单选题 .  ① Although social learning (the acquisition of specific behaviors by observing other individuals exhibiting those behaviors) is well documented among fish, few studies have investigated social learning within a developmental context in these taxa. ②Rather than investigating the development of a particular skill, Chapman, Ward, and Krause investigated the role of group density during development in later foraging success in laboratory-housed guppies. ③When raised with a small number of conspecifics (members of the same species), guppies were quicker to locate food by following a trained adult guppy than were guppies raised in large groups. ④This counterintuitive finding is explained by the fact that guppies reared in the high density condition were less likely to shoal (swim in a group) with others and, therefore, were less likely to learn the benefits of social learning. ⑤Instead, fish reared in high-density situations may learn that conspecifics are to be viewed as competitors, rather than as potential sources of adaptive information. ⑥This finding suggests that at least for guppies, the early social environment may have an effect on the capacity for social learning, if not on the socially learned behaviors themselves.32.  The primary purpose of the passage is to ______