In such cases, slight modifications, which in any way favoured the individuals of any species, by better adapting them to their altered conditions, would tend to be preserved; and natural selection would have free scope for the work of improvement.
Kasu hauetan, espezie bateko banakoentzat ezertarako mesedegarri ez diren aldaketa txikiek irauteko joera izanen lukete, aldaturiko baldintzetara hobeto moldatzeko, eta hautespen naturalak eremu librea luke hobekuntza lanerako.