Disuse, aided sometimes by natural selection, will often have reduced organs when rendered useless under changed habits or conditions of life; and we can understand on this view the meaning of rudimentary organs.
Erabilerarik ezak, hautespen naturalaren laguntzaz batzuetan, azturak edo bizi-baldintzak aldatzean emendiorik gabeko bihurturiko organoak txikiagotu eginen zituen maiz; eta, ikuspegi honen arabera, ulertu ahal dugu aztarna-organoen esangura.