All being mainly due to the species of the same group being the descendants of a common progenitor, from whom they have inherited much in common, to parts which have recently and largely varied being more likely still to go on varying than parts which have long been inherited and have not varied, to natural selection having more or less completely, according to the lapse of time, overmastered the tendency to reversion and to further variability, to sexual selection being less rigid than ordinary selection, and to variations in the same parts having been accumulated by natural and sexual selection, and thus having been adapted for secondary sexual, and for ordinary purposes.
hautespen sexuala hautespen arrunta baino zorroztasun txikiagokoa delako; eta aldaketak hautespen natural eta sexualez atal beretan metatu direlako, eta horretara xede sexual sekundarioetara eta arruntetara egokitu direlako.