Owing to this struggle, variations, however slight and from whatever cause proceeding, if they be in any degree profitable to the individuals of a species, in their infinitely complex relations to other organic beings and to their physical conditions of life, will tend to the preservation of such individuals, and will generally be inherited by the offspring.
Borroka hau dela eta, aldaketek, txikienak izanik ere eta dena dela haiek sortu dituen kausa, espezie bateko banakoentzat beste izaki organikoekin eta beren bizi-baldintza fisikoekin dituzten erlazio amaigabeki konplexuetarako nolabait baliagarriak baldin badira, banako hauen biziraupenera joko dute eta, eskuarki, ondorengoek heredatuko dituzte.