New species are formed by having some advantage over older forms; and the forms, which are already dominant, or have some advantage over the other forms in their own country, give birth to the greatest number of new varieties or incipient species.
Espezie berriak forma zaharrekiko abantailaren bat dutelako sortzen dira; eta jada nagusi diren formek, edo herrialde berean bizi diren beste formekiko abantailaren bat dutenek, aldaki edo espezie hasberri gehienak sortzen dituzte.