He who is able to explain why the elephant, and a multitude of other animals, are incapable of breeding when kept under only partial confinement in their native country, will be able to explain the primary cause of hybrids being so generally sterile.
Elefantea eta beste makina bat animalia, beren sorterrian, aldez bada ere, hesiperatzen direnean, umatzeko ezgai zergatik diren azaldu ahal duenak, hibridoak hain orokorki antzuak izatearen oinarrizko zergatia ere azaldu ahal izanen du.