But he who will take the trouble to reflect on the steps by which this first degree of sterility could be increased through natural selection to that high degree which is common with so many species, and which is universal with species which have been differentiated to a generic or family rank, will find the subject extraordinarily complex.
Baina gogoeta egiteko lana hartu eta lehen antzutasun maila honetatik, hautespen naturalaren bidez, hainbeste espezierentzat komuna eta genero edo familiatzat sailkatuak izateraino ezberdindu diren espezieetan unibertsala den antzutasun maila garairaino heltzeko behar izan diren urratsei buruz pentsatzen duenak, arrunt korapilatsua eritziko dio gai honi.