It must, however, be owned that we cannot understand, on the above or any other view, several facts with respect to the sterility of hybrids; for instance, the unequal fertility of hybrids produced from reciprocal crosses; or the increased sterility in those hybrids which occasionally and exceptionally resemble closely either pure parent.
Aitortu beharra dugu, hala ere, ez dugula, ez arestian aipaturiko teoriaz ez beste ezeinez, hibridoen antzutasunarekin loturiko zenbait egitate ulertzerik; esate baterako, elkarrekiko gurutzaketez sorturiko hibridoen ugalkortasun desberdina; edo lantzean behin eta salbuespenez guraso garbi bataren edo bestearen antz handia duten hibridoek ugalkortasun handiagoa izatea.