A certain species of bird has two basic varieties crested and noncrested. The birds, which generally live in flocks that contain only crested or only noncrested birds, tend to select mates of the same variety as themselves. However, if a bird that is raising a flock in which all other members are crested is later moved to a mixed flock, then that bird -- whether crested or noncrested -- is likely to select a crested mate. This fact indicates that the birds' preference for crested or noncrested mates is learned rather than genetically determined. Which one of the following, if true, provides the most support for the argument? ['In general there are few behavioral differences between the crested and noncrested birds of the species.', 'Birds of other species also tend to show preferences for mates that have one or another specific physical feature.', 'Both the crested and noncrested birds of the species tend to select mates that are similar to themselves in size and age.', 'If a bird of the species is raised in a flock that contains both crested and noncrested birds, that bird shows no preference for one variety or the other in its selection of a mate.']