It is most difficult always to remember that the increase of every living creature is constantly being checked by unperceived hostile agencies; and that these same unperceived agencies are amply sufficient to cause rarity, and finally extinction.
Oso zaila da beti gogoratzea hantxe ari direla eragile etsai ezezagunak etengabe ekin eta ekin bizidun ororen gehikuntza galarazten, eta eragile ezezagun horiek aski eta gehiegi direla bakantasuna eta, azkenean, iraungipena eragiteko.