Again, an organ, useful under certain conditions, might become injurious under others, as with the wings of beetles living on small and exposed islands; and in this case natural selection will have aided in reducing the organ, until it was rendered harmless and rudimentary.
Gainera, egoera batzuetan baliagarria den organoa kaltegarri bihur daiteke bestelako egoeretan, irla txikietan eta haize afrontuan bizi diren kakarraldoen hegoen kasuan, esate baterako; eta kasu honetan hautespen naturalak lagunduko zuen organoa murrizten, kaltegabeko eta aztarna-organo bilakatzeraino.