This difficulty, as in the case of unconscious selection by man, is avoided on the theory of gradual evolution, through the preservation of a large number of individuals, which varied more or less in any favourable direction, and of the destruction of a large number which varied in an opposite manner.
Zailtasun hau, gizakiak eginiko hautespen inkontzientearen kasuan bezala, ekidin egiten da mailakako eboluzioaren teoriaren arabera, edonolako norabide mesedegarrian aldaturiko banako askoren kontserbazioaren eta alderantziz aldaturiko askoren suntsipenaren bidez.