We have differences correlated not only with one sex, but with that short period when the reproductive system is active, as in the nuptial plumage of many birds, and in the hooked jaws of the male salmon.
Sexu batekin ezezik, ugal-aparatua ihardunean ari den aldi laburrarekin ere korrelazionaturik dauden ezberdintasunak ditugu, txori askoren ezkon-lumaian eta izokin arraren gakodun barailetan ageri direnak bezalakoak.