Male bowerbirds construct elaborately decorated nests, or bowers. Basing their judgment on the fact that different local populations of bowerbirds of the same species build bowers that exhibit different building and decorative styles, researchers have concluded that the bowerbirds' building styles are a culturally acquired, rather than a genetically transmitted, trait. Which of the following, if true, would most strengthen the conclusion drawn by the researchers? ['The bowers of one species of bowerbird lack the towers and ornamentation characteristic of the bowers of most other species of bowerbird.', 'There are more common characteristics than there are differences among the bower-building styles of the local bowerbird population that has been studied most extensively.', 'Young male bowerbirds are inept at bowerbuilding and apparently spend years watching their elders before becoming accomplished in the local bower style.', 'Bowerbirds are found only in New Guinea and Australia, where local populations of the birds apparently seldom have contact with one another.']