Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:Others (Zigler and Lessios 2003; McCartney and Lessios 2004; Lessios 2007) have suggested that the pattern is more likely the product of what Templeton (1981) and Noor (1999) have called ‘‘differential fusion,’’ that is, the higher probability that species with differentiated reproductive…
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