As the individuals of the same species come in all respects into the closest competition with each other, the struggle will generally be most severe between them; it will be almost equally severe between the varieties of the same species, and next in severity between the species of the same genus.
Espezie bereko animaliak edozertan elkarrekin lehiarik bizienean ihardun beharrean gertatzen direnez gero, haien artean borrokarik gogorrena izanen da; ia hauena bezain gogorra izanen da espezie bereko aldakien artekoa, eta hurrengo gogorrena genero bereko espezieen artekoa.