eta zibot egoeran, barru-hegaztien arrautzetan eta haien txitoen biloxkaren kolorean, ardien eta abelgorriaren adarretan ia guztiz haziak direnean-, halaxe natur egoeran ere hautespen naturalak ihardun ahal izanen du izaki organikoengan eta edozein adinetan aldarazi, adin horretarako onuragarri diren aldakuntzen metaketaz eta, dagokion adinean, herentziaz.