Whatever the cause may be of the variability of secondary sexual characters, as they are highly variable, sexual selection will have had a wide scope for action, and may thus have succeeded in giving to the species of the same group a greater amount of difference in these than in other respects.
Ezaugarri sexual sekundarioen aldagarritasunaren kausa zeinahi delarik ere, oso aldagarriak direnez gero, hautespen sexualak ihardun-eremu zabala eduki behar izan du, eta horrela talde bereko espezieei ezaugarri hauetan besteetan baino ezberdintasun handiagoa eman ahal izan die.